SHORT CRACK GROWTH MODEL IN A PARTICULATE COMPOSITE USING NONLINEAR ELASTIC FRACTURE MECHANICS

摘要

The fracture mechanics model for a long crack does not work very well with short-crack propagation when the initial crack length is less than 5.1 mm (0.2 inch). In order to investigate the short crack effect, a series of tests of particulate composite specimens with long and short cracks were performed and the results recorded on a video tape. This test data was analyzed to determine the fracture parameters. Two initial crack lengths, 2.5 mm (0.1 inches) and 7.6 mm (0.3 inches) were used in the crack propagation tests. Based on the principle of linear elastic fracture mechanics (LEFM), the stress intensity factor K_I was obtained. The instantaneous time-dependent J-integral for 0.1 and 0.3 inch crack specimens was determined by the NEFM analytical approach. The crack growth behavior was also investigated in the form of J-integral resistance curves. The calculated J-integral was reversed to derive a new K_I The new K_I was compared with the measured value obtained from LEFM analysis results to determine the feasibility of applying the linear fracture approach to the non-linear behavior of the material. The results showed that the K_I computed from the J-integral increased by 24.5%, and was at the time prior to the peak load for the 0.1 inch crack. For the 0.3 inch crack, the acceptable range was from the onset of propagation to the 9% strain stage (yield strain for the material), where the increase of the new K_I was within 15.6%.