Determination of mode III fracture toughness for different materials using a new designed test configuration

In practical applications it is important to determine resistance of cracked materials against out of plane sliding deformation (i.e. mode III fracture toughness (K-IIIC) using suitable testing methods. However, lack of a suitable test configuration for obtaining K-IIIC is still one of the shortcomings in fracture mechanics. In this paper, a simple specimen called Edge Notched Disc Bend (ENDB) is proposed for experimental determination of K-IIIC. This specimen is a circular disc containing an edge crack created along the disc diameter which is subjected to three-point bend loading. Both pure modes I and III loading conditions can be easily achieved by the ENDB specimen by choosing the crack orientation in appropriate direction relative to the applied loading. In order to examine the practical ability of the suggested specimen a number of ENDB specimens made of different materials including PMMA, asphalt concrete, graphite and a marble rock are tested under both modes I and III. It is also observed that for each material the mode III fracture toughness is less than the corresponding mode I fracture toughness value. The obtained fracture toughness ratio K-IIIC/K-IC for the tested materials is also predicted theoretically using a strain energy based criterion. (C) 2015 Elsevier Ltd. All rights reserved.