Tomographic investigation of the fracture toughness of the quasi-brittle specimens subjected to four-point bending test

Abstract

It is well known that detailed investigation of fracture mechanics of the quasi-brittle materials is rather complicated task as standard loading devices do not allow to interrupt loading test after reaching maximal loading force. The reason is that the point of maximal loading force is followed by the evolution of the fracture processes, due to elastic energy stored in the loading device itself. This fundamental obstacle was overcome in this work thanks to a newly developed compact four-point bending device. We show that shape of the crack can be evaluated on the basis of the so called differential tomography, which compares reference and actual states of the loaded specimen. Similarly, it is possible to evaluate displacement and strain fields by analyzing the series of loading states using the digital image correlation tools. Using such a methodology, local fracture toughness KIc is calculated thanks to information about of the crack path and evaluated CTOD parameter.