Experimental And Numerical Analysis Of Pure Water-jet Peening On 6061 Aluminum Alloy

Compared with the traditional shot peening, the water jet peening has the advantage of strong controllability and low cost, it can accurately control the velocity of jet, the impact angle and the impact position, which provides the possibility for strengthening the root and shoulder complex narrow areas. However,the water jet has the transient characteristics of high velocity turbulence. The existing experimental and theoretical research results can not give a qualitative and quantitative analysis on the important mechanism of the impact stress wave and the water hammer pressure.Therefore, the mechanism of water jet impact is studied based on a combination method of numerical simulation and experimental, the main research contents are as follows:(1)The structure of the pure water jet injected into the atmosphere is analyzed.Based on the theory of fluid mechanics and elastic-plastic mechanics, the formula for calculating the jet velocity and the water hammer pressure and the stagnation pressure at the exit of the nozzle is deduced.(2)Based on CEL (Coupled Lagrange - Euler) method and Johnson-Cook constitutive model, the three-dimensional finite element model of water jet impact 6061 aluminum alloy is established by using finite element software Abaqus. The water hammer pressure and stagnation pressure under different conditions are simulated, and the results are compared with the theoretical results. According to the analysis of plastic strain and impact stress wave,it is considered that that the residual pressure stress of the target is caused by the water hammer pressure, which is independent of the stagnation pressure. And parameters (velocity v, nozzle diameter d,incident angle a,impact time t and impact number of times n) influence on the residual stress field of target are simulated: The results show that increasing the jet velocity, increasing the diameter of the jet and increasing the impact times can improve the effect of the residual compressive stress.(3)Erosion mechanism of water jet is experimentally investigated, the effects of jet velocity v, nozzle movement speed vf, impact number of times n for residual stress,surface hardness and surface roughness were experimentally investigated. and appropriate parameters are selected for water jet shock strengthening to ensure that the water jet impact on the target surface without erosion or erosion is lighter.Based on the parameters determined by erosion experiment tests,the pure water jet peening tests of 6061 aluminum alloy were carried out. Residual stress, surface roughness and surface hardness of the strengthened target surface were measured by using X- ray residual stress analyzer, white light interferometer and microhardness tester. And found that the effect of residual compressive stress increases with the increase of jet velocity and impact times; With the increase of jet velocity and impact times, the roughness and surface hardness increase correspondingly; With the increase of jet velocity, the roughness decreases, but the surface hardness is unchanged.