Locally Resolved Fracture Mechanisms By Using In-Situ Microscopic Testing

One of the most common reasons for materials failure is the nucleation and propagation of cracks, which makes the detailed understanding of these apparent failure processes a highly important topic from an engineering point of view. The field of fracture mechanics is growing since the 1950s through various theoretical and experimental works, but only the recent implementation of micromechanical testing devices in scanning electron microscopes (SEM), enables the possibility to observe in-situ crack propagation, with sub-micron resolution. The present work focuses on an experimental approach to evaluate crack propagation during micromechanical fracture experiments conducted in-situ in an SEM. Therefore, we utilize a continuous measurement of sample stiffness and crack length from both, experimentally measured force-displacement data as well as SEM images. The main advantage of such a combined method is the possibility of performing detailed analysis of non-linear elastic processes, frequently observed in relevant engineering materials. The current work aims to show challenges and solutions regarding the setup and implementation of such experiments, spanning from brittle model materials such as silicon to highly ductile metals

CRACK-TIP SHIELDING AND ANTI-SHIELDING BY A BIMATERIAL INTERFACE

Abstract Spacial variations of the mechanical properties have a shielding or anti-shielding effect on the crack tip by inducing an additional crack driving force term, the material inhomogeneity term, C inh . This paper explores this effect by studying the influence of a sharp bimaterial interface on the effective crack driving force in a fracture mechanics specimen. Linear elastic or elastic -ideally plastic materials are assumed with a mismatch in the elastic modulus and/or yield stress at the interface. Following a numerical stress analysis, the material inhomogeneity term, C inh , is obtained by post-processing. This parametric study is especially focused on the effect of the distance between the crack tip and the interface