Deformation Versus Modified J Integral Resistance Curves for Ductile Materials

Abstract

The Jintegral resistance curve (or JR curve) is an important fracture property of materials and has gained broad applications in assessing the fracture behavior of structural components. Because the Jintegral concept was proposed based on the deformation theory of plasticity, the JR curve is a deformationbased result. It has been known that the JR curves of a material depend on specimen size and geometry; therefore, a modified Jintegral or Jm was proposed to minimize the size dependence. Extensive experiments have shown that the JmR curves might remain sizedependent and could not behave better than the traditional deformation JR curves. To date, however, it is noticed that the JmR curves were still used as “sizeindependentâ€‌ results in some fracture mechanics analyses. It is necessary to revisit this topic for further clarification. This paper presents a brief review on the development of deformation and modified Jintegral testing, and obtains a simple incremental Jmintegral equation. It is followed by typical experimental results with discussions on the issues of constraint or size dependence of JR and JmR curves for different steels and specimens. Finally, a recommendation is made on properly selecting a resistance curve in the fracture analysis.