Slow crack growth and acoustic emission characteristics in COD test

Brittle material fractures at a critical value of stress intensity factor or crack opening displacement (COD) without any prior crack growth. In the ductile materials, however unstable fracture initiation may be preceded by a period of slow crack growth from the notch tip. Such slow crack growth may be an essential prelude to unstable fast fracture and thus COD at the start of slow crack growth can also be regarded as a critical value of the fracture characteristics. We have tried to apply the acoustic emission techniques to the COD test. Acoustic emission techniques can be used to detect the onset of slow crack growth and to obtain a relation between COD and AE characteristics in the COD test.