Experimental and numerical study of moisture distribution and shrinkage crack propagation in cross section of timber members

The depth of cracks in cross section of timber can have significant impact on the bearing capacity and durability of the components. Frequently, these cracks are caused by shrinkage from moisture-induced stresses. Existence of uneven moisture distribution and the orthotropic properties of wood can cause different levels of shrinkage and/or swelling in a cross section of wood, which further induces such moisture-induced stresses in the member. This paper investigates the moisture transfer, shrinkage crack formation and propagation in cross section of timber members. Experiments for six cylindrical specimens made of Anhui fir were conducted under a drying environment to test essential parameters and study the phenomenon. The diffusion coefficient and surface emission coefficient of Anhui fir were determined based on experimental results and Fick's second law. During the experiment, different cracks in the same specimen had almost the same crack development speed, in spite of the time of crack's initiation being different. Based on the parameters determined by experiments, moisture transfer was simulated by heat transfer part of ABAQUS firstly. Then the output file from moisture transfer was input to ABAQUS as predefined field, and extended finite element method (XFEM) based linear elastic fracture mechanics (LFEM) was used for energy calculation and crack propagation. Moreover, related parameters varying with moisture content were taken into account in this simulation. Finally, good agreement of the experimental and the numerical results confirms the suitability and performance of this FEM based approach. (C) 2019 Elsevier Ltd. All rights reserved.