Three-dimensional stochastic modeling of metallic surface roughness resulting from pure waterjet peening

We propose a new approach named FEM-Stochastic approach for predicting the surface roughness resulting from waterjet peening of a metallic surface. This approach consists three aspects. One is Coupled Eulerian Lagrangian (CEL) simulation for studying the deformation behavior of single droplet; the second is the stochastic analysis for synthesizing a deformed surface; the third is to calculate the surface roughness parameters. CEL simulation results agree well with the liquid impact theory. Four situations with a different number of droplets (1000, 5000, 10,000 and 20,000) are analyzed, for which the deformed target surfaces and corresponding roughness profiles are shown and compared. Calculated values of roughness parameters indicate that there are three stages of evolution for the arithmetic average height R_a and quadrature average R_q. Those are: roughness increase stage, roughness decrease and roughness steady-state stage, respectively. The total roughness R_t and kurtosis parameter R_ku decline gradually when more and more droplets are modeled because the sharp ridges formed by fewer droplets are obliterated by the impingement of subsequent droplets. Skewness parameter R_sk values are all negative, no matter how many droplets, moreover, its absolute value becomes increasingly smaller as the number of droplet changes from 1000 to 20,000. The present spatial model of droplets, although still incomplete, is capable of synthesizing a deformed surface and calculating the relevant roughness parameters.