Determination of fracture toughness using the compression fracture technique

Abstract

Many engineering materials of importance can be mechanically characterized as brittle or quasi-brittle solids. Examples include many hard polymers, ceramic composites, and low ductility metals. Fracture toughness is the measure of crack extension as a function of applied load and the resistance of the deforming material to the advance of cracking. In this investigation we use digital image correlation (DIC) for observing and studying the process of macroscopic crack initiation and propagation, and applied linear elastic fracture mechanics (LEFM) to determine the fracture toughness of these materials. We will address issues such as loading configuration for stable crack growth, diagnostics for identifying crack initiation and quantifying the extent of crack growth, and scheme for extracting the stress intensity factor at the moving crack tip. The technique described in this report has been applied to many different materials, but for the purpose of illustrating the application of the technique and data processing scheme, we choose the following materials: graphite and beryllium as materials described in this paper. This technique can be used at any rate with the only limitation being the resolution and rate at which images can be captured.