Further studies on the characteristics of the T  ^* _ɛ integral: Plane stress stable crack propagation in ductile materials

Abstract

Some Characteristic behavior of the T ^* _ɛ (Atluri, Nishioka and Nakagaki (1984)) is identified in this paper through an extensive numerical study. T ^* _ɛ is a near tip contour integral and has been known to measure the magnitude of singular deformation field at crack tip for arbitrary material models.

In this paper, T ^* _ɛ is found to behave quite differently for different choices of near tip integral contours. If the integral contour moves with advancing crack tip (moving contour), then T ^* _ɛ measures primarily the energy release rate at the crack tip. It is very small for metallic materials, and tends to zero in the limit as Δa→0 for low hardening materials. Thus, T ^* _ɛ evaluated on a moving contour tends to zero as ɛ→0 and Δa→0, for low hardening materials. If the integral contour elongates as crack extends (elongating contour), then T ^* _ɛ measures total energy inside the volume enclosed by Γ_ɛ [i.e., the energy dissipated in the extending wake] plus the energy release at the crack tip. Furthermore, the difference in the behavior of CTOA and T ^* _ɛ, when the applied load is slightly perturbed, is identified. The CTOA is found to be quite insensitive to applied load change. T ^* _ɛ is found to be roughly proportional to the square of the applied load.

The functional shape of T ^* _ɛ in terms of the size ɛ of integral contour (for the elongating contour case), is identified, using the crack tip asymptotic formula of Rice (1982). Also, the behaviors of CTOA and T ^* _ɛ are discussed from the view point of Rice's asymptotic solution.

It is recommended that as a crack tip parameter for ductile materials, T ^* _ɛ with elongating path be used. CTOA is sometimes not very sensitive to the applied load change, therefore it may create some numerical problems in application phase crack propagation analysis.