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In general the problem of erosion of materials can be divided into two categories. One is the understanding of the threshold for each material wherein the impact stresses reach a limiting value just sufficient to initiate detectable erosion either at the first blow or after repetitive blows. Evidence is presented to show that the dynamic yield strength of a material controls the threshold for the single impact whereas the endurance limit is the important property representing the threshold for multiple impacts. The second problem is the prediction of the amount of damage if the erosive forces are above the threshold for the material. The designer needs some numerical value of a property that governs the volume of erosion of a material. As of now there is no single property that can be used for this purpose just as we use various properties of materials to represent their response to static fatigue and creep loadings. A recent suggestion to use the strain energy of the material as given by the area of the stress-strain diagram from a simple tension test has a few limitations such as strain-rate effects environmental effects (for example temperature and corrosion) and the scarcity of stress-strain data under these conditions. In order to overcome these limitations a new concept known as erosion strength is introduced and it is defined as the energy absorbed per unit volume of material up to fracture under the action of the erosive forces in various environments. The methods to determine the erosion strength from an erosion test are outlined. If the concept is accepted by the engineering profession erosion strength would take its place among the other mechanical properties of materials such as yield strength ultimate strength fatigue strength creep strength hardness and corrosion fatigue.
erosion, cavitation, impingement, impact, erosion strength, strain energy, fatigue (materials)
Senior research scientist, Hydronautics, Inc., Laurel, Md.