A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Introduction

Abstract

The meeting will begin by considering the physics of liquid impact and the nature, magnitude and duration of the stresses which are produced when a solid is struck by a jet or by a drop of liquid. Even with moderate impacts the pressures developed in the solid are considerable and at high velocities the pressures are very great indeed, and are sufficient to produce deformation of the strongest solids. As we shall see a small water drop, the size of a raindrop, striking a solid moving at a speed of about 500 m/s (Mach 1.5) will exert a pressure of ca. 130 Kg/mm 2 (1.9 x 10 5 Lb./ in. 2 ) on the surface of the solid. The effect resembles that of a small explosion and at this stress level most solids and structural materials are permanently damaged either by plastic flow or by fracture. Since the pressure is applied for a very short interval of time (a few microseconds), it is the dynamic strength properties of the solid at very high rates of strain which are important. Both the nature and duration of the stresses and the mechanism by which deformation occurs will be considered. Apart from the shock pressure the rapid tangential flow of the liquid across the surface will produce deformation and these two effects interact. If the solid is subjected to multiple liquid impact, deformation will occur at much lower impact velocities and pressures. We shall consider the physics of both these processes.