Study of Crack Closure Effect of Hull Plate under Low Cycle Fatigue

The crack closure phenomenon significantly influences low cycle fatigue (LCF) crack growth. The crack closure theory deems that a crack can grow only when the applied load is greater than the fatigue crack opening and closing loads. The revised crack closure theory proposed in this paper provides a new understanding of crack growth: It is no longer the range of stress intensity factor Delta K that controls the crack growth rate, but the effective stress intensity factor Delta K-eff. Therefore, it is of great importance to study the crack closure phenomenon of LCF. A combination of experiments and the finite element method (FEM) was used to study the effect of overload on the crack closure effect, and the study was carried out using compact tensile (CT) specimens made of AH32 steel. The FEM was used to obtain the stress changes near the crack tip and the opening displacement changes in the crack trailing area after a single tensile overload, to study the intrinsic mechanism of overload on crack closure, and to obtain the LCF crack opening and closing loads by the nodal displacement method. The effect of overload on crack morphology was observed by using high-magnification electron microscopy in combination with testing.