engleski

Some Remarks About 2-D and 3-D Finite Element Modelling of Fracture Toughness Specimens with Material and Geometric Mismatch

A lot of commercial finite element (FE) package is usually tool today to analyse stress and strain fields at fracture toughness specimens. 2-D approach is then very suitable to use, regarding its simplicity and fastness. According to theory of elasticity, the user must suppose plane stress (PS) or plane strain (PE) state for chosen plane section of the specimen. However, this presumption is valid only for very thin or very thick plates, respectively. Most engineering structures have the thickness between these two extremes. In that case, the state of stress in the section's mid-plane could be imagined as mixed. Mixed state of stress combines PE state in the region near the crack tip and PS state outside of this region. The applicability of such approach could be very restricted if the structure has complex geometry. In this paper some remarks are given to influence of stress state assumptions on CTOD (d5) result for Bx2B fracture toughness specimen with material and geometric mismatch. Stress and strain fields obtained from solid FE model are presented to find out which stress state is closer to reality by 2-D FE modelling. One can conclude that plane strain state prevails in the middle of the specimen, while plane stress state is dominating on the surface. Although the specimen with X-welded overmatch joint cracked through the middle seems to have two planes of symmetry, the results for mid-plane could be accepted just as lower bound.

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