Effect of 4-point bending test procedure on crack propagation in thin film stacks

Abstract

An in-depth study of 4-point bending (4PB) test method had been conducted in order to determine the influence of test parameters on measured critical energy release rate Gc and fracture location. Force loading speed proved to have an influence not only on measured Gc values, but also on quality of force–displacement curve plateau, as did the loading pin distance. While the 4PB technique is used to determine the adhesion strength of a material, a study of notch depth had also been conducted in order to determine whether it is possible to trigger the cohesive failure of the tested low-k. In addition to the experimental work, the influence of crack propagation path within the sample (symmetric and asymmetric propagation) on measured force plateau was assessed using a Finite Element Method (FEM) modeling. Assuming same interfaces triggered, crack propagation path was shown to have no influence on the value of force plateau. The FEM simulation also showed good correlation with analytical results found in literature in regards to crack opening.