A study of the relationship between variable level fatigue crack growth and the cyclic constitutive behaviour of steel

Sensitivity of fatigue crack growth to the material behaviour was studied in two previous numerical studies (Pommier S. Plane strain crack closure and cyclic hardening. Eng Fract Mech, in press; Pommier S, Bompard P. Bauschinger effect of alloys and plasticity-induced crack-closure: a finite element analysis. Fatigue Fract Eng Mater Struct 2000;23:129–39). It was shown, in particular, that material hardening induces a rotation of the crack tip plastic zone from the front to the back of the crack, which enhances the effects of crack closure (Pommier S. Plane strain crack closure and cyclic hardening. Eng Fract Mech, in press). The type of hardening is also of key importance: Isotropic hardening is found to lower the effective part of the fatigue cycle, while kinematic hardening (Pommier S, Bompard P. Bauschinger effect of alloys and plasticity-induced crack-closure: a finite element analysis. Fatigue Fract Eng Mater Struct 2000;23:129–39) is found to increase it. This study is devoted to check the validity of those numerical results in a 0.4% C carbon steel, which displays a high Bauschinger effect and a moderate amount of isotropic hardening. The comparison between numerical results and experiments is satisfactory.