# Investigation on Residual Stress Loss during Laser
###### Abstract  
Laser peen texturing (LPT) is a novelty way of surface texturing based on laser shock processing. One of the most important benefits of LPT is that it can not only fabricate surface textures but also induce residual compressive stress for the target material. However, the residual stress loss leads to partial loss of residual compressive stress and even causes residual tensile stress at the laser spot center. This phenomenon is not conducive to improving the mechanical properties of materials. In this study, a numerical simulation model of LPT was developed and validated by comparison of surface deformation with experiments. In order to investigate the phenomenon of residual stress loss quantitatively, an evaluation method of residual stress field was proposed. The effects of laser power density and laser spot radius on the residual stress, especially the residual stress loss, were systematically investigated. It is found that with the increase of laser power density or laser spot radius, the thickness of residual compressive layer in depth direction becomes larger. However, both the magnitude and the affecting zone size of residual stress loss will be increased, which implies a more severe residual stress loss phenomenon.  
numerical simulation; residual stress loss; laser p  
However, one of the notable drawbacks of laser-shock-induced residual stress field is the relatively low residual compressive stress or even residual tensile stress at the laser spot center when laser shock pressure is greater than a threshold value. It looks as if the residual compressive stress is lost at the center of laser spot shocked zone. So, this phenomenon is called residual stress loss in this study. The residual stress loss is not conducive to improving the wear resistance, fatigue, and corrosion resistance, meanwhile, it is not conducive to making full use of laser energy [18]. So, it is necessary to study the distribution rule of residual stress and restrain the residual stress loss.  
In the past two decades, as numerical simulation can capture local variations of transient stress much easier than experiments, many researches have been reported on the numerical simulation of residual stress field during and after LSP. For example, [PERSON] et al. [19] and [PERSON] et al. [20] investigated the residual stress distribution on copper surface irradiated by micro-LSP and femtosecond LSP, respectively. [PERSON] et al. [21; 22] developed 2D and 3D FEM models to analyze the residual stress values obtained from LSP on the curved geometries. [PERSON] et al. [23] described a finite element method for simulating the residual stress distribution in multiple LSP. [PERSON] et al. [24] and [PERSON] et al. [25] predicted residual stress fields by simulation after overlapping LSP. [PERSON] et al. [26] simulated the residual stress field in two sided LSP. [PERSON] et al. [18] found that the residual stress loss may be induced by release waves caused by rapid laser impact in longitudinal directions. [PERSON] et al. [27] numerically investigated the reason for residual stress loss by analyzing the dynamic response of target material and found that square laser spot is more beneficial in restraining the residual stress loss than round laser spots.  
At present, investigations on the residual stress field after LSP are numerous, however, the studies which are focused on residual stress loss are very limited. The aim of this study is to quantitatively evaluate the residual stress loss after LSP and investigate the effect of laser power density, as well as laser spot radius, on residual stress distribution, especially on residual stress loss, which might provide a basis for restraining the residual stress loss and optimizing the process of LPT.