ELSI conference: invited lecture - Liquid impact: theory, experiment, applications

Liquid impact comes into a wide range of technological problems. The theory has developed historically from two areas: those interested in "water entr y" and the action of waves on ships and structures; and those studying liqu id drops or jets impinging on surfaces. Erosion problems caused by liquid d rops impacting surfaces occur with steam-turbines and with aircraft or miss iles travelling at high speed through rain. Cavitation damage is also close ly related to liquid impact erosion. More beneficial uses of liquid drops a nd jets are for cleaning surfaces or cutting materials. The reason a liquid /solid impact can cause so much damage is that in the initial stages of imp act the contact periphery expands supersonically (i.e., faster than stress waves in either liquid or solid). Then is, therefore, a period (the duratio n depending on the impact velocity and geometry in the contact region) when compressible loading results and pressures are not released by flow. This paper describes the background theory, the various areas of application, te chniques for producing controlled impacts in the laboratory for the velocit y range from a few meters per second to several thousands of meters per sec ond, the use of high-speed photography for studying such impacts, and the d amage processes in the solid. An area of current interest is producing IR t ransmitting ''window" materials for aircraft which have sufficient strength to resist erosion damage by rain, sand, ice and bird-strike. IR materials such as zinc sulphide and germanium are relatively weak. However, it is now possible to produce free-standing "windows" and domes made from chemically vapour-deposited diamond (CVDD). Recent advances in this area are presente d. (C) 1999 Elsevier Science S.A. All rights reserved.