Single particle impact tests using gas gun and analysis of high strain-rate impact events in ductile materials

摘要

Removal of material by the action of impinging particles is known as erosion. Based on the understanding of the material removal mechanisms in ductile materials, in normal impact, material removal occurs predominantly by deformation whereas in oblique impacts, material is removed through a combination of cutting and deformation. Although material can be removed in cutting by a single impact, material removal through deformation requires multiple impacts. Erosion of surfaces occurs over a wide spectrum of particles sizes and velocities. In general, erosion models rely on quasi-static material properties such as; hardness, yield strength, ultimate tensile strength and strain. However, material properties change dramatically under high strain and strain-rate conditions typical of erosive environments. This can lead to serious deficiencies in the developed erosion models. Adequate understanding of the strain-rate dependent material response can help in developing predictive models for wear. Single particle impact tests were performed using a high pressure gas gun at the University of Newcastle. Using specialized attachments, particles were impacted on polished ductile samples at velocities up to 200 m s~(-1). Both angular and spherical particles have been used to demonstrate the material behaviour under high strain-rate conditions. Impact craters were analysed using scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). SEM analysis was performed to observe the surface phenomena at high strain-rate as well as micro-mechanics of the material removal process. The mechanisms observed are then discussed in light of the theories of elastic and plastic deformation, temperature variation at high strain-rates as well as the response of the flow stress at high strain-rate. Impact craters were analysed quantitatively using the LSCM. Using specialized software, crater depth and deformation volumes were calculated for individual impact craters and different impact velocity and impact angles. Based on the particle impact energy and the material removed, the unit energy for cutting and deformation are determined and compared with the values obtained in standard erosion tests. The difference between the energy factors is discussed with respect to the effects of high strain-rate and temperature increase.