Tham khảo tài liệu 'new tribological ways part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Tribology in Water Jet Processes 159 continuous near the nozzle exit but separate and develop into lumps as they travel with the jet. Shimizu et al. 1998 conducted erosion tests using submerged water jets at injection pressures ranging from 49 to 118 MPa and cavitation numbers ranging from to . Since the jet decelerates faster under a submerged environment material removal by jet impingement is restricted in the region near the nozzle exit as compared to jets in air. In addition to highspeed jet impingement cavitation erosion is an additional material removal mechanism in the submerged environment. Cavitating jets are used for cleaning and shot-less peening Soyama et al. 2002 in the water jetting industry. Fig. 6. Cavitating jet at pi 69 MPa and Ơ flow direction is from left to right Abrasive jets The material removal capability of abrasive water jets in which abrasive particles are added to the water stream is much larger than the material removal capability of the pure water jets. In an abrasive water jet the stream of the water jet accelerates abrasive particles which erode the material. The material removal capability of the water is slight in abrasive water jet processes. The impact of single solid particles is the basic material removal mechanism of abrasive water jets. Meng and Ludema 1995 defined four mechanisms by which solid particles separate material from a target surface as shown in Figure 7 Momber and Kovacevic 1998 . These mechanisms are cutting fatigue brittle facture and melting which generally do not work separately but rather in combination. The importance of these mechanisms for a particular erosion process depends on several factors such as the impact angle the particle kinematic energy the particle shape the target material properties and the environmental conditions. Abrasive water jets can be classified as abrasive injection jets AIJs or abrasive suspension jets ASJs as stated earlier. Abrasive injection jets are formed
