Experimental and Analytical Program to Develop Crack Tip Fracture Criteria

摘要

The large plastic deformations at the tip of a crack in a ductile heat treatment of 4340 steel are studied numerically and experimentally. The numerical simulation of the experiment uses a small strain, incremental plasticity law, with a power law hardening behavior. Both the inplane and out-plane deformations are measured on the same speciment at the same time. The experimental technique of moire interferometry is used to measure the in-plane displacements. This technique is described in detail, including an analysis of the effort of out-of-plane rotations on the use of the technique. A three beam interferometer and a four beam interferometer are compared. The out-of-plane displacements are measured with a Twyman-Green interferometer. The analysis of this data is still underway and will be forward when completed. The numerical model is described in detail. The material properties are determined from a uniaxial test on specimens taken from the same bar as the fracture specimens and with identical heat treatment. A numerical model of the fracture specimen having 7581 degrees of freedom is used to provide data for comparison between 400 N (linear behavior) up to 75000 N (catastrophic failure of the steel specimen) in fourteen steps. (JES)