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  • 51.
    Alawode, Abiodun
    et al.
    Stellenbosch University, South Africa.
    Eselem-Bungu, Paul
    Stellenbosch University, South Africa .
    Amiandamhen, Stephen
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Evaluation of Irvingia kernels extract as biobased wood adhesive2020In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 66, article id 12Article in journal (Refereed)
    Abstract [en]

    Irvingia tree species have been earmarked for domestication in many countries due to their potential as raw materials for various applications, which include biodiesel, cosmetics, perfume, soap, etc. Presently, there is no information on the utilization of kernel seed extract as a potential source of green wood adhesive. This study is focused on investigating the properties of adhesives produced from kernel seeds of two Irvingia wood species i.e. Irvingia gabonensis (IG) and Irvingia wombolu (IW), as well as investigating the improved properties derived from the effect of modification using a few selected modifying agents including glutaraldehyde, glyoxal, epichlorohydrin (EPI) and an acid/base type process modification. Polyethylene (PE) was used along with the glutaraldehyde, glyoxal and epichlorohydrin modifiers in the modification process. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were conducted to study the effect of modification on adhesive properties. The glycosidic carbon of the unmodified extracts and that of the EPI modified sample were not sensitive to chain conformations. Principal components (PC) 1 and 2 explained 85.19 and 9.54%, respectively, of the total variability in FTIR spectra among the modified and unmodified adhesives. The unmodified samples for IG and IW exhibited one peak with crystallization temperatures of 18.7 and 14.4 °C, respectively, indicating only one component exhibits some low degree crystallinity. The adhesive properties of the modified extracts were tested on wood veneers according to ASTM standard. The shear strength of the modified adhesives ranged from 1.5 to 3.93 MPa and 1.7 to 4.05 MPa for IG and IW, respectively. The modified samples containing PE showed marked improvement in the shear strength. The highest values were about 63% higher than the shear strength of unmodified samples with least shear strength. The results indicated that the modification of Irvingia-based adhesives had a great contribution to their performance as natural wood adhesives.

  • 52.
    Alawode, Abiodun
    et al.
    Stellenbosch University, South Africa.
    Eselem-Bungu, Paul
    Stellenbosch University, South Africa.
    Amiandamhen, Stephen
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, Department of Forest and Wood Science.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Properties and characteristics of novel formaldehyde-free wood adhesives prepared from Irvingia gabonensis and Irvingia wombolu seed kernel extracts2019In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 95, article id 102423Article in journal (Refereed)
    Abstract [en]

    There is renewed interest in the domestication of Irvingia tree species due to the potential use of various parts of the tree as raw materials for a wide range of applications such as biodiesel production, cosmetics, perfumes, soap, weight-loss supplement etc. The current study investigates the properties of extracts from the seed kernels of two Irvingia species – Irvingia gabonensis (IG) and Irvingia wombolu (IW) as natural wood adhesives. Three extraction methods using various solvent/solute media were compared in terms of yield, composition and mechanical properties. Statistically, the analysis revealed significant differences between the different extraction methods. The adhesion properties of the extracts were tested on wood veneers according to the American Society for Testing and Materials standard (ASTM D – 906-64). The shear strength of the extracts ranged from 0.55 to 1.5 MPa and 0.86 to 1.7 MPa for IG and IW, respectively. The initial decomposition temperature of all Irvingia Kernel extract ranges from 138.3 – 149.11 oC for IG and 129.5 – 145.3 oC for IW. As a result, the hot melt temperature for the adhesive experiments was set around 150 oC. The results indicate that Irvingia kernel extract is a more promising source of non-formaldehyde based adhesives in wood composite production.

  • 53.
    Alfredsen, Gry
    et al.
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Basidiomycete colonization of Scots pine sapwood quantified by qPCR and TGA2011Conference paper (Other academic)
    Abstract [en]

    Scots pine (Pinus sylvestris L.) is an important softwood species in Northern Europe and is frequently used as material for various wood protection systems. In Europe, EN 113 is the standard basidiomycete laboratory durability test method, using mass loss as evaluation criteria. In this paper quantitative real-time PCR (qPCR) and thermogravimetric analysis (TGA) was used to characterize colonization by basidiomycetes in Scots pine sapwood, but also to learn more about the EN 113 test. Two different wood sample sizes were tested. For Gloeophyllum trabeum the largest sample size gave the highest mass loss, while for the smallest samples Trametes versicolor gave the highest mass loss. As expected, fungal DNA content and mass loss in Scots pine sapwood samples decayed by G. trabeum became higher with increasing incubation time of 16 weeks. More unexpectedly, the T. versicolor DNA content in Scots pine sapwood samples was highest at the start of the incubation period and declined during the incubation period, while mass loss increased during the 28 week incubation period. The fungal colonization in the side and middle of EN 113 samples was tested. Highest DNA contents of G. trabeum were measured in the sides during 16 weeks of incubation. The T. versicolor DNA content was higher or similar in the side compared to the middle of the samples until week 20. For weeks 20 and 22 the DNA content was higher in the middle than in the sides, while for the remaining incubation period (weeks 24, 26 and 28) it was quite similar. TGA was shown to be a useful and fast method for chemical characterization of brown rot decayed wood, but cannot be used for white rot decayed wood. For T. versicolor moisture and fungal DNA explained most of the variation in mass loss, while for G. trabeum moisture explained most of the variation in mass loss. 

  • 54.
    Altgen, Michael
    et al.
    University of Göttingen, Germany.
    Adamopoulos, Stergios
    University of Göttingen, Germany.
    Militz, Holger
    University of Göttingen, Germany.
    Wood defects during industrial-scale production of thermally modified Norway spruce and Scots pine2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 1, p. 14-23Article in journal (Refereed)
    Abstract [en]

    This research investigates wood defects, particularly the formation of surface cracks, during the production of thermally modified wood and its exposure to cyclic moisture changes. Boards of Norway spruce and Scots pine originating from different steps within the production of ThermoWood® were collected and wood defects were investigated at macroscopic and microscopic scale. Subsequently, the wood was exposed to capillary wetting cycles to record its sensitivity towards cracking. After the modification process, typical anatomical defects of conventional kiln-drying became more frequent and severe, with the magnitude being to some extent depending on the presence of defects in the raw material. At microscopic scale, damages to ray parenchyma and epithelial cells as well as longitudinal cracks within the cell walls of earlywood tracheids were evident in thermally modified wood. Despite a lower water uptake and higher dimensional stability, thermally modified wood was more sensitive to surface cracking during wetting cycles than unmodified wood, i.e. at the outside face of outer boards (near bark). For limiting surface cracking of thermally modified wood during service life, the use of high-quality raw material, the exposure of the inside face of the boards (near pith) and the application of a surface coating are considered beneficial.

  • 55.
    Altgen, Michael
    et al.
    Aalto Univ, Finland.
    Willems, Wim
    FirmoLin Technol BV, Netherlands.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Rautkari, Lauri
    Aalto Univ, Finland.
    Hydroxyl accessibility and dimensional changes of Scots pine sapwood affected by alterations in the cell wall ultrastructure during heattreatment2018In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 152, p. 244-252Article in journal (Refereed)
    Abstract [en]

    There is a complex link between the water sorption behavior and the presence of accessible hydroxyl groups in the wood cell wall, which can be altered by heat-treatment (HT). This study analyses the effect of changes in the cell wall ultrastructure caused by two HT techniques on the hydroxyl accessibility, water vapor sorption and dimensional changes of Scots pine (Pinus sylvestris L.) sapwood. HT of wood in pressurized hot water at 120-170 °C was applied to cause the preferential bond cleavage, whereas HT of wood in oven-dry state in superheated steam at 180-240 °C was performed to create additional covalent cross-links within the cell wall matrix. Removal of cell wall polymers by HT and water leaching reduced the oven-dry dimensions of wood and enhanced the cellulose aggregation during drying. Cellulose aggregation restricted the cell wall shrinkage in circumferential direction, resulting in inhomogeneous shrinkage of the cell wall with only little changes in lumen volume by HT. Cellulose aggregation also reduced the water-saturated dimensions, but a decrease in swelling was only achieved when additional cross-links were formed by HT in dry state. Additional cross-links in the cell wall matrix also resulted in an additional reduction in water sorption at 25 °C and 93% RH. However, this was not caused by a further reduction in the hydroxyl accessibility. Instead, cross-linking was shown to reduce the amount of accessible OH groups that are simultaneously active in sorption, which was explained based on the concept of sorption of water dimers at hydroxyl group pairs at high RH levels.

  • 56.
    Altgen, Michel
    et al.
    Georg-August-University, Germany.
    Adamopoulos, Stergios
    Georg-August-University, Germany.
    Ala-Viikari, Jukka
    International ThermoWood Association, Finland.
    Hukka, Antti
    International ThermoWood Association, Finland.
    Tetri, Timo
    Jartek Oy, Finland.
    Militz, Holger
    Georg-August-University, Germany.
    Factors Influencing the Crack Formation in Thermally Modified Wood2012In: The Sixth European Conference on Wood Modification: Proceedings / [ed] Dennis Jones, Holger Militz, Marko Petrič, Franc Pohleven, Miha Humar, Matjaz Pavlič, University of Ljubljana , 2012, p. 149-158Conference paper (Refereed)
    Abstract [en]

    Wood anatomical changes during a thermal modification process are likely to adverselyaffect the properties of the final product. Therefore, an anatomical investigation was performed on Scots pine and Norway spruce material coming from different steps of the regular production of ThermoWood. A macroscopic evaluation using an evaluation scale between 1 and 3 revealed typical drying defects in some of the kiln dried boards. Nevertheless, at least 50 % of the unmodified boards were defect free (CR = 1), while at least 90 % of the thermally modified boards were not defect free (CR = 2 and CR = 3), thus indicating that surface cracks become more frequent and severe after the modification process. However there was no evidence of an impact of the conditioning stage on the crack formation. Even though most of the surface cracks were removed by planing, microscopic analysis by means of light and scanning electron microscopy revealed that there might still be micro-defects within the ThermoWood. Such micro-defects were mainly associated with parenchyma or epithelial cells of the rays or the resin canals. Furthermore, longitudinal cracks within the tracheids were observed within the earlywood latewood interface or within the earlywood. During repeated drying and wetting cycles, the crack formation was higher for thermally modified wood than for unmodified, despite a lower water uptake and a better dimensional stability. After the third cycle, the average crack rating of thermally modified wood was at least twice as high as for the unmodified wood. It was concluded that this increase in the crack formation might be caused by the presence of micro-defects that potentially act as a starting point for more severe cracks during swelling and shrinkage.

  • 57.
    Amiandamhen, Stephen
    University of Benin, Nigeria.
    Technology and market opportunities in fiber cement composites for small scale enterprises in Nigeria2013In: Global Journal of Agricultural Sciences, ISSN 1596-2903, Vol. 12, p. 11-14Article in journal (Refereed)
    Abstract [en]

    Solving problems of unemployment and developing new materials for buildings requires moving beyond the traditional approaches to more economical, environmentally benign performance models and design properties. New approaches should develop models based on the literature and a full understanding of the root causes of failure, derived from careful failure analysis. One of the main drivers of the development efforts in fibre based composites is the trend towards greater environmental awareness and the health hazards associated with the utilization of asbestos fibres. The key to effectively developing marketable fibre cement composites for use as building materials that can be used for construction of safe and affordable structures is to identify the research and  development and market needs for such products. This paper looks into the empirical production and market opportunities in terms of product performance accruable to locally manufactured fibre cement ceiling boards.

  • 58.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Izekor, David
    University of Benin, Nigeria.
    Assessment of the physical and mechanical properties of treated Kenaf fibre cement composites2015In: Ife Journal of Technology, ISSN 1115-9782, Vol. 23, no 2, p. 14-17Article in journal (Refereed)
    Abstract [en]

    This study investigated the effect of pretreatment on theproperties of kenaf fibre cement boards. Homogenous fibre cementboards were made from kenaf bast fibres, cement and water. Thefibres were cut into smaller sizes, mixed with cement and water andformed in rectangular moulds. After demoulding, the boards werecured for 28 days. The boards were manufactured at threepretreatment levels which include hot water, 3% CaCl2, hot water and 3% CaCl2 and a control. The fibre cement boards were tested forModulus of Rupture (MOR), Modulus of Elasticity (MOE), InternalBonding (IB), Water Absorption (WA), Thickness Swelling (TS) andLinear Expansion (LE). Also nail ability and withdrawal resistance,termite, fungi and fire resistances were also assessed. The resultsshowed that the mean MOR ranged from 1.31 to 8.25 N/mm2; the meanMOE from 78.0 to 1636.3 N/mm2 for all treated boards. Mean waterabsorption ranged from 27.52% to 67.64% and the mean thicknessswelling from 14.51% to 48.01% for all treated boards. Statisticalanalysis showed that the effects of the pretreatments were significanton the properties evaluated (p < 0.05). The study concluded that hotwater combined with CaCl2 treated boards exhibited the bestmechanical and physical properties.

  • 59.
    Amiandamhen, Stephen
    et al.
    University of Benin, Nigeria.
    Izekor, David
    University of Benin, Nigeria.
    Effect of wood particle geometry and pre-treatments on the strength and sorption properties of cement-bonded particle boards2013In: Journal of Applied and Natural Science, ISSN 0974-9411, Vol. 5, no 2, p. 318-322Article in journal (Refereed)
    Abstract [en]

    The effect of particle geometry and pretreatments on the strength and sorption properties of wood particlecement composite boards was investigated. Wood particles (flakes and sawdust) of Gmelina arborea were mixedwith cement and water in the production of composite boards. The wood particles were pretreated with hot water,calcium chloride and a combination of both treatments to enhance bonding with cement. The slurry was poured intorectangular moulds for board formation. After demoulding, the boards formed were tested for modulus of rupture(MOR), modulus of elasticity (MOE), water absorption (WA) and thickness swelling (TS). The results revealed thatthe mean MOR for flakes boards was 3.23N mm-2 while the mean MOR for sawdust boards was 3.01N mm-2. Hotwater and calcium chloride treatment produced the best effect in flake composite boards with MOR and MOE valuesof 6.90 N/mm2 and 1897.36 N mm-2 while sawdust composite boards had mean MOR and MOE values of 5.69Nmm-2 and 1664.31N mm-2 respectively. The WA rate after 24 hours of flakes and sawdust boards treated with hotwater and calcium chloride was 3.63% and 4.28% while the TS rate was 0.69% and 1.44% respectively. Particlegeometry and pretreatments significantly improved strength and sorption properties of wood particle cementcomposite boards (p<0.05).

  • 60.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa .
    Izekor, David
    University of Benin, Nigeria.
    Shrinkage characteristics of plantation grown Teak (Tectonal grandis Linn.) in Edo State, Nigeria2017In: “Forest Sector Innovations for a Greener Future”, 2017 IUFRO Division 5 Conference and 60th Society of Wood Science and Technology (SWST) International Convention, Vancouver, BC, Canada, 12th - 16th June 2017., Vancouver, BC, Canada, 2017Conference paper (Refereed)
  • 61.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Izekor, David
    University of Benin, Nigeria.
    Balogun, Adenike
    University of Benin, Nigeria.
    Performance characteristics of treated kenaf bast fibre reinforced cement composite2016In: Journal of the Indian Academy of Wood Science, ISSN 0972-172X, Vol. 13, no 2, p. 156-160Article in journal (Refereed)
    Abstract [en]

    This study investigated the effect of pretreatment on the properties of kenaf fibre cement boards. Homogenous fibre cement boards were made from kenaf bast fibres, cement and water. The fibres were cut into smaller sizes, mixed with cement and water and formed in rectangular moulds. After demoulding, the boards were cured for 28 days. The fibres were treated at three levels which included hot water, calcium chloride (CaCl2), hot water + CaCl2 and a control (untreated). The fibre cement boards were tested for Modulus of Rupture (MOR), Modulus of Elasticity (MOE), Internal Bond (IB), Water Absorption (WA), Thickness Swelling (TS) and Linear Expansion (LE). The results showed that the mean MOR ranged from 1.31 to 8.25 MPa; the mean MOE from 78.0 to 1636.3 MPa for all treated boards. Mean water absorption ranged from 27.52 to 67.64% and the mean thickness swelling from 14.51 to 48.01% for all treated boards. Statistical analysis showed that the effect of the pretreatment was significant on the properties evaluated (p < 0.05). The study concluded that boards produced from hot water combined with CaCl2 treated fibres exhibited the best mechanical and physical properties.

  • 62.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Calcium phosphate bonded wood and fiber composite panels: production and optimization of panel properties2017In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 71, no 9, p. 725-732Article in journal (Refereed)
    Abstract [en]

    The development of phosphate bonded composites with properties comparable with those of current Portland cement bonded products has been investigated. More precisely, the focus of the study was the optimization of calcium phosphate cements in combination with wood processing residues slash pine (Pinus elliottii Engelm.) planer shavings, Black wattle (Acacia mearnsii De Wild.) residues, Blue gum (Eucalyptus globulus Labill.) residues, hemp (Cannabis Sativa L.) hurds and dried crushed sugarcane bagasse (Saccharum officinarum L.) as well as pulp mill sludge and waste paper. A central composite design (CCD) for the response surface methodology (RSM) was applied for selection of the proper parameters. Mechanical tests were conducted on the composite products and the effect of the processing variables was evaluated based on the Pareto analysis of variance. The density of the wood-based panels ranged from 0.68 to 1.21 g cm−3, that of the agricultural fibers from 0.59 to 1.15 g cm−3 and that of the paper pulp panels from 0.81 to 1.21 g cm−3. The modulus of elasticity (MOE) data of the panels ranged from 1.63 to 4.92 MPa for wood, from 0.37 to 3.28 MPa for agricultural fibers and from 0.65 to 3.87 MPa for paper-pulp-based fibers. The physical properties of the composite products met the requirements for Portland-cement-bonded particleboards (EN 634-2, 2007).

  • 63.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Effect of bark on the physical and mechanical properties of phosphate bonded wood composites of black wattle (Acacia mearnsii De Wild)2016In: Forest resource and Products: Moving toward a sustainable future, 59th International Convention of the Society of Wood Science and Technology, Curitiba, Brazil, March 6 -10, 2016 / [ed] Susan LeVan-Green, Curitiba, Brazil, 2016, p. 165-173Conference paper (Refereed)
  • 64.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Arica.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Magnesium based phosphate cement binder for composite panels: A response surface methodology for optimisation of processing variables in boards produced from agricultural and wood processing industrial residues2016In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 94, p. 746-754Article in journal (Refereed)
    Abstract [en]

    This study investigates the potential use of magnesium based phosphate cement prepared from a heavy magnesium oxide and monopotassium phosphate as a binder for the production of composite panels using bio-based industrial residues such as bagasse, hemp hurds, pine sawdust, paper mill sludge and wastepaper as raw materials. These residues were used to produce light-weight and durable materials that can compare with current Portland cement based products. The phosphate binder is fast setting, cold curing and has a low carbon footprint compared to its Portland cement counterpart. The development of phosphate bonded board products promises to reduce the energy requirements in the manufacturing process of board products, and also provides an alternative route for disposal or value addition to bio-based residues by developing environmentally friendly products. The board manufacturing process was laid out on a central composite design (CCD) to model the response variable, utilizing as much residues as technically feasible. The design allowed for the production of low and medium density boards that can be used for non-structural interior finishes and partition boards. Response surface methodology (RSM) was used to show the relationships between the production variables and predict the board property by variable optimisation. Tests of mechanical and physical properties were conducted on the boards. The density of hemp boards ranged from 0.59–0.83 g/cm3, bagasse boards ranged from 0.54–0.78 g/cm3, pine boards ranged from 0.58–0.84 g/cm3, paper sludge boards ranged from 0.68–0.81 g/cm3 and wastepaper boards ranged from 0.67–0.81 g/cm3. The study has shown that it is feasible to produce phosphate based board products using bio based industrial and agricultural residues. The physical properties of the products met the minimum requirements for cement bonded particleboard (EN 634:2007) and LD-1 grade particle board (ANSI 208.1:1999).

  • 65.
    Amiandamhen, Stephen
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Stellenbosch University, Department of Forest and Wood Science .
    Meincken, Martina
    Stellenbosch University, Department of Forest and Wood Science.
    Tyhoda, Luvuyo
    Stellenbosch University, Department of Forest and Wood Science.
    Natural fibre modification and its influence on fibre-matrix interfacial properties in biocomposite materials2020In: Fibers And Polymers, ISSN 1229-9197, E-ISSN 1875-0052Article in journal (Refereed)
    Abstract [en]

    Biocomposite materials manufactured from natural fibres and polymer matrix represent a group of engineered composite products with diverse applications. These materials continue to find increasing applications due to their design flexibility, superior properties and aesthetic appeal. The applicability of these biocomposites, however, depends on theinteraction in the fibre-matrix interface. This paper reviews the state of the art research in fibre-matrix interfacial interaction based on published literature. A brief background on biocomposite materials is presented. The focus of this review is the modification of natural fibres and its effect on fibre-matrix interfacial adhesion and properties. In addition, the effect of chemical treatment on fibre composition and fibre-matrix interfacial bonding mechanism are discussed.

  • 66.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Phosphate bonded natural fibre composites2017In: Forest Sector Innovations for a Greener Future, June 12-16, 2017, Vancouver, Canada: International Union of Forest Research Organizations , 2017Conference paper (Refereed)
    Abstract [en]

    The demands for wood based composites along with increasing economic and environmental concerns on conventional wood products necessitate moving beyond the traditional processing methods to more costeffectiveand environmentally friendly approaches. In the wake of a fast-setting phosphate binder with a low carbon footprint, this study investigates the potential of different waste residues incorporated in formulated magnesium and calcium phosphate binders to produce commercially-viable composite products. The residues include forest waste from alien invasive trees, agricultural processing waste such as bagasse and hemp hurds, and wood-based industrial residues including papermill sludge, waste paper and sawmill waste. A wide range of composite products were produced that met the requirements of Portland cement particleboard (EN 634: 2007). This study presents the result of the process optimization and test conducted to product technical specifications. The development of phosphate bonded natural fibre composites utilizing lignocellulosic residues promises to bring economic potential to developing countries.

  • 67.
    Amiandamhen, Stephen
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Stellenbosch University, South Africa .
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Phosphate bonded natural fibre composites: a state of the art assessment2019In: Applied Sciences, ISSN 2523-3963, no 1, article id 910Article, review/survey (Refereed)
    Abstract [en]

    Over the last few decades, innovative wood composite products and processes have created markets for new and existing products. Inorganic bonded fibre composites have been developed for high performance applications using conventional cement and concrete. The demands for wood based composites along with increasing economic and environmental concerns on conventional wood products necessitate moving beyond the traditional processing methods to more cost-effective and environmentally friendly approaches. In the wake of the twenty-first century, a fast-setting phosphate binder with a low carbon footprint was developed, which can alternatively be utilized in wood composite development. This paper reviews the recent progress in phosphate bonded composite products, based on published literature from the last two decades. A brief background on Portland cement based natural fibre composites is presented. In addition, the mechanism of the formulation of phosphate binders, the effect of aggregates in the materials and the environmental benefits accruable to such materials are discussed.

  • 68.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    The effect of chemical treatments of natural fibres on the properties of phosphate‑bonded composite products2018In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 52, no 3, p. 653-675Article in journal (Refereed)
    Abstract [en]

    Phosphate-bonded composites are an emerging class of building materials produced from natural fibres and phosphate based cement pastes. They are durable and possess mechanical properties similar to those of Portland cement. However, the moisture absorption of natural fibre can lead to swelling which may result in the reduction in the mechanical strength properties and eventually negatively affect the long-term performance and dimensional stability of the products. This study was aimed at the modification of some properties of selected biomaterial residues in order to enhance the final properties of the phosphate-bonded composite product. Three different treatments were evaluated viz. 1% caustic alkali, 1% acetic anhydride and hot water on natural fibres derived from slash pine, black wattle and bagasse. The effect of the treatment on the fibres was evaluated via HPLC, SEM and FTIR. Further, the performance of the treated fibres was evaluated in composite panels bonded with magnesium phosphate (MgPO4) and calcium phosphate (CaPO4) cement pastes against the controls. The manufactured panels were tested for flexural properties and dimensional stability. In the MgPO4-bonded panels, the MOR increased from 0.55 MPa for untreated bagasse panels to 0.79 MPa for alkalised panels. Similarly, the MOE increased from 150.04 MPa for untreated bagasse panels to 175.65 MPa for alkalised panels. In untreated MgPO4-bonded panels, the mean density was 0.76, 078 and 0.75 g/cm3, while in alkalised panels, the mean density was 0.81, 0.81 and 0.81 g/cm3 for wattle, pine and bagasse panels, respectively. In the bagasse panels, the water absorption was 54.61% for untreated, 48.74% for hot water extracted, 42.21% for acetylated and 36.44% for alkalised MgPO4-bonded panels. This represents a percentage improvement of 11, 23 and 33%, respectively. Alkali-treated fibres had the best effect overall for all measured properties.

  • 69.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Montecuccoli, Zeno
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Barbu, Marius
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Phosphate bonded wood composite products from invasive Acacia trees occurring on the Cape Coastal plains of South Africa2018In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 76, no 2, p. 437-444Article in journal (Refereed)
    Abstract [en]

    The feasibility of manufacturing phosphatebonded wood composite board products from four locallyoccurring invasive acacia tree species (Acacia cyclops, A.saligna, A. mearnsii and A. longifolia) was studied usinga formulated magnesium oxide (MgO) and monopotassiumphosphate (KH2PO4) binder system. The optimizationfor the manufacturing process was studied using a centralcomposite statistical design, whereupon the following factorswere considered, i.e. KH2PO4:MgO ratio, the fly ashcontent as partial replacement for the binder and the woodcontent as a ratio of wood to the total inorganic content.A fitted response surface plot was used to show the effectof the main factors and their interactions on the measuredboard properties. A response surface model was developedto predict the parameters leading to the best board properties.All physical properties evaluated met or exceededthe minimum requirements for low density particleboards.The results showed that the variables considered have significanteffects on the physical properties of the boards.The optimum composite manufacturing process for makingdurable products within the scope of the studied specieswas found to be a KH2PO4/MgO ratio of 1.66, an ashcontent of 2.7% and a wood/inorganic ratio of 0.96 for theselected wood species.

  • 70.
    Andreasson, Robert
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Jansson, Pontus
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Analys av sprickdetektion vid automatisk avsyning av granvirke: med avseende på sprickors bredd, längd och djup2008Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This degree project aims to examine any connections between superficial cracks in timber, in terms of dimensions and characteristics, a matter insufficiently addressed by today's visual grading systems. The projects emphasis lies within the practical studies of cracks, characteristics and dimensions, within the acquired samples. In essence, the survey set out to determine superficial dimensions, depth, type and position of cracks by using a visual grading system (WoodEye), and by comparing the results by manually measuring a number of crosscutted cracks. The material used in the experiments and which formed the basis for subsequent analysis has been of such a nature that it could be equated with structural timber normally defined under the European Standard EN 14081-1.

    The project has encompassed the analysis of 568 examples of cracks consisting of 8 various types of cracks. By obtained results it has established that the greatest and smallest width is shown in resin pockets, respective side cracks, the greatest and least average height shown in sapwood cracks, respective resin pockets, and that the greatest average depth shown in cracks occurred from felling or hurricanes. From analysis of the cracks breadth and height in relation to depth no clear connection can be established.

  • 71.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    Mechanical properties of sound and of deteriorated softwood at different length scales: Poromicromechanical modeling and experimental investigations2011Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Due to its natural origin and its inherent heterogeneities, mechanical properties of wood are highly anisotropic and show a broad variability, not only between different wood species, but also within a tree. Similar to other biological materials, the wood mi- crostructure is well organized and hierarchically structured from the annual rings visible to the naked eye down to the wood polymers cellulose, hemicellulose, and lignin at the nanometer-scale. This thesis aims at a deeper understanding of the role of different hi- erarchical levels and their corresponding physical and chemical characteristics in relation to mechanical properties of sound wood and of deteriorated wood. This is achieved by means of micromechanical modeling and experimental analyses.

    This thesis starts with the re-formulation of an existing micromechanical model for the elastic behavior and elastic limit states of wood in the framework of poromechanics. The mechanical role of cell wall water at different hierarchical levels is investigated by means of this model. In a broader sense, the developed model allows to investigate the transition of eigenstresses from the cell wall to the softwood level. Moreover, this poromicromechanical model forms the basis for subsequent consideration of a microscopic failure criterion for lignin for the derivation of softwood failure stresses. The suitability of the modeling approach is underlined by a satisfactory agreement of the model-predicted failure stresses with experimental results of biaxial strength tests on Norway spruce.

    As a result of partly considerably different microstructural characteristics, Common yew exhibits exceptional mechanical properties compared to other softwood species. The re- lationship between microstructure and stiffness properties of Common yew and Norway spruce is investigated by means of the poromicromechanical model and mechanical tests across various length scales. Moreover, this offers the opportunity of a broader model validation. The influence of differences in microfibril angle of the S2 cell wall layer and in mass density between yew and spruce is found to be more dominant than the influence of differences in the annual ring characteristics.

    The suitability of the poromicromechanical model to predict changes in mechanical prop- erties upon fungal decay is demonstrated. For this purpose, relationships between mi- crostructure and mechanical properties of deteriorated wood are experimentally explored. Changes in mechanical properties and in the microstructure, measured at pine wood samples after standard wood durability tests using one brown rot fungus (Gloeophyl- lum trabeum) and one white rot fungus (Trametes versicolor), are presented. Transverse stiffnesses are revealed to be more sensitive to degradation than longitudinal stiffness, particularly as a result of pronounced degradation of hemicelluloses. Moreover, ultrason- ically derived anisotropy ratios of elastic stiffnesses allow to identify certain degradation mechanisms of the two considered fungi. The experimental campaign is complemented by micromechanical modeling. For this purpose, the micromechanical model is extended to take into account degradation-specific microstructural characteristics. 

  • 72.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Bocquet, Jean-Francois
    University of Lorraine, France.
    Schweigler, Michael
    Vienna University of Technology, Austria.
    Lemaitre, Romain
    University of Lorraine, France.
    Numerical modeling of the load distribution in multiple fastener joints2017In: International Conference on Connections in Timber Engineering – From Research to Standards: Proceedings of the Conference of COST Action FP1402 at Graz University of Technology / [ed] Reinhard Brandner, Andreas Ringhofer & Philipp Dietsch, Graz: Verlag der Technischen Universität Graz , 2017, p. 136-152Conference paper (Refereed)
    Abstract [en]

    Numerical modeling approaches, for the determination of load distribution in laterally loaded joints, as well as for the assignment of stiffness properties of joints for the structural analysis, are summarized in this contribution. The effect of the nonlinearity and the load-to-grain orientation dependence of connection slip, of elastic deformation in the surrounding wood matrix, and of the deviation between load and displacement direction are discussed. Comparison of various models demonstrates the pronounced effect of the load-to-grain orientation dependence and the nonlinearity in connection slip on the load distribution, particularly in case of moment loading. The effect of elastic deformation in the wood matrix on the load distribution increases with increased size of joints, even more pronounced when joints are loaded by a shear force perpendicular to the grain. In case of normal force loading, the non-uniform load distribution due to elastic deformation in the wood matrix reduces rapidly with increased relative joint displacement. Pros and cons of the modeling approaches as well as necessary input data are discussed in relation to the design process and European standardization.

  • 73. Bader, Thomas K.
    et al.
    Braovac, Susan
    Fackler, Karin
    Hofstetter, Karin
    Stiffness Properties of the Archaeological Oak Wood from the Oseberg Ship2011In: Cultural Heritage Preservation.EWCHP - 2011: Proceedings of the European Workshop on Cultural Heritage Preservation. Berlin, Germany, September 26 to 28, 2011, Fraunhofer IRB Verlag, 2011, p. 164-170Conference paper (Refereed)
  • 74.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Braovac, Susan
    University of Oslo, Norway.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Microstructure-Stiffness Relations of the Ancient Oak Wood from the Oseberg Ship2010In: International Workshop on "Modeling Mechanical Behavior of Wooden Cultural Objects", Krakow, 2010, p. 22-23Conference paper (Other academic)
  • 75.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Dastoorian, Foroogh
    Vienna University of Technology, Austria ; University of Tehran, Iran.
    Ebrahimi, Ghanbar
    University of Tehran, Iran.
    Unger, Gerhard
    Vienna University of Technology, Austria.
    Lahayne, Olaf
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Pichler, Bernhard
    Vienna University of Technology, Austria.
    Combined ultrasonic-mechanical characterization of orthotropic elastic properties of an unrefined bagasse fiber-polypropylene composite2016In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 95, p. 96-104Article in journal (Refereed)
    Abstract [en]

    Use of wood-fiber plastics for construction purposes calls for comprehensive understanding of their anisotropic mechanical properties. As a respective contribution, we here report the first-ever complete elasticity characterization of an orthotropic bagasse fiber polypropylene composite, requiring identification of nine independent constants. For this purpose, we carry out characterization in principal material directions. Six diagonal stiffness tensor components are quantified based on ultrasonic longitudinal and shear wave velocity measurements; and three diagonal compliance tensor components are identified as the inverses of three Young’s moduli derived from unloading regimes of quasi-static uniaxial compression tests. Combination of all measurement data in the framework of orthotropic linear elasticity provides access to all off-diagonal stiffness and compliance tensor components, opening the door to quantifying six Poisson’s ratios. 

  • 76.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Poroelastic properties of hardwood at different length scales2013In: Poromechanics V: proceedings of the fifth Biot Conference on Poromechanics, July 10-12, 2013, Vienna, Austria / [ed] Christian Hellmich, Bernhard Pichler, Dietmar Adam, Reston: American Society of Civil Engineers (ASCE), 2013, p. 1830-1836Conference paper (Other academic)
    Abstract [en]

    Hardwoods show a very complex, hierarchically organized microstructure. Slight structural differences at various length scales bring about a huge variety of hardwood species. This motivates the development of a micromechanical model for hardwood. Since differences in the microstructure of the material can be considered in the model, it offers the opportunity to explain the variability of mechanical properties of the whole class of hardwood. The micromechanical model is formulated in the framework of poroelasticity. In this contribution, poroelastic properties at different length scales of the material are discussed. Validation of the micromechanical model is based on an extensive experimental database covering elastic properties and microstructural characteristics of different temperate and tropical hardwood species. Exemplary parameter studies demonstrate the ability of the model to study the contribution of specific microstructural characteristics to the load transfer and the deformation characteristics of wood. 

  • 77.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Micromechanical Modeling of Wood: Multiscale Modeling and Model Validation2013Conference paper (Other academic)
    Abstract [en]

    Due to its natural origin and its inherent heterogeneities, mechanical properties of wood are highlyanisotropic and show a broad variability, not only between different wood species, but also within a tree [1].Similar to other biological materials, the wood microstructure is well organized and hierarchically structuredfrom the annual rings visible to the naked eye down to the wood polymers cellulose, hemicellulose, andlignin at the nanometer-scale. The aim of the research conducted at the Institute for Mechanics of Materialsand Structures is a deeper understanding of the role of different hierarchical levels and their correspondingphysical and chemical characteristics in relation to mechanical properties of softwood and hardwood. This isachieved by means of micromechanical modeling and experimental analyses at various length scales.

    A micromechanical model provides the opportunity to predict poroelastic properties of softwood andhardwood tissues at different hierarchical levels from microstructural and compositional data [1,2]. Thehierarchical organization of wood is mathematically represented in a multiscale model. Effective poroelasticproperties are predicted by means of continuum micromechanical approaches (self-consistent method andMori-Tanaka method), the unit cell method, and laminate theory. These approaches are extended to accountfor water-induced eigenstresses within representative volume elements and repetitive unit cells, which aresubsequently upscaled to the macroscopic wood level.

    Verification of the micromechanical model for softwood and hardwood with a comprehensive experimentaldataset, shows that it suitably predicts elastic properties at different length scales under the assumption ofundrained conditions [3,4]. Moreover, Biot tensors, expressing how much of the cell wall water-induced porepressure is transferred to the boundary of an overall deformation-free representative volume element (RVE),and Biot moduli, expressing the porosity changes invoked by a pore pressure within such an RVE can bestudied at different length scales. Consequently, the relevance and the contribution of specificmicrostructural characteristics to the load transfer and the deformation characteristics in case of moisturechanges in wood can be studied. Besides the scientific interest in structure-function-relationships, theseinvestigations are motivated by the growing importance of wood as building material.

  • 78.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Fackler, Karin
    Vienna University of Technology, Austria.
    Ters, Thomas
    Vienna University of Technology, Austria.
    Braovac, Susan
    University of Oslo, Norway.
    A nano to macroscale study on structure-mechanics relationships of archaeological oak2013In: Journal of Cultural Heritage, ISSN 1296-2074, E-ISSN 1778-3674, Vol. 14, no 5, p. 377-388Article in journal (Refereed)
    Abstract [en]

    Mechanical properties of wood at different length scales of its hierarchical structure are governed by structural and compositional properties on smaller length scales. This opens up the possibility to use microstructural data for estimating mechanical properties, which are difficult to assess by conventional, destructive testing but are nevertheless of high relevance for conservation practice. Herein, we investigate such microstructure-mechanics relationships for a particular example, namely the load bearing archaeological oak of the Oseberg Viking ship, displayed at the Viking Ship Museum in Oslo, Norway. In order to identify the effects of degradation on the mechanical behavior and their relations to the microstructure, recent oak specimens of different geographical origin (Norway and Austria) are investigated as well. Wood exhibits a cellular structure. Its cell walls are composed of an amorphous polymer matrix consisting of lignin and hemicelluloses and embedded, stiff cellulose fibers. At the cell level, experimental studies comprised microscopic investigations of the cellular structure, chemical analyses of the composition of the cell walls, as well as nanoindentation tests on single cell walls. The same samples were also analyzed on the macroscopic level, where additionally mass density and annual ring data were measured together with ultrasonic stiffnesses. The chemical data clearly indicate deterioration in the archaeological oak, affecting mainly hemicelluloses and amorphous cellulose. At the cell wall scale, however, this does not necessarily lead to a weaker material behavior. The nanoindentation modulus, as a measure of the cell wall stiffness, was found to even increase. This is counterintuitive to our understanding of the effects of chemical degradation. It might be due to possible modification of lignin in the Oseberg oak, and thus have a stronger effect on the indentation modulus than the concurrent weakening of the interfaces between the load-carrying cellulose fibers and the connecting cell wall matrix when analyzing wood at the microscopic level. A similar effect is also observed for the transversal stiffness of macroscopic samples, which increases. In tension-dominated loading modes, however, the degradation of the interfaces is the dominant effect, resulting for example in a considerable reduction of the macroscopic stiffness in longitudinal direction. This underlines the utmost relevance of the loading condition on the remaining load-carrying capacity of degraded wood. On the macroscale, effects of the geographical origin (i.e. growth conditions) on ring characteristics of the oak tissues override the effects of degradation on the mechanical behavior. They have to be carefully extracted in order to come up with conclusions on the effect of degradation from macroscopic test results. The identified microstructure-mechanics relationships provide the basis for–in further research steps–building mathematical models describing the relations between microstructural characteristics and macroscopic mechanical properties and, thereon, for structural analyses of historical wooden objects.

  • 79.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Shear stiffness and its relation to the microstructure of 10 European and tropical hardwood species2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 2, p. 82-91Article in journal (Refereed)
    Abstract [en]

    In this study, shear stiffness properties of 10 different hardwood species and their relation to the corresponding species-specific microstructure are investigated. For this purpose, shear stiffness of 10 different hardwood species is experimentally measured by means of ultrasonic testing. In addition, a micromechanical model for hardwood is applied in order to illustrate the influence of certain microstructural characteristics such as mass density and volume fractions of vessels and ray cells on the shear stiffness. Comprehensive microstructural and mechanical data from previous investigations of the same hardwood material support the interpretation of the microstructure–shear stiffness relationships. Mass density was confirmed to be the dominant microstructural characteristic for shear stiffness. Also, ultrasound shear wave propagation velocity increases with density, particularly in the radial-tangential (RT) plane. In addition to density, comparably higher shear stiffness GLR can be explained by comparably higher ray content and lower vessel content. As for GLT, a ring porous structure seems to lead to higher shear stiffness as compared to a diffuse porous structure. For this shear stiffness, vessel and ray content were found to have a less impact. Also, the rolling shear stiffness GRT was found to be higher for a diffuse porous structure than for a ring porous one. Moreover, the data supports that ray cells act as reinforcements in the RT plane and lead to higher GRT

  • 80.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Füssl, JosefTechnische Universität Wien, Austria.Olsson, AndersLinnaeus University, Faculty of Technology, Department of Building Technology.
    CompWood 2019 - Computational Methods in Wood Mechanics -: From Material Properties to Timber Structures: Book of Abstracts.2019Conference proceedings (editor) (Refereed)
  • 81. Bader, Thomas K.
    et al.
    Hofstetter, Karin
    Technische Universität, Austria.
    Pilzabbau von Holz: Quantifizierung des Steifigkeitsverlusts auf Basis von mikromechanischen Überlegungen2010In: Wiener Holzschutztage 2010: 25. - 26. November 2010, Wien, Wien: Wiener Holzschutztage , 2010, Vol. 28, p. 50-55Conference paper (Other academic)
    Abstract [de]

    Pilzbefall bewirkt eine Zersetzung des Materials durch Mikroorganismen und damit unweigerlich auch eine Veränderung des mechanischen Verhaltens von Holz. Die Auswirkung der mikrostrukturellen Änderungen auf makroskopisch beobachtbare mechanische Materialkennwerte wie Steifigkeit und Festigkeit lassen sich mittels Mehrskalenmodellierung abschätzen und quantifizieren. Die Eignung solcher Mehrskalenmodelle als Prognosewerkzeuge für Dauerhaftigkeitsbetrachtungen wurde im WoodWisdom-Netzwerk „WoodExter“ im Rahmen eines umfangreichen Testprogramms untersucht. Es wurde dabei sowohl ein Braunfäule verursachender Pilz (Gloephyllum trabeum) als auch ein Weißfäule verursachender Pilz (Trametes versicolor) verwendet. Die Vorgehensweise sowie die gewonnenen Einblicke und Erkenntnisse sind in diesem Beitrag zusammengefasst. Nach einer Kurzbeschreibung der hierarchischen Struktur von Holz und deren Modifikation durch Pilze folgt ein Abriss über die verwendeten Verfahren der Mehrskalenmodellierung. Der Schwerpunkt liegt in der Präsentation der Ergebnisse sowie der experimentellen Validierung des Modells durch Vergleich von Messwerten mit zugehörigen Modellvorhersagen. Schließlich werden im Ausblick mögliche Anwendungen der Modellierung skizziert. 

  • 82.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Alfredsen, Gry
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Changes in microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor Part II: Anisotropic stiffness properties2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 199-206Article in journal (Refereed)
    Abstract [en]

    Fungal decay considerably affects the macroscopic mechanical properties of wood as a result of modifications and degradations in its microscopic structure. While effects on mechanical properties related to the stem direction are fairly well understood, effects on radial and tangential directions (transverse properties) are less well investigated. In the present study, changes of longitudinal elastic moduli and stiffness data in all anatomical directions of Scots pine (Pinus sylvestris) sapwood which was degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks have been investigated. Transverse properties were found to be much more deteriorated than the longitudinal ones. This is because of the degradation of the polymer matrix between the cellulose microfibrils, which has a strong effect on transverse stiffness. Longitudinal stiffness, on the other hand, is mainly governed by cellulose microfibrils, which are more stable agains fungal decay. G. trabeum (more active in earlywood) strongly weakens radial stiffness, whereas T. versicolor (more active in latewood) strongly reduces tangential stiffness. The data in terms of radial and tangential stiffnesses, as well as the corresponding anisotropy ratios, seem to be suitable as durability indicators of wood and even allow conclusions to be made on the degradation mechanisms of fungi.

  • 83.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Alfredsen, Gry
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Decrease of stiffness properties of degraded wood predicted by means of micromechanical modeling2011In: Proceedings of the International Research Group on Wood Protection IRG/WP 11-40570, International Research Group on Wood Protection , 2011, p. 2-15Conference paper (Other academic)
    Abstract [en]

    Wood exhibits a highly anisotropic mechanical behavior due to its heterogeneous microscopic structure and composition. Its microstructure is organized in a strictly hierarchical manner from a length scale of some nanometers, where the elementary constituents cellulose, hemicelluloses, lignin, and extractives are found, up to a length scale of some millimeters, where growth rings composed of earlywood and latewood are observed. To resolve the microscale origin of the mechanical response of the macro-homogeneous but micro-heterogeneous material wood, micromechanical modeling techniques were applied. They allow for prediction of clear wood stiffness from microstructural characteristics. Fungal decay causes changes in the wood microstructure, expressed by modification or degradation of its components. Consequently, macroscopic mechanical properties are decreasing. Thus, in the same manner as for clear wood, consideration of alterations of wood in a micromechanical model allows predicting changes in the macroscopic mechanical properties. This contribution covers results from an extensive experimental program, where changes in chemophysical properties and corresponding changes in the mechanical behavior were investigated. For this purpose, Scots pine (Pinus sylvestris L.) sapwood samples were measured in the reference condition, as well as degraded by brown rot (Gloeophyllum trabeum) or white rot (Trametes versicolor). Stiffness properties of the unaffected and the degraded material were not only measured in uniaxial tension tests in the longitudinal direction, but also in the three principal material directions by means of ultrasonic testing. The experiments revealed transversal stiffness properties to be much more sensitive to degradation than longitudinal stiffness properties. This is due to the degradation of the polymer matrix between the cellulose fibers, which has a strong effect on the transversal stiffness. On the contrary, longitudinal stiffness is mainly governed by cellulose, which is more stable with respect to degradation by fungi. Consequently, transversal stiffness properties or ratios of normal stiffness tensor components may constitute suitable durability indicators. Subsequently, simple micromechanical models, as well as a multiscale micromechanical model for wood stiffness, were applied for verification of hypotheses on degradation mechanisms and model validation.

  • 84.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Alfredsen, Gry
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor Part I: Changes in chemical composition, density and equilibrium moisture content2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 191-198Article in journal (Refereed)
    Abstract [en]

    Fungal degradation alters the microstructure of wood and its physical and chemical properties are also changed. While these changes are well investigated as a function of mass loss, mass density loss and changes in equilibrium moisture content are not well elucidated. The physical and chemical alterations are crucial when linking microstructural characteristics with macroscopic mechanical properties. In the present article, a consistent set of physical, chemical and mechanical characteristics is presented, which were measured on the same sample before and after fungal degradation. In the first part of this two-part contribution, elucidating microstructure/stiffness-relationships of degraded wood, changes in physical and chemical data are presented, which were collected from specimens of Scots pine (Pinus sylvestris) sapwood degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks degradation time. A comparison of mass loss with corresponding mass density loss demonstrated that mass loss entails two effects: firstly, a decrease in sample size (more pronounced for G. trabeum), and secondly, a decrease of mass density within the sample (more pronounced for T. versicolor). These two concurrent effects are interrelated with sample size and shape. Hemicelluloses and cellulose are degraded by G. trabeum, while T. versicolor was additionally able to degrade lignin. In particular because of the breakdown of hemicelluloses and paracrystalline parts of cellulose, the equilibrium moisture content of degraded samples is lower than that in the initial state.

  • 85.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Keunecke, Daniel
    ETH Zürich, Switzerland.
    Microstructure–Stiffness Relationships of Common Yew and Norway Spruce2012In: Strain, ISSN 0039-2103, E-ISSN 1475-1305, Vol. 48, no 4, p. 306-316Article in journal (Refereed)
    Abstract [en]

    Yew (Taxus baccata L.) exhibits among conifers a unique macroscopic elastic behaviour. For example, it shows a comparatively low longitudinal elastic modulus related to its comparatively high density. We herein explore the microstructural origin of these peculiarities, aiming at the derivation of microstructure–stiffness relationships. We measure stiffness properties of yew at different hierarchical levels and compare them to corresponding stiffnesses of Norway spruce (Picea abies [L.] Karsten). Cell wall stiffness is investigated experimentally by means of nanoindentation in combination with microscopy and thermogravimetric analysis. On the macroscopic level, we perform uniaxial tension and ultrasonic tests. Having at hand, together with previously reported stiffnesses, a consistent data set of mechanical, chemical and physical properties across hierarchical levels of wood, we discuss influences of microstructural characteristics at different scales of observation. Moreover, a micromechanical model is applied to predict trends of effects of the microstructure on the investigated stiffness properties. On the cell wall level, particularly, the amount of cellulose and its orientation – which was earlier reported to be distinctly different for yew and spruce – result in differences between the two considered species. On the macroscopic scale, model predicted effects of the annual ring structure on transverse stiffness and shear stiffness are found to be smaller than effects of the microfibril angle and mass density.

  • 86.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    From lignin to spruce: Poromechanical upscaling of wood strength2011In: 2010 MRS Fall Meeting: Symposium V/NN/OO/PP – Soft Matter, Biological Materials and Biomedical Materials—Synthesis, Characterization and Applications / [ed] A.J. Nolte, K. Shiba, R. Narayan, D. Nolte, Warrendale, Pennsylvania, USA: Materials Research Society, 2011, Vol. 1301, p. 75-80Conference paper (Other academic)
    Abstract [en]

    Wood strength is highly anisotropic, due to the inherent structural hierarchy of the material. In the framework of a combined random-periodic multiscale poro-micromechanics model, we here translate compositional information throughout this hierarchy into the resulting anisotropic strength at the softwood level, based on “universal” elastic properties of cellulose, hemicelluloses, and lignin, and on the shear strength of the latter elementary constituent. Therefore, derivation of the elastic energy in a piece (representative volume element – RVE) of softwood, stemming from homogeneous macroscopic strains prescribed in terms of displacements at the boundary of the RVE and from pressure exerted by water filling the nanoporous space between the hemicelluloses-lignin network within the cell walls, with respect to the shear stiffness of lignin, yields higher order strains in the lignin phase, approximating micro-stress peaks leading to local lignin failure. Relating this (quasi-brittle) failure to overall softwood failure (or strictly speaking, elastic limit of softwood) results in a macroscopic microstructure-dependent failure criterion for softwood. The latter satisfactorily predicts the biaxial strength of spruce at various loading angles with respect to the grain direction. The model also predicts the experimentally well-established fact that uniaxial tensile and compressive strengths, as well as the shear strength of wood, depend quasi-linearly on the cell water content, but highly nonlinearly on the lumen porosity. 

  • 87.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Homogenization and Localization in a Multiscale Microporomechanical Model for Wood Strength2009Conference paper (Other academic)
  • 88.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Multiscale Microporomechanics Model for Estimation of Elastic Limit States of Softwood Materials2009Conference paper (Other academic)
  • 89.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Multiscale Microporomechanics of Softwood: Applications and Experimental Model Validation2010In: IV European Conference on Computational Mechanics (ECCM 2010), Paris, France: European Community on Computional Methods in Applied Sciences (ECCOMAS), 2010Conference paper (Other academic)
  • 90.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    On the Relevance of Lignin Failure for Softwood Strength: a Poromicromechanical Approach2011In: XI International Conference on Computational Plasticity - Fundamentals and Applications, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2011Conference paper (Other academic)
  • 91.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Poromechanical scale transitions of failure stresses in wood: from the lignin to the spruce level2010In: Zeitschrift für angewandte Mathematik und Mechanik, ISSN 0044-2267, E-ISSN 1521-4001, Vol. 90, no 10-11, p. 750-767Article in journal (Refereed)
    Abstract [en]

    Wood strength is highly anisotropic, due to the inherent structural hierarchy of the material. In the framework of a combined random-periodic multiscale poro-micromechanics model, we here translate compositional information throughout this hierarchy into the resulting anisotropic strength at the softwood level, based on “universal” elastic properties of cellulose, hemicellulose, and lignin, and on the shear strength of the latter elementary constituent. Relating, through elastic energy-derived higher-order strains in a poromechanical representative volume element, the (quasi-)brittle failure of lignin to overall softwood failure, results in a macroscopic microstructure-dependent failure criterion for softwood. The latter satisfactorily predicts the biaxial strength of spruce at various loading angles with respect to the grain direction. The model also predicts the experimentally well-established fact that uniaxial tensile and compressive strengths, as well as the shear strength of softwood, depend quasi-linearly on the cell water content, but highly nonlinearly on the lumen porosity.

  • 92.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    The poroelastic role of water in cell walls of the hierarchical composite “softwood”2010In: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 217, no 1, p. 75-100Article in journal (Refereed)
    Abstract [en]

    Wood is an anisotropic, hierarchically organized material, and the question how the hierarchical organization governs the anisotropy of its mechanical properties (such as stiffness and strength) has kept researchers busy for decades. While the honeycomb structure of softwood or the chemical composition of the cell wall has been fairly well established, the mechanical role of the cell wall water is less understood. The question arises how its capability to carry compressive loads (but not tensile loads) and its pressurization state affect mechanical deformations of the hierarchical composite “wood”. By extending the framework of poro-micromechanics to more than two material phases, we here provide corresponding answers from a novel hierarchical set of matrix-inclusion problems with eigenstresses: (i) Biot tensors, expressing how much of the cell wall water-induced pore pressure is transferred to the boundary of an overall deformation-free representative volume element (RVE), and (ii) Biot moduli, expressing the porosity changes invoked by a pore pressure within such an RVE, are reported as functions of the material’s composition, in particular of its water content and its lumen space. At the level of softwood, where we transform a periodic homogenization scheme into an equivalent matrix-inclusion problem, all Biot tensor components are found to increase with decreasing lumen volume fraction. A further research finding concerns the strong anisotropy of the Biot tensor with respect to the water content: Transverse components increase with increasing water content, while the relationship “longitudinal Biot tensor component versus volume fraction of water within the wood cell wall” exhibits a maximum, representing a trade-off between pore pressure increase (increasing the longitudinal Biot tensor component, dominantly at low water content) and softening of the cell wall (reducing this component, dominantly at high water contents). Soft cell wall matrices reinforced with very stiff cellulose fibers may even result in negative longitudinal Biot tensor components. The aforementioned maximum effect is also noted for the Biot modulus.

  • 93.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Muszynski, Lech
    Oregon State University, USA.
    Integrative Method for Micromechanical Characterization of Wood in Steel-Dowel Connections2012In: COST Action FP 0802: Experimental and Computational Micro-Characterization Techniques in Wood Mechanics, Edinburgh, UK, 2012, p. 100-101Conference paper (Other academic)
  • 94.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Muszynski, Lech
    Lederer, Wolfgang
    Eberhardsteiner, Josef
    Imaging the Micromechanical Response of Wood in Steel-Dowel Connections2013Conference paper (Other academic)
  • 95.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Schweigler, Michael
    Technische Universität Wien, Austria.
    Hochreiner, Georg
    Technische Universität Wien, Austria.
    Eberhardsteiner, Josef
    Technische Universität Wien, Austria.
    Ingenieurmodelle für die Strukturmodellierung und Nachweisführung von stiftförmigen Verbindungen im Holzbau: (Engineering models for the structural design and verification of dowel-type connections in timber structures)2017In: Österreichische Ingenieur- und Architekten-Zeitschrift, ISSN 0721-9415, Vol. 162, no 1-12, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Connections of elements in timber structures play an important role, not only due to their pronounced effect on the mechanical behavior of structures, but also due to the fact they can be decisive for the economic success of timber structures. Herein, approaches for a calculation of the ductile load-displacement behavior of dowel-type connections, of multi-dowel joints and of stresses in their timber matrix, by means of numerical methods, are presented. With these methods, kinematically compatible relative deformations of joints under arbitrary plane loading conditions and their effect on the mechanical behavior of timber structures can be reasonably predicted. The combination of the presented models and their integration in the structural analysis and the verification of timber structures lead to a more realistic prediction of their behavior (internal forces, stresses and deformations), as well as to a more economic design of timber structures. 

  • 96.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Schweigler, Michael
    Vienna University of Technology, Austria.
    Hochreiner, Georg
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Load Distribution in Multi-Dowel Timber Connections under Moment Loading: Integrative Evaluation of Multiscale Experiments2016In: Proceedings of the 2016 World Conference on Timber Engineering (WCTE) / [ed] J. Eberhardsteiner, W. Winter, A. Fadai, M. Pöll, Vienna: Vienna University of Technology , 2016Conference paper (Refereed)
    Abstract [en]

    The load distribution in multi-dowel timber connections under bending moments was investigated by means of an integrative evaluation of a hierarchically organized test program, which encompassed component tests as well as single dowel and multi-dowel connection tests. It was demonstrated that the anisotropic material behaviour of LVL, and consequently of wood in general, leads to a non-uniform distribution among the dowels.

  • 97.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology. Vienna University of Technology, Austria.
    Schweigler, Michael
    Vienna University of Technology, Austria.
    Hochreiner, Georg
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Serrano, Erik
    Lund University, Sweden.
    Dorn, Michael
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Experimental Assessment of the Load Distribution in Multi-Dowel Timber Connections2016In: 17th International Conference on Experimental Mechanics, Rhodes, Greece, July 3-7, 2016, 2016Conference paper (Other academic)
    Abstract [en]

    An integrative, hierarchically organized testing procedure for the quantification of the load distribution in multi-dowel timber connections is presented herein. The use of contactless deformation measurement systems allowed the combination of test data from single dowel and multi-dowel connections, which gave access to the loads acting on each dowel over the full loading history. As a consequence of the anisotropic material behavior of wood, a nonuniform and progressively changing load distribution among the dowels was found.

  • 98.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Modeling displacement path dependence in nailed sheathing-to-framing connections2017In: CompWood 2017 - Computational Methods in Wood Mechanics - from Material Properties to Timber Structures: Programme & Books of Abstracs / [ed] Josef Füssl, Thomas K. Bader, Josef Eberhardsteiner, Vienna: TU verlag , 2017Conference paper (Refereed)
  • 99.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Path dependence in OSB sheathing-to-framing nailed connection revealed by biaxial testing2018In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 144, no 10, article id 04018197Article in journal (Refereed)
    Abstract [en]

    OSB sheathing-to-wood framing connection, as typically used in light-frame shear walls, was experimentally examined in a novel biaxial test setup with respect to possible path dependence of the load-displacement relation. The connection with an annular-ringed shank nail was loaded under displacement control following nine different displacement paths within the sheathing plane, which coincided at a number of points. In intersection points, resultant connection force, its orientation and work performed on the connection system to reach the specific point were calculated and compared. Evaluation of experiments revealed significant path dependence with respect to orientation of force resultants at path intersection points. However, magnitude of the forces and the work carried out showed relatively small dependence of the displacement path undertaken. Comparison of uniaxial connection tests with the European yield model demonstrated strong contribution of withdrawal resistance of the ringed shank nail to its lateral strength. Results of this type are a valuable basis to build better models when simulating such connections in wood structures.

  • 100.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Wikete, Christoph
    de Borst, Karin
    Elastic Properties of Hardwood at Different Length Scales Predicted by Means of a Micromechanical Model2012In: Proceedings of the 6th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012), Vienna University of Technology, Vienna, Austria, Vienna, Austria, 2012Conference paper (Other academic)
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