Abstract
Prestrain has been pointed out to be one of the most significant factors to degrade plastic deformation capacity and fracture toughness of structural members. In this paper, resting on this viewpoint, fracture toughness tests and finite element analysis were carried out on notched plates of structural steels subjected to prestrain in order to clarify their mechanical properties. The analytical and experimental results were compared with regard to the J-integral and deformation characteristics around crack tip. The conclusions drawn through these studies are summerized as follows.
(1) The non-dimensional J-integral can be expressed as a function of the overall strain, ε, regardless of the prestrain, and hence the interrelation between J and ε can be evaluated through the rigid-perfectly plastic analysis.
(2) The plastic constraint influences greatly the correlation between J and the crack tip opening displacement, CTOD, or the contraction ahead of crack tip in the thickness direction, δz.
(3) The critical values of J, CTOD and δz at the initiation of stable crack growth, Jin, δin and δzc, decrease as the prestrain increases. The critical J-value, Jin, is represented as a function of δin or δzc. Moreover, Jin correlates closely to the uniform elongation of material.
