Issue 49

Yu. G. Matvienko, Frattura ed Integrità Strutturale, 49 (2019) 36-43; DOI: 10.3221/IGF-ESIS.49.04 40 obtained by finite element method lead to the significant error in the value of Q [23]. The J and A parameters allow describing the elastic-plastic stress field near the crack tip with sufficient accuracy. Figure 2 : Comparison of the parameters A and A 2 as functions of applied load P . Figure 3 : Comparison of the parameters A and Q as functions of applied load P . Relationship between the parameters A and p p S A  A parameter / p PEEQ ref A A A  is introduced into consideration as the unified constraint parameter to characterize in- plane and out-of-plane crack-tip constraint [12-14]. The parameter PEEQ A is the area surrounded by the equivalent plastic strain contour with specified value of strain p  , the parameter ref A is PEEQ A with same strain p  measured in a standard specimen test. Finite element method based on Gurson-Tvergaard-Needleman damage model was used to calculate the equivalent plastic strain p  distribution ahead of the crack tip for specimens with different in-plane and out-of-plane constraints. The following plastic strains p  =0.1, 0.2 and 0.3 were employed for determination of plastic contours. It was found that p  =0.2 and 0.3 provides approximately linear dependencies / C ref J J versus p A [13]. This is not a surprising result since the area inside specified strain p  is proportional to 2 J . So, the J -integral is compared to the quantity that is