Static and dynamic analyses of the effects of shim material stiffness on insert crack initiation and propagation

Abstract

Microcracks can form on the surface or inside an insert during forming or cutting processes. These microcracks tend to expand rapidly under impact loading, eventually leading to tool fracture and failure. Fracture and breakage of inserts cause significant limitations to the improvement of processing efficiency and safe production. This study investigated the effects of shim stiffness (using Young's modulus) on the stress distribution in the insert and at the crack tip under static and dynamic (impact) loading conditions, thereby providing a theoretical basis for correctly designing and selecting inserts for indexable tools. The extended finite element method (XFEM) was used to develop a 3D simulation model for an insert–shim system. The model was used to study crack initiation and expansion in the insert for different rigid shims under static and dynamic loading. Analyses of the crack tip stress intensity factor, the maximum principal stress, the strain, and the angle and direction of crack deflection were performed. Additionally, interrupted cutting experiments were conducted with cemented-carbide tools for four rigid shim materials. It was concluded that under static loading conditions, a weakly rigid shim reduced the crack tip stress intensity factor and the maximum principal stress, thus reducing the probability of insert fracture and that the stiffness of the shim has no effect on the angle of crack deflection on the insert surface. The shim stiffness has a more obvious effect on the crack propagation length and internal propagation direction during dynamic loading, and a weakly rigid shim increases the deflection angle as the crack expands inside the insert, thereby reducing the downward fracture length.