Response of Fracture Nucleation Site to Weak Mechanical Pulses [chapter]

E Damaskinskaya, V Kuksenko
2007 Earthquakes and Acoustic Emission  
The study is concerned with the influence of weak mechanical pulses on development of the fracture nucleation site. The macroscopic fracture of solids is considered as not an abrupt discrete event, but as a kinetic process. We assume that the fracture development in a heterogeneous material can be described in terms of the two-stage model of fracture. At the first stage, a disperse accumulation of noninteracting cracks occurs.. When the local defect concentration in some area reaches the
more » ... reaches the threshold value, the prerequisite for the accelerated defect formation is set up. This area is referred to as the fracture nucleation site. Further defect accumulation provides conditions for the loss of stability of the fracture nucleation site, as a result, a larger defect is formed. Experimental data obtained for a wide fracture scale (from microcracks to earthquakes) supported the validity of the two-stage model. A study of acoustics emission (AE) due to the cyclical deformation of samples of granite, marble and sandstone was made. It has been found that AE pattern apparently depends on the stress magnitude. At a low stress, during the unloading after the first loading cycle AE becomes negligible and at subsequent cycles increases insignificantly. At a high stress resulting in formation of a fracture nucleation site, the unloading is not followed by a sensible drop in the AE and succeeding cycles may bring about rise of AE intensity. This is in agreement with the fact that at a certain stage of formation the fracture nucleation site develops independently of the stress magnitude.
doi:10.1201/9780203936115.ch14 fatcat:wi4plnyz7ndibkboq2dvcp6sui