Numerical investigation on spall fracture in a metallic material caused by laser shock peening

Abstract

Laser shock peening (LSP) is a very effective technology for metallic surface treatment, which has been widely used to improve fatigue life and the resistance of foreign object damage. However, when LSP is applied to a thin specimen, an undesirable result, spall fracture close to the free surface of the specimen, may occur. In this work, the spall fracture in Ti-17 alloy caused by LSP by numerical simulations is investigated. To this end, a three-dimensional (3D) finite element model is constructed, which consists of both finite elements and infinite elements in the commercial software Abaqus. In the simulation framework, the shock wave induced by laser is modeled as a pressure load varying in time and space, and the spall fracture criterion is a tensile failure model for high strain-rate dynamic problems. This simulation framework is verified and validated with the surface residual stress as the key result. Then, simulations of single-shock LSP process and multiple-shock LSP process are both conducted. The results show that spall fracture occurs within a very short time after the shock wave propagates into the specimen at a location very close to the free surface. Multiple layers of spall fracture occur inside the specimen after multiple shocks. The relation between the spall fracture and the specimen thickness, the peak pressure of shock wave and the shock number is thoroughly studied.