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The mechanical properties of wood show a very high dependence on the moisture content (MC). A consideration of MC in numerical simulations increases the applicability of such prediction with respect to application and moisture states of the wood material. The goal of this work is to develop an accurate orthotropic elasto-plastic model for oak wood (Quercus robur L.) at two different MC levels applicable for finite element analysis (FEA). To achieve this goal, the following steps were carried out: (a) in-house standard specimens tests in compression, tension, and shear and in all three orthogonal directions, followed by three-point bending, where all specimens were conditioned to a 12 and 25.6% MC, prior to the mechanical test; (b) integration of all obtained material characteristics into the consistent numerical material models; (c) validation of the developed material models by comparing the numerically predicted values with the experimental ones; and (d) iterative calibration of the material models by adjusting the individual material characteristics to minimize error using a reference. Material models were successfully developed with the following mean relative errors: 5.2% for 12% MC and 5.8% for 25.6% MC, respectively. Both numerical material models consistently predicted the oak elasto-plastic response that can be easily integrated into any FEA.

The goal of the study was to analyze fracture properties of adhesive bond using a three-point end-notched flexure test and the compliance-based beam method. Critical strain energy release rates (G IIc ) and cohesive laws were obtained for adhesive bonds made of European beech (Fagus sylvatica L.) and adhesives such as EPI, MUF, PRF and PUR. The experiments were assisted with FE analyses employing three different material models of wood: elastic (Elas), symmetric elasto-plastic (EP) and elasto-plastic with different compressive and tensile yield stresses parallel to fiber (EP+). The highest mean G IIc was achieved for PUR (5.40 Nmm−1) and then decreased as follows: 2.33, 1.80, 1.59 Nmm−1 for MUF, EPI, and PRF, respectively. The failure of bondline was brittle and occurred at bondline for EPI, MUF and PRF, and ductile and commonly occurring in wood for PUR adhesive. The FE simulations employing cohesive models agreed well with the experimental findings for all adhesives. FE model with Elas material was found accurate enough for EPI, MUF and PRF adhesives. For PUR adhesive, the model EP+ was found to be the most accurate in prediction of maximal force. The impact of friction between lamellas may be up to 4.2% when varying friction coefficient from 0 to 1. The impact of the grain angle distortion (α) with respect to longitudinal specimen axis showed its high influence on resulting stiffness and maximal force. It was found that three-point end-notched test is suitable for EPI, MUF, and PRF, while it is less appropriate for a bond with PUR adhesive due to notable plastic behavior.

This paper presents theoretical and experimental assessment of full-scale traditional dowel-type connections in tension parallel to grain made of Norway spruce ( Picea abies L. Karst.) and English oak ( Quercus robur L.). The joint dimensions were derived from the nominal dowel diameter d = {12, 16, 20, 24} mm according to the European standards EN 383 and EN 26891. Determination of the total joints displacement and surface strain distribution on the dowels was carried out using digital image correlation (DIC) technique. The theoretical and experimental approaches were focused on the determination of the load-slip joints moduli ( K ) and the dowel load-carrying capacity ( P y ) for various dowel diameters with the same length/diameter ratio equal to 3. The theoretical solution of the load-slip joints stiffness was carried out according to the Beam on Elastic Foundation (BEF) theory and the dowel load-carrying capacity according to Johansen's yield theory based on the European yield model (EYM). The theoretical results correlated with experimental values quite well. The theoretical solution proved to be a proper way for the design of the wooden dowel-type joints from the safety perspectives.

Abrupt changes of climate have intensified during the last few decades, bringing higher risks from tree failures by either uprooting or stem breakage. To eliminate the risks, many techniques of tree assessment are being used. In the presented work, an optical technique based on 3D Digital Image Correlation (3D-DIC) was investigated as one of the tools to be used in identification of tree defects. Within the work, two ash trees were examined by pulling tests coupling 3D-DIC and standard techniques. The trees were measured in five consecutive steps of artificially made defects of two kinds - root and stem damage. We hypothesized defects can be identified using full-field strains and displacements. Results indicated that 3D-DIC provides comparable strains as standard semi-destructive extensometers. Statistical tests (α = 0.05) showed the 3D-DIC technique method is capable of identifying changes of displacements and strains after creating artificial defects in trees. However, despite the statistical differences, the practical arboricultural considerations of findings are still limited due to low absolute differences. The study also suggests there might exist path-dependency of the defect creation order when evaluating stiffness/strains from extensometers of two different positions. This could have impact on a practical assessment of tree stability in the future, but it must be further tested on larger data sets due to the proof-of-concept character of this work. In general, 3D-DIC brings extensive improvement in data acquisition quality and quantity, especially from the perspective of natural variability and heterogeneity in trees and wood. info:eu-repo/semantics/openAccess

In this paper, static bending (modulus of rupture, MOR, and modulus of elasticity, MOE) and compression strength parallel to grain (Σc??) of black alder wood (Alnus glutinosa Gaertn.) were investigated. For experimental testing, we used black alder wood from two different areas: Crni Jarci, Croatia, and Malá Byst?ice, Czech Republic. Experimental tests were carried out according to the Czech national standards: ?SN 49 0115 and ?SN 49 0116 for static bending and ?SN 49 0110 for compression strength. The samples from Malá Byst?ice showed lower values of MOR (~14%), MOE (~30%), and Σc?? (~4%), when compared to the samples from Crni Jarci. The relationship between density and strength was investigated. The difference between the studied groups at the 0.05 significance level was confirmed. The average linear correlation was found between density and the observed mechanical properties (for Σc??). The average density was 5491397645907kg m-3 for samples from Crni Jarci and 469 kg m-3 for samples from Malá Byst?ice. The results were compared with values indicated in similar studies.

[EN] The fracture properties of thermally modified beech (Fagus sylvatica) wood (TMW) at 180 degrees and 200 degrees C were evaluated in mode II using the three-point end-notched flexure (3ENF) scheme assisted by three-dimensional (3D) stereovision equipment for obtaining displacements and strains. The compliance-based beam method (CBBM) provided the strain energy release rates (G(II)) of TMW and cohesive laws for both native wood (W) and TMW. Based on the CBBM and equivalent crack length approach (ECLA), G(II) was obtained directly from the force-deflection data. The thermal modification (TM) process reduced the compressive strength by 4.4% and increased the compressive elastic modulus by 38.3%, whereas G(II) was reduced substantially by 40.8% and 67.9% at TM180 degrees C and TM200 degrees C, respectively. TM also increased wood brittleness that was visible on the displacement slip reduction. The resulting mean cohesive models can be used for numerical analyses. The fracture properties of TMW have to be taken into consideration for constructional wood application, when cyclic loading may lead to microcracking and material fatigue., The authors would like to thank COST Action FP1407 (Funder Id: https://dx.doi.org/10.13039/501100000921), the European Commission for funding the InnoRenew CoE project under the Horizon2020 Widespread-Teaming program (grant agreement #739574), the Republic of Slovenia for providing support from the European Regional Development Funds, and the financial support provided by the Internal Grant Agency (IGA) of the Faculty of Forestry and Wood Technology, Mendel University in Brno (LDF_PSV_2016015).

Tree root system belongs to a key factor of the tree stability because it provides the anchorage point to the ground/soil, beside its physiological purpose. Therefore, to assess the tree stability with a certainty, it is needed to have information about tree root-plate, ie. to know roots health state, its geometrical distribution in a space with respect to a tree and surrounding objects, to know properties of the ground (soil) and to know material properties of roots. This work assessed 10 oak trees in terms of their reaction to bending induced by a standard pulling test accompanied with optical technique based on digital image correlation to obtain displacement at various locations of tree. Trees were tested in both intact state and with soil removed from the surface of the root plate. Results showed that performed soil removal did not have statistically significant effect on apparent tree stiffness. The same conclusions were found based on data provided by both inclinometers and digital camera.