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Surfaces, Microstructure and Fracture Group

The two types of erosion facilities that have been developed in the laboratory over the 40 years or so that the group has been researching in this area can be separated by the erodent used, either solid or liquid erodents.

The solid particle erosion facility consists of a long tube connected to the laboratory high pressure air system. A flow valve controls the amount of air allowed into the system and can be calibrated to give a range of velocities. Sand or other solid particles are introduced via a venture section in the tube and the flow of sand can be controlled via a hopper system so that the erodent flux is well known. Different barrels are available for the system to alter the area of target being eroded, and also the velocity range (which is around 200 m/s maximum). A wide range of carefully particle sized sand fractions are available and the target chamber is fitted with an industrial vacuum cleaner so that silica dust cannot escape into the laboratory. As well as standard erosion experiments, the facility has also been used to examine phenomena such as light emission from high velocity sand impact on helicopter rotor blades.

The liquid erosion facility consists of two separate pieces of equipment, the Single Impact Jet Apparatus (SIJA) and the Multiple Impact Jet Apparatus. The SIJA uses a small gas powered gun to fire a single pellet into a reservoir of water which has a small hole on the opposite side to the impact face. The pellet compresses the water and forces it out of the hole as a jet. Owing to the air resistance this jet becomes hemispherical in flight and therefore approximates a drop when impacting the target surface. Velocities of up to 1200 m/s can be reached without much difficulty. The MIJA utilises the same principle, but incorporates a multiple shot capability and computer control. This has allowed similar machines to be produced for industrial use. The main use for both machines has been investigating materials for the aviation industry, where high speed droplet impact is of a high importance.