Moisture-induced damage evolution in laminated beech

In a combined experimental, numerical, and analytical approach, damage onset and propagation in unidirectional and cross-laminated samples from 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. Different lamella thicknesses are studied to capture size effects. Typical situations are simulated by means of a comprehensive moisture-dependent nonlinear 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 viscoelastic, mechano-sorptive, plastic, and hygro-elastic deformations under changing moisture content in progressive damage and delamination. The stress buildup under cyclic hygric loading was shown, resulting in hygro-fatigue. It was demonstrated that a modified analytical micromechanics of damage model, originally developed for cross-ply laminates, can be employed to describe the problem of moisture-induced damage in beech lamellae.