An improved experimental method for the determination of the critical stress intensity factor KIc of brittle materials

The critical stress intensity factor K Ic is determined by a simple and accurate method, using small test specimens and a simple procedure in this paper. Single edge V-notched tension specimens made of PMMA are subjected to a load which is slowly increased until the crack begins to move from the notch tip. During the crack propagation event shadow patterns at the tip of the crack are recorded in a video recorder. Under these loading conditions, the creating real crack propagate slowly until the crack propagation velocity take an abrupt increase and the entire fracture of the specimen takes place. The stress intensity factor which correspond to the transition from the slow to fast crack speed, is the critical stress intensity factor K Ic and it can be the fracture toughness of the material. The results are accurate and in good agreement with those values of K Ic which are calculated by approximate theoretical expressions. The purpose of this paper is to introduce an improved, simple and accurate experimental method for the determination of fracture toughness of brittle materials.