Three-Dimensional Finite Element Study of Mode Mixity for the Pull-Off Test of a Thin Film from a Stiff Substrate

摘要

Nonlinear FEA models were developed to explore the fracture modes in the pull off test to compare with the theoretical model. Since FEA simulates the actual test geometry, it will help us have a more in-depth understanding of adhesion interface failures. The constitutive relation and the energy release rate obtained by 2D FEA show good agreement with the theoretical model predictions. Furthermore, 3D FEA results show that strong edge effects are involved in the test geometry we considered. Since both the total energy release rate and the mode mixity change across the width of debond front, coupled with the unknown dependence of G_c on mixity, the in-situ shape of debond front would unlikely remain straight with increasing load. Instead, it depends both on the driving forces at the debond front and the critical fracture toughness. Both FEA and theoretical model could be helpful in characterizing adhesion or improving the durability and reliability of thin film adhesion applications. Further experimental work is needed to understand the full scenario of failure modes of thin films.