Mixed mode failure analysis of bonded joints with rate dependent interface models

The recent developments in joining technologies and the increasing use of composites materials in structural design justify the wide interest of structural mechanics researchers in bonded joints. Joints often represent the weakness zone of the structure and appropriate and rigorous mechanical models are required in order to describe deformation, durability and failure. The present work is devoted to the theoretical formulation and numerical implementation of an interface model suitable to simulate the time-dependent behaviour of bonded joints. The interface laws are formulated in the framework of viscoplasticity for generalized standard materials and describe the softening response of the joint along its decohesion process in presence of shear and tensile normal tractions. These laws are derived in a thermodynamic consistent manner and take into account the rate dependency modifications of the fracture process zone making use of a sort of non-local instantaneous dissipation. The interface constitutive laws are expressed both in rate and discrete incremental form for the purpose of numerical implementation. The consistent tangent matrix is derived. Finally, the problem of model parameters identification is approached making use of the finite element method for the experiments simulation and of an evolution strategy to solve the constrained optimization problem which mathematically represents the parameter identification inverse problem.