This paper attempts to clarify the conditions under which the J -integral is path-independent in fracture toughness specimens with heterogeneous structure. For this purpose, three point bend specimens with thickness of 36mm consisting X-welded joint were produced with surface crack (a/W=0, 3) in the middle. The base material of the plate was high strength low allowed (HSLA) steel with about 700 MPa of yield strength. Welded joint has been performed as overmatch (mismatch factor M=1, 2). Standard fracture mechanics testing of specimens were carried out. During experiment load (F), load line displacement (LLD), crack mouth opening displacement (CMOD), crack tip opening displacement (CTOD) as well as crack extension Δ a were recorded. Plane stress and plane strain finite element (FE) models of the specimens have been performed. The validity of the numerical model has been proven comparing FE results with the same obtained experimentally. ANSYS code for the calculation of J-integral value through five paths around the crack tip has been applied. Path dependence of J-integral is more present with loading increasing, particularly after crack initiation. Calculated far field J-integral with PS assumption agrees more with experimental value. Numerical calculation of J-integral for inhomogeneous structures is possible, but one should have in mind all possible influences on results. First of all it depends on assumed state-of-stress by 2-D finite element modelling and geometry of the welded structure. |