Abstract
Abstract 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.
Highlights
Adhesive bonding of wood in any shape and size is necessary for production of modern wood products
The analytical calculation of strain energy release rate (GII) follows the equivalent crack length approach (ECLA) for determination of the resistance curve (R-curve) that is explicitly determined from the experimental forcedisplacement (P/δ) curves (Figure 3)
The work showed results for materials commonly used in wood composites and timber structures, and it demonstrated applicability of the test to determine fracture properties of wood composites that are suitable for numerical modeling
Summary
Adhesive bonding of wood in any shape and size is necessary for production of modern wood products. Mechanical tests of adhesive materials are primarily made on a macroscopic scale (e.g., following EN 302-1 2013), but microscopic investigations bring important findings about adhesive bond, especially when coupled with X-ray μCT (McKinley et al 2018). To investigate mechanical performance of adhesive bonds, lap shear test is often employed to reveal the basic properties such as shear strength of wood-adhesive complex. Adhesive bond can have similar and higher bearing capacity and stiffness to bonds using dowels connecting lamellas in laminated beams (Jelušič and Kravanja 2018). Another important property of adhesive bond is the fracture energy that needs
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