Issue 41

A. Cernescu, Frattura ed Integrità Strutturale, 41 (2017) 307-313; DOI: 10.3221/IGF-ESIS.41.41 311 The value of P op,OL is higher than the maximum force of the constant amplitude loading and this could be the reason for why the crack compliance technique could not detect the extension of the crack within plastic deformation zone. Figure 4 : The variation of crack length function of number of cycles. Figure 5 : The fatigue crack path before and after overloading Also, for plane stress state has been highlighted an apparent effect of the overloading on the character of fatigue crack propagation. In Fig. 6 there are givens the variations of fatigue crack growth rate function of the crack length for the two samples overloaded with 26% ∙ P max,CA respectively 82% ∙ P max,CA , (P max,CA is the maximum force of constant amplitude loading). Based on the recordings of loading force and respectively COD, (fig. 7), has been determined the crack opening load corresponding to the overloading cycles. The values are given in Tab. 4. a) b) Figure 6 : The variation of fatigue crack growth rate function of crack length for: a) 26%P max,CA overloading; b) 82%P max,CA overloading. Before overloading After overloading