水射流冲击固体表面的能量因素与冲蚀机理

Energy effect and erosion mechanism associated with impact on solid surface by waterjet

利用PDPA测量技术和高速数码摄像技术对压力为280 MPa的纯水湍流射流进行定量测量与流束轮廓波动分析,进而在纯水射流中加入石英砂粒,形成磨料射流,以切割Al合金试样.对磨料射流作用过的试样表面形貌进行扫描电镜观察和三维光学轮廓扫描,从而获得试样表面的小尺度形貌特征.结果表明:高速纯水射流的连续集束段是产生射流冲击能量的关键,射流断面中心区存在着明显的湍流均方根速度低谷;采用统计图像灰度值的方法能够对射流流束轮廓的波动行为进行描述,灰度值也可以作为表征射流段集束程度的依据;高速砂粒与水射流的联合作用致使试样表面产生磨削痕、截断痕和撞击痕等明显特征,这些特征与靶距有着直接的关系.

Using PDPA measurement technique and high-speed photography, the cross-sectional distribu- tions of jet velocity were determined, and the fluctuations of jet stream profile were analyzed. The turbu- lent waterjet under consideration was produced at jet pressure of 280 MPa. The quartz sand particles were added into waterjet to generate abrasive waterjet to impact A1 alloy plates. The resultant surfaces were examined by SEM and a 3D optical profiling system to obtain small-scale profiles. The results indicate that the continuous and concentrated segment of jet stream is significantly responsible for the impact capa- bility of jet stream. The segment is featured by a center valley of turbulent RMS velocity distribution. The fluctuations of jet stream profile in longitudinal direction are statistically represented by gray scale values from high-speed images. The concentration level of jet stream can be described by gray scale values. Due to the cooperative action between high speed sand particles and waterjet, cutting traces, truncation traces and impact traces are evidently presented. The traces are definitely associated with the longitudinal distance between nozzle exit and solid surface.