Direct evaluation of T*_ε integral from experimentally measured near tip displacement field, for a plate with stably propagating crack

In this paper, a method for quantitatively evaluating the T*_ε integral, directly from the measured near-tip displacement field in laboratory specimens made of metallic materials, is presented for the first time. Following Okada and Atluri (Okada, H., Atluri, S.N., 1999. Further studies on the characteristics of the T*_ε integral: plane stress stable crack propagation in ductile materials. Computational Mechanics), it is shown that T*_ε quantifies the deformation energy dissipated near the crack tip region (an elongating strip of height) per unit crack extension. To directly evaluate the T*_ε integral from the measured displacement field near an advancing crack tip, the use of the deformation theory of plasticity (J₂-D theory), and the truncation of the near crack T*_ε integral path just behind the advancing crack tip, are suggested. This suggestion is validated through some careful numerical computations. The results based on the experimental studies of Omori et al. (Omori, Y., Okada, H., Atluri, S.N., Kobayashi, A.S. T* integral analysis for SEN specimen using Moire interferometry. ATEM'95 (International Symposium on Advanced Tecnology in Experimental Mechanics JSME [Japan Society of Mechanical Engineering]), submitted for publication) show good agreement with the results of finite element analysis. The latter T*_ε values were computed with a full-finite element analysis based on a J-flow theory, using a full elongating path, as well as with the use of "cut-off" integral path, and the use of J-D plasticity.