Study on Constraint Effect at Crack Tip

Abstract

The constraint effect on fracture toughness is studied. Fracture toughness tests are conducted using CT and three-point-bend specimen. Their initial crack lengths are changed from a/W=0.1 to 0.6 in five cases, which means that the constraint at the crack tip changes. It is shown that a larger fracture toughness value is obtained by a short crack specimen than by the long crack one. Two-dimensional finite-element analyses are carried out. The crack tip stress fields are compared with HRR solutions, and it is shown that the crack-tip field deviates from the HRR solution as the crack length decreases. The Q factor is evaluated for these specimens, and the relation between J_IC and Q is obtained. The conventional J-integral is compared with that obtained by the contour integral, and the experimental results are corrected. The results show the effect of crack tip constraint on the fracture toughness value clearly. The same problems are also analyzed using Gurson's constitutive equation taking into consideration the void behaviors. The effect of the constraint on void nucleation and growth is studied.