A Depth-sensing Indentation Based Study Of The Distribution Characteristics Of The Residual Stress Field Of An Al-Li Alloy Plates Subjected To Shot-peening

Residual stress field subjected to shot-peening is generated by nonuniform plastic deformation caused by the impact of projectiles on metal surface. It can significantly affect the fatigue strength, resistance to stress corrosion and creep cracking resistance of the parts, thereby affecting the machinery and equipment performance and fatigue life. Therefore, it is important to measure accuratly and efficiently the residual stress field for guiding the effective use of shot-peening process.The progress of the primary method of testing residual stress at home and abroad are reviewed and summarized in this paper. The advantages of measurements of residual stress based on depth-sensing indentation are operating simplely and getting the mechanical properties of materials at the same time along with residual stress. Three representative models of calculating residual srteee are described. Depth-sensing indentation technique is used to study the residual stress field distribution characteristics and distributions of mechanical properties of aluminum-lithium alloy plates by two shot peening intensities (0.1mmA and0.2mmA).According to the characteristics of depth-sensitive indentation test, this study determines indentation load with the minimum indentation size effect (ISE) as shot peening residual stress field test condition. The two shot peening samples’ surface layers are polished by layer electrolytic thinning. Y.H.Lee model is used to acquire the distribution of residual stress field under two shot peening intensities. With the shot peening intensity increasing from0.1mmA to0.2mmA, surface residual compressive stress, the depth of the peak compressive residual stress and the depth of residual compressive stress field have been significantly improved. The distributions of plastic hardening layer by two shot peening intensities are described by indentation characteristic parameters. Enhancing the shot peening intensity can reduce the gradient of the plastic hardening layer and thereby obtain a more uniform strengthened layer, while a higher peening intensity will induce a deeper residual stress layer and a greater residual compressive stress field.Residual stress distributions of two shot-peening intensities were obtained along the thickness direction on the side of the specimen surface. The results show that the residual stress fields on the side of the specimen surface are basically the same as the residual stress distribution gained from the surface of the specimen. But the depth of residual stress field on the side of the specimen surface is greater than that on the surface of the specimen by same shot-peening intensity.Finite element analysis software is used to create shot peening model considersing three-dimensional multi-ball collisions. The shot peening speed, projectile contact order, projectile number of collisions are as arguments to establish contact with Almen intensity. The residual stress fileds in the simulation of different shot peening intensities are compared with the experimental values. This thesis provides a complete set of experimental work to further explore the use of depth-sensitive indentation technology testing shot peening residual stress distribution characteristics and initially set up a finite element model to simulate different shot peening intensity residual stress field.