Fracture analyses of plastically-deforming adhesive joints

A general modeling approach is developed for analyzing the fracture of plastically-deforming adhesive joints in this dissertation. This model involves using an embedded-process-zone (EPZ) model to represent the fracture of the adhesive and a nonlinear finite-element analysis (FEA) to calculate the elastic-plastic deformation of adherends. The EPZ model uses both the intrinsic joint toughness and the cohesive stresses to simulate the fracture process and allows the fracture of the adhesive to be coupled with the elastic-plastic deformation of the adherends. An important feature of the model is that the mode-mixedness is a natural outcome of the deformation history. As a result, the fracture of a plastically-deforming adhesive joint can be predicted without an a-priori knowledge of the mode-mixedness.; A systematic procedure to determine the model parameters experimentally is demonstrated. It is found that the parameters required for a numerical simulation can be obtained by comparing numerical and experimental results of two simple fracture tests: the wedge induced fracture of double-cantilever beams and the three-point bending of adhesively-bonded end-notched-flexure (ENF) specimens. More importantly, it is demonstrated that once the parameters have been found, the model can be used without any modification to simulate the fracture of other adhesive joints with different dimensions or different joint geometries under general loading conditions.; Based on this modeling approach, the fracture of a variety of plastically-deforming adhesive joints is simulated and the numerical predictions are compared with the associated experimental results. It is found that the numerical calculations are capable of providing quantitative predictions of adhesive joints under Mode-I (DCBs, symmetrical T-peel and 90°-peel joints), mode-II (ENF specimens) and mixed-mode (single lap-shear and asymmetrical T-peel joints) loading conditions. In addition, many important features related to the coupling effects between the fracture process and macroscopic plasticity are revealed in this study. In summary, this study establishes an effective analytical tool that is able to provide quantitative predictions of the fracture of plastic ally-deforming adhesive joints under general load conditions, which are of great importance to many key industries.