A numerical study of the effects of overload on fatigue crack growth in plastically compressible hardening and hardening-softening-hardening solids

Abstract

Variation of cyclic loading effect on fatigue crack growth is investigated under plane strain and small scale yielding (SSY) conditions. The material is characterized by a finite strain elastic viscoplastic constitutive model with hardening and hardening-softening-hardening hardness functions. Displacements corresponding to the isotropic linear elastic mode I crack field are prescribed on a remote boundary. The influence of cyclic stress intensity factor range ($\Delta \mathrm{K}$), load ratio (R), number of cycles (N), plastic compressibility ($\mathrm{\alpha }),$ overload and material softening on near tip deformation was studied in detail. For comparison purpose, a few results pertaining to plastically incompressible solids are also considered. The crack tip opening displacement (CTOD), plastic crack growth, deformed crack tip shape, plastic zone shape and size near the crack tip appear to depend significantly on $\Delta \mathrm{K},$ R, N, $\mathrm{\alpha },$ overload and material softening. The overload produces strong plastic deformation ahead of the crack tip and decreases the fatigue crack growth substantially.

Highlights

• Variation of cyclic loading effect on fatigue crack growth is investigated for materials characterized by a finite strain elastic viscoplastic constitutive model with hardening and hardening-softening-hardening hardness functions. Both plastically compressible and incompressible solids are considered.

• The influence of cyclic stress intensity factor range ($\Delta \mathrm{K}$), load ratio (R), number of cycles (N), plastic compressibility ($\mathrm{\alpha }),$ overload and material softening on near tip deformation was studied in detail.

• The crack tip opening displacement, plastic crack growth, plastic zone shape and size near the crack tip appear to depend significantly on $\Delta \mathrm{K},$ R, N, $\mathrm{\alpha },$ overload and material softening.

• The combination of softening or softening-hardening material response and plastic compressibility leads to major deviations in crack tip blunting and fatigue crack growth from those that prevail for a hardening material.

Keywords:

• Fatigue crack growth
• finite deformation
• overload
• compressible solids
• material softening