A rotating arm apparatus capable of circumferential speeds up to 475 m/s (Mach 1.4) has been used to make quantitative measurements of the velocity and angle dependence of ram erosion for a wide range of materials. It has been possible to relate the mechanical properties of some materials with their rain erosion resistance. The behaviour of the drops during impact has been studied by high speed photography.

A survey is given of the rain erosion behavior of all classes of materials in the drop-impact velocity range between 200 and 400 m/sec. The results are compared with the cavitation behavior of matter and with the results of single water jet impact test. The dependence of the erosion properties upon velocity, angle of incidence, and drop size has been studied. If the materials are to be classified by increasing rain erosion strength of the most resistive representative of a material class, the order is the following: glasses, plastics, ceramics, and metals. The process which produces cracks and the material breakup is explained. The net result of this explanation provides guides for developing materials with improved erosion strength. By the energy balance of the erosion process, relations between the erosion strength and the mechanical properties of materials are given, and characteristic parameters for describing the erosion properties are proposed.