Comparison of 3-D Small-Scale Yielding Fatigue Crack Closure Behavior using both Nonlinear and Linear Kinematic Hardening Plasticity Constitutive Models

Kristine Cochran, University of Illinois

Fatigue is the process by which a material flaw, often a crack, experiences cyclic loading and unloading which cause the flaw to expand or grow. Quantifying the remaining life of a structural component with such a flaw depends on accurately assessing the growth rate. Experience has shown that the growth rate of a crack derives from the maximum applied load less the load required to reopen the crack. Therefore, successful modeling of fatigue crack growth relies closely on determining the opening load. In metallic materials, the extent of yielding near the cracktip strongly influences the crack opening behavior.

Most of the computational modeling in this area has employed a bilinear hardening constitutive model (BL), which oversimplifies real material behavior. The current study investigates the effects of using a more realistic plasticity model (the Frederick-Armstrong (FA) model) that features nonlinear kinematic hardening. Extensive 3-D finite element analyses were conducted using both the FA and BL constitutive models calibrated to the same material response. These studies uncovered new numerical issues associated with the FA model. The results show that the fidelity of the constitutive model has an important effect on the fatigue response of metals.

Abstract Author(s): Kristine B. Cochran