探討水射噴流衝擊法對金屬板之殘留應力分布

Abstract

本研究主要討論在水射噴流衝擊法下，鋼材受氣泡破裂所產生之衝擊壓力作用後，其壓力和應力之分布。首先利用氣泡運動方程式(Bubble dynamics equation)找出氣泡破裂位置，並分析氣泡初始條件和噴嘴的幾何對氣泡運動行為的影響，結果指出氣泡初始半徑越大、氣泡初始位置越小、噴嘴喉部半徑越大或噴嘴出口半徑越小，能使氣泡破裂位置越遠，氣泡成長到最大半徑之值變大。 本研究接著透過有限元素分析，模擬鋼材受氣泡破裂後之動態行為，並暫時將炸藥爆炸取代氣泡破裂產生之能量，並透過壓力經驗公式估算出鋼材表面所受到衝擊壓力之峰值。藉由調整炸藥爆炸能量得出和經驗公式相同之金屬表面壓力峰值。模擬結果顯示金屬鋼材受水下炸藥爆炸之衝擊作用後，表面會產生近似高斯分布的壓力，且在材料表層附近有殘留壓應力區，沿著材料深度方向會有殘留壓應力轉變成殘留拉應力的現象發生。由於此方法尚未有完整實驗數據提供參考，因此本研究之成果可作為未來相關研究參考之用。

This research aims to investigate the pressure and stress distribution of steel induced by water-jet cavitation peening processing which used the shock pressure of bubble collapsing. The bubble dynamics equation was employed to find out the bubble collapsing position and the influences of bubble initial condition and nozzle geometry on the bubble motion behavior were analyzed. The results show that the bubble collapsing position and the maximum bubble radius enhanced with bubble initial radius increasing, bubble initial position decreasing, nozzle throat radius increasing or nozzle outlet radius decreasing. Next, using finite element analysis to simulate the dynamic behavior of steel induced by bubble collapsing and replacing the energy generated by bubble collapsing with explosive blasting. The peak pressure amplitude of steel surface was obtained by tuning the explosive energy to the same pressure which is calculated by empirical equation. The simulation results show that the pressure distribution of steel surface is near a Gaussian distribution and the residual compressive stress produced on the surface layer of material. It is pointed out that there was a change from the residual compressive stress to residual tensile stress along layer depth. Due to the lack of experimental data, results of this research can be used as a reference for future research.