Chevron-notched beam technique

There are two main techniques used to measure the fracture toughness of ceramics fracture stress and hardness indentation. The former measures the load to fracture of a pre-cracked specimen using a single edge notched beam (SENB) or a chevron notched beam (CNB) sample. The main drawback of this technique is ensuring that the crack tip is atomically sharp. The second method uses the crack formed at the corners of the indentation produced during a Vickers indentation hardness test. This technique is rapid and relatively inexpensive. However, the toughness values measured are those of the surface, unlike the values obtained by fracture of the pre-cracked beams which are a measure of the bulk material properties. 

In these studies, the fracture energy was employed to evaluate the fracture toughness at high temperatures, as the critical stress intensity factor does not clearly describe it when a rising R-curve behavior is observed at high temperatures. The chevron-notched beam (CNB) technique was employed for meastning the fracture energy y [48], which is defined as follows ... 

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