Moisture-induced Damage Evolution in Laminated Beech

Structural elements made of laminated hardwood are increasingly used in timber engineering. In this combined numerical and experimental approach, damage onset and propagation in uni-directional and cross-laminated samples out of European beech due to climatic changes are studied. The inter- and intra-laminar damage evolution is characterized for various configurations adhesively bonded by three structural adhesive systems. Typical situations are simulated by means of a comprehensive moisture-dependent non-linear rheological finite element model for wood with the capability to capture delaminations. The simulations give insight into the role of different strain components such as visco-elastic, mechano-sorptive, plastic, and hygro-elastic deformations under changing moisture content in progressive damage and delamination. We show the stress buildup under cyclic hygric loading resulting in hygro-fatigue and modify an analytical micro-mechanics of damage model, originally developed for cross-ply laminates, to describe the problem of moisture-induced damage in beech lamellae.