When wood is exposed to long-term loading, creep deformation can occur because of its viscoelastic characteristic. The aim of this study was to increase the understanding and knowledge of creep deformation of a wood-based lightweight sandwich-type panel and to see if this type of panel has similar properties for creep as solid wood has. This was done by means of a study based on experiments. The panel studied consisted of two face sheets of beech wood and a core of pinewood struts cross-glued to the face sheets. A solid beech panel was used as a reference. In all, there were 27 samples for the test. The densities of the lightweight panel varied from 165 to 297 kg/m(3), compared with the density of the solid panel of 705 kg/m(3). The study consisted of two parts: a bending test and a creep test. The bending test was used to determine the maximum failure load for the panel. For the creep test, 30% of the original failure load was used. When the results from the bending tests were ranked for load capacity in relation to density, the results for the lightweight panel varied from 9.0 to 18.0 m(4)/s(2), compared with the value of the reference panel at 27.3 m(4)/s(2). This measured how effective the panel was in withstanding bending loads in relation to their density. However, this was not to say that the panel with the highest value also took the highest load in absolute terms. If the creep deformation is instead ranked in relation to density, the results for the lightweight panel varied from 10.4 to 33.7 kg/m, compared with the value of the reference panel at 45.5 kg/m. As with the bending test, these values rank how effective the panel was in resisting creep deformation in relation to density.

Introduction: Throughout many parts of the world, forests exist in one form or another. And for the timber from these forests to be used, it must be processed by, for example, sawing into planks and dried. Studies have shown that profits for the forest owners increase from beneficial processing of these raw materials. An efficient use of this raw material is to process it into lightweight panels. Some general incentives for using lightweight constructions are: economical, technical and environmental. Some general weaknesses with sandwich constructions are more sensitive to impact and bumps, risk for delamination, harder to make fastenings, and more sensitive to the concentration of point loads. This work aims to increase the knowledge of properties and design of wood based lightweight panels used for interiors and furniture. The intention with this knowledge is that it can contribute to the development of lightweight panels.

Material and method: A lightweight panel of cross glued sandwich type and a cross-glued multi-layered panel with densified face sheets have been used as an example to investigate and understand which parameters are crucial for a lightweight panel, made of wood. The lightweight panel of sandwich construction has been studied to consider the changes of shape brought about by moisture, as well as which mechanical properties this panel has, with a focus on creep deformation. Two methods for reducing the moisture-generated shape changes so as to increase the shape stability of the panel have also been studied. The methods are crossgluing and thermal treatment of the wood material. In the investigations of the panels, primarily quantitative methods in the form of empirical tests have been used. Some numerical simulations describing the moisture-generated shape changes and stresses that arise in the investigated lightweight panels were also made.

Results and discussion: Cross-gluing of a multi-layered panel and also for the lightweight panel used in this study is a way to reduce the movement in the panel, generated by moisture. The drawbacks with this method are that stresses occur in the panels when the moisture change, and this can lead to a decrease in the shape stability of the panel. Thermal treatment can also be used to decrease the moisture-generated movement in wood, and in this way increase the shape stability of the product. In those cases where the empirical experiments were combined with numerical simulations, there was good agreement between the experimental and the numerical results. With the lightweight panels a weight reduction was achieved from 307 to 540 kg/m3 compared with a solid beech wood panel. The creep deformation of the lightweight panel was better or comparable for 6 of the 8 studied groups, compared to solid beech wood panel. The study also show that is possible to adapt the mechanical properties through its design of this lightweight panel.

This study was conducted to increase the knowledge of moisture-related distortion and damage in the field of wood-based lightweight panels. By increasing the possibilities of predicting moisture-related distortion and damage, the possibilities of using lightweight wood materials could increase. The study was performed through experiments and modelling work on a wooden panel product with numerous struts and two thin outer-face sheets of beech-wood glued tightly onto the struts, as well as reference panels of solid wood. During the testing period the results showed the density of the studied lightweight panels to vary from 170 to 290 kg/m³. These panels shrunk and swelled less than the solid wood panels and reacted faster to changes of surrounding humidity and temperature. Moisture related distortions such as twist and bow were not inferior compared to the solid wood panels. Shrinkage or swelling produced moisture related stresses. This may mean that the panel will have a risk of serious damage in the form of cracks or glue release between the outer face sheet and the struts when it is exposed to intense drying. The experimental tests also followed how various damages arose in the panels. Until the damage occurred, the deformation results showed a strong agreement between the experimental and the model findings. Better knowledge of how this type of panel reacts to climate variations is important for the further design and development of this type of product.

In sawmilling, a lot of timber properties are measured online in the sorting and grading of dried timber. This may include moisture content, shape, and a host of other parameters. An important wood property that cannot be measured online is drying stresses, although it is an important parameter for many customers. Since the destructive test methods for stress determination are time consuming, no high frequency routine measurement of the internal stresses is done. In literature, there are a few examples of near infrareds (NIR) capability to detect surface stresses along the fiber direction. There is also an example of stress measurements across the grain on a Japanese wood specie during drying, however, these measurements were always done on a tangential surface. It is unknown whether NIR prediction models can predict surface tension and stress measurements across the grain of dried Norway spruce with varying characteristics, i.e. material from different logs, heart- or sapwood, different year ring orientations, etc. If the technique cannot handle the variation in material properties, such as occurs in a sawmill environment, this means that a simple NIR measurement would not be sufficient to predict the surface tension in industry. This study investigated whether surface stresses in mechanically loaded as well as dried spruce samples with varying material properties can be predicted by NIR models. The measurement data from some mechanically loaded samples showed a correlation between the predicted and actual stress values, but many other samples showed no correlation. Moreover, the data for a single sample could show a good correlation, but the prediction could be at an incorrect stress level. As for the dried samples, NIR models were good at separating the conditioned and nonconditioned samples, but had no predictive power concerning the stress level. The models used to predict the stress level in mechanically loaded samples, were also used to predict the stress in the dried samples, but there was no correlation between the measured strain and the predicted stress level. Therefore, it is concluded that there are no clear indication that NIR measurements can be used in an industrial application for predicting the surface stress level of dried Norway spruce boards.

Light-weight materials based on wood for interior fittings and furniture have been of interest for at least the last fifty years, mainly for cost-reducing reasons. Today, the increasing care of the environment and the growing interest in the concept of a sustainable society provide further impulses for the development of light-weight materials. A common consequence of the reduction in weight of such materials is deterioration in the mechanical properties, e.g. strength, stiffness and shape stability, compared to those of solid wood. New solutions for e.g. connections and mountings are also needed. Today, new panel materials are required where the disadvantages of conventional light-weight materials are less prominent and with aesthetic and tactile properties close to those of natural wood.

In this paper, a new type of light-weight panel is presented. The panel is cross-laminated in three layers and consists throughout of solid wood. The weight reduction is a consequence of the hollow middle-layer construction. The intention of the construction is to make it possible to mix species in the panel, e.g. a high-quality and high-density wood on the surface and a low-quality wood with low weight in the core, and thus to optimize the properties of the panel for a specific purpose and to keep costs down at the same time. In this first study, however, the whole panel is made of Scots pine.

Bending tests show that the glue-line between the outer layers and the core is critical for the mechanical performance of the panel and this has to be developed further.

This study shows that this light-weight panel can be used as a single component or in a system with other components for interior fittings and furniture. The current design of this light-weight panel has some deficiencies but, in addition to its low weight, it has the potential to provide the mechanical, aesthetic and tactile properties asked for.

The use of high density hardwood species for furniture and interior purposes can be limited because the weight. Keeping the weight low is important both from a user perspective and for logistic reasons in the manufacturing and distribution process. This work describes the construction and mechanical characteristics of a new type of light-weight panel in wood. The panel is a sandwich construction in three layers with hardwood as the surface layers. The surface layers are made of 6 mm thick solid beech and the core consists of solid pine wood in thicknesses of 24 or 96 mm cross-laminated to the surfaces. The total panel density was then 373 and 294 kg/m³ given a beech surface layer with a density of 725 kg/m³. The presented light-weight panel resulted in a 50-60 % decrease in the use of wood compared to a traditional edge-glued panel. Tests of the mechanical properties showed a bending stiffness in the longitudinal direction (of the core) of 2.9 kNm² for a 36 mm thick panel and 221 kNm² for a 108 mm thick panel. In the transverse direction, the corresponding values were 11 kNm² and 88 kNm². The overall results indicate that the light-weight panel presented shows promising technical and environmental properties and can thereby contribute to an increased use of hardwood species.

 Particle boards are an important material for furniture production. In this sector, two tasks have had priority during recent years: to reduce the weight of the panels and to reduce the formaldehyde emission. As the production methods have been more or less the same for decades, these tasks have to be tackled by reducing or replacing the raw material in the board production.

In this study, the possibility of replacing wood with reed canary grass (Phalaris arundinacea L.) to obtain a light-weight particle board has been studied. The boards studied were three-layered with a core of wood/reed canary grass particles and a surface of 100 % wood particles. A protein-based adhesive was tested as an alternative to a UMF adhesive to reduce the formaldehyde emission. Different combinations of densities between 250 and 450 kg/m³ were included in the study and no additional treatments were made to the raw materials.

The results showed poor mechanical and swelling properties of all the tested boards regardless of the design. The main explanation of the poor properties is the poor wetting of the reed canary grass surface by the adhesives. A pre-treatment of the reed canary grass particles with steam, lipase enzyme or alkali is suggested to increase the wettability.

Handeln av grotflis, flis från grenar och toppar vid slutavverkning, har ökatkraftigt under de senaste åren. Inmätningen sker vanligtvis vidmottagningsplatsen och betalningen sker vanligen utifrån energiinnehåll meduppgift om fukthalt.Syftet med denna studie har varit att jämföra olika mätmetoder för grotflissom bygger på volym, vikt och olika sätt att uppskatta fukthalten. Den metodsom antas som facit bygger på 10 prover per container vilket innebär 30prover per leverans. Detta ”facit” har jämförts med sex alternativa sätt attberäkna lassens energivärde. En av metoderna är den som tillämpas av VMFSyd och en annan är en metod som bygger på en finsk modell att uppskattafukthalten. Studien är avgränsad till 44 leveranser grotflis, i huvudask frånbarrträd, under vinter och sommarförhållanden och transporten har skett iekipage om tre fliscontainrar.Medelfukthalten för de vinterkörda leveranserna bestämdes via 10 prov percontainer, LNU/SLU, till 39,3 % medan VMF Syd uppmätte enmedelfukthalt på 38,7 %, via den finska metoden uppskattades fukthalten förde vinterkörda leveranserna till 45,5 %. Medelfukthalten för desommarkörda leveranserna bestämdes av LNU/SLU till 27,9 %, av VMFSyd till 27,0 % meden uppskattningen via den finska metoden gav enmedelfukthalt på 30 %.De vinterkörda ekipagen hade enligt det antagna facit, LNU/SLU, ettenergiinnehåll i medeltal på 104,2 MWh medan energiinnehållet enligtfukthalten från VMF blev energiinnehållet i medeltal 105,7 MWh och dåfukthalten bestämdes med den finska metoden blev energiinnehållet imedeltal 90,8 MWh. För de sommarkörda leveranserna blev energiinnehålleti medeltal 110,8 MWh enligt LNU/SLU, 112,5 MWh enligt VMF Syd och105,7 MWh enligt den finska metoden.När det gäller de olika mätmetoderna visade det sig att M6, energivärde direkt ifrån mätsedel, var den bästa med en kvotspridning på 6,4 % ijämförelse med antaget facitvärde beräknat enligt LNU/SLU. Anledningentill detta är att denna mätning baseras på av fukthalten och beräknat effektivtvärmevärde för varje enskild leverans medan de andra bygger på ett beräknat”erfarenhetstal” för energiinnehåll per ton respektive per m3s förleveranserna i studien. Om mätningen istället baseras på erfarenhetstalistället för fukthaltsmätning visar resultaten att volymmätning ger en mindrekvotspridning, runt 10 %, jämfört med viktbaserad mätning där kvotspridningen hamnar på ca 17 % jämfört med facit. Fukthaltsmätningenligt den finska metoden ger en kvotspridning på ca 15 %.Volymminskningen under transport för alla leveranser i studien uppmättes imedeltal till strax över 2 % och resultaten visar också att den störstavolymminskningen, ca 70 %, sker redan under de första kilometrarna.Skillnaden mellan VMFs volymmätning och den mer noggrannavolymmätningen utförda av LNU/SLU visade sig vara endast 0,5 %. Men dålassen krattats för att möjliggöra denna mätning har även VMFs inmätningförenklats.