The failure of metal-to-metal adhesive joints : numerical modelling, energy contributions and constraint effects

The present thesis focuses on the development of numerical models capable of predicting reliably, with constant material parameters, the failure of metal-to-metal adhesive joints in a large range of configurations. Two finite element-based models are considered. The first one, referred to as the AACZ model (Adherend + Adhesive + Cohesive Zone), consists of embedding in the adhesive a single row of a cohesive zone elements with zero thickness which are meant to represent and condense the damage mechanisms responsible for fracture. The second one, referred to as the MPS model (Maximum Principal Stress), considers that the conditions for steady-state crack propagation are met when the maximum principal stress reaches a particular value at a critical distance ahead of the crack tip, this particular value being needed to debond, cleave or cavitate the second-phase particles present in the adhesive. The numerical results first show that the MPS model is very promising since it reproduces accurately, over a large range of adhesive layer thicknesses and test conditions, the failure of three commercial structural adhesives exhibiting different levels of resistance to fracture or adhesive fracture energies. The numerical predictions obtained with both models are further exploited to gain a better understanding of: (i) the physical mechanisms responsible for fracture in these adhesives, (ii) the different energy terms contributing to the adhesive fracture energy, and (iii) the effects of constraint. Hence, it has been possible to determine how the adhesive fracture energy is affected as a function of the geometry of the test specimen and the type of test.(FSA 3) -- UCL, 201