An elastic-plastic kinking layer model for parallel-to-grain wood embedment behavior considering wood drilling damage

This paper presents the results of the experimental and numerical studies on the influence of drilling damage of wood on the wood embedment behavior. Wood drilling tests were conducted to quantify the distribution of wood residual strain by use of digital image correlation technique. Parallel to wood grain repetitive compression tests were also conducted to determine the mechanical properties of wood within the kinking zone. Wood half-hole bolt embedment tests were conducted, and a wood kinking layer model was proposed and incorporated into a FEM model for the wood embedment behavior simulation. The model predictions were compared with the embedment test results and results from FEM models with different consideration of the weakened wood around the bolt holes. It was found that drilling can develop significant parallel and perpendicular to grain and shear residual strain in the surrounding wood. The distribution and magnitude of the residual strains were correlated with the hole diameter and drilling speed, and the thickness of a kinking layer can be taken as 1/13 and 1/7 of the hole diameter under the low and high drilling speeds considered in this study, respectively. It was observed from the repetitive tests of wood that during the steady-state kinking process, wood exhibited nearly constant peak stress and reloading modulus of elasticity. The FEM model with the proposed kinking layer model achieved a better agreement with the test results than FEM models based on wood foundation theory or a nonlinear contact model regarding the embedment elastic modulus, the maximum load, and the distribution of the strain in the embedment zone.