Modeling fatigue crack growth in a bimaterial specimen with the configurational forces concept

A two-dimensional finite element analysis is performed to model the behavior of fatigue cracks in bimaterial specimens made of diffusion-bonded ARMCO-iron and SAE 4340 steel with an interface perpendicular to the crack plane. The numerical analyses are based on experiments conducted by Pippan et al. [Mater. Sci. Eng. A 283 (2000) 225-233]. The concept of configurational forces is used to evaluate by post-processing the crack-tip shielding and anti-shielding effects that occur due to the differences in yield stress, hardening and coefficients of thermal expansion of ARMCO-iron and SAE 4340 steel. For given values of applied stress intensity range ΔKapp and applied load ratio Rapp, the near-tip J-integral Jtip is calculated at the maximum and minimum load. To allow for crack closure, the effective near-tip stress intensity range ΔKeff,tip is evaluated from the near-tip stress intensity range ΔKtip and the near-tip load ratio Rtip. Calibration curves for homogeneous ARMCO-iron and SAE 4340 steel are used to calculate the crack growth rate da/dN from the values of ΔKeff,tip. The distance between interface and crack tip L is varied to simulate the behavior of a growing crack. The computed curves da/dN versus L curves are in good agreement with the experimental results.