VOLUME 61, ISSUE 5/2020

Especially due to the digitalization and the entry of Industry 4.0 into the wood-based panel industry, the numerical simulation of wood-based panels and the associated determination of mechanical replacement parameters is becoming more and more important. In order to obtain all nine elasticity parameters, three Poisson's ratio, three elasticity and three shear modulus are required. The determination of the Poisson's ratio is a great challenge, so that the determination is often omitted or the results show a poor repeatability. The aim of this work was to achieve a method with reliable results. This was achieved by clamping the sample in a DMTA test system, with which the sample was harmonically loaded and the length variation measured in parallel. The measurement of the transverse strain was realized by two laser Doppler vibrometers. The Poisson's ratio was calculated from the quotient of transverse and longitudinal strain. With this method, the Poisson's ratio can be determined reliably.

Vacuum press drying is a new type of process developed to compress and dry wet laminated moulded fibre bodies articles. The materials used are digested natural fibres, recycled fibres and cellulose. Shaped bodies with demanding strengths are created by vacuum-induced pressing, as well as water and steam suction. For example, potential components are recyclable moulded fibre furniture, i. e., alternatives to materials composed of several components and contain binding agents or plastics. The weight-ing of the influencing variables carried out here, using a significance test, according to Plackett and Burman, an essential step in consolidating the understanding of the process and developing potential applications. The investigation was carried out by the research group "Natural Fiber Composites and Biocomposites" of the Professorship for Wood Technology and Fiber Material Technology at Technische Universität Dresden.

A current research topic of wood based materials is the determination of the elastic material parameters. According to the current state of the art, there are hardly any complete sets of parameters to describe the mechanical behaviour of wood-based materials using an orthotropic material model. The aim of this work was to reliably determine all nine mechanical parameters. In addition to static determination methods, which were based on the existing DIN standards, the parameters were determined dynamically using the model updating method. The static methods showed a stronger directional dependence in the cover layers than in the middle layer. In addition, a large dependence on the load duration was shown, which can be explained by the time- dependent material behaviours. This non-linear property of wood-based materials also led to the fact that the dynamically identified parameters were above the statically determined characteristic values. Both methods considered separately provide reliable values with a small standard deviation. Thus, the determination of the characteristic values has to be adapted to the later load conditions.

In a research project between the Laboratory for Timber Construction at RheinMain University and Römmelt Carpentry and Hall Construction company, multi-layer OSB were examined. Curved panels, which for example could be used for curved dormers, were investigated in the research project. In addition, top layers made of oak were glued to the multi-layer OSB and were examined. For this purpose, delamination tests and pressure- shear tests were carried out with various pretreatments. Finally, joints between different multilayer OSB were examined. On the one hand, OSB panels were used for coupling, and on the other hand, glued-in perforated steel plates were used. Good results were achiev-ed especially with the approach of glued-in perforated steel plates.

Due to the high energy and water consumption in the paper industry, a new possible approach has been recently developed to transfer the production of paper products, mainly cardboard for packaging purposes, from wet processes to dry processes. It will be referred as "dry-cardboard" in the following. The following requirements are important for this approach: Firstly, dry-cardboard should have similar properties to traditional cardboard. On the other hand, it should not have a negative influence on recycling stream of the waste paper. The technology of this process is modified by MDF production in the dry process. However, innovative technologies such as dry pulping, dry gluing, air-laid process and multi-layer structure were also used.

Lap shear tests were carried out on fibre-reinforced epoxy resin with cellulose regenerated fibres (CRF). The strengths of CRF with and without sizing agents were compared. At the boundary layer between CRF and epoxy resin, insufficient bonding seems to be developed. A permanent stable structure could not be formed. The use of a sizing agent has no effect on the bondability of the fibres in the matrix. The values of the lap shear test as well as the macroscopic fracture patterns and the microscopic analyses of the fractures in the matrix do not show any significant differences between the two investigated variants.