Tensile strength of water

Abstract

THE measured tensile strength of water has long been known to be significantly less than theoretical predictions and the reduced strength is normally attributed to the presence of solid impurities that serve as nucleation sites for rupture of the liquid¹. A favourite method of measuring tensile strength is through the dynamic stressing of a liquid by an acoustic field. At sufficiently large values of the peak negative acoustic-pressure amplitude the liquid ruptures and forms a rapidly growing vapour cavity that collapses violently during the positive portion of the cycle. This cavity collapse is normally violent enough to be observed easily with the unaided eye or ear. Such an event is termed the acoustic cavitation threshold and is a measure of the tensile strength of a liquid. Although some successes have been obtained in achieving measured values of the tensile strength comparable to theoretical predictions for extremely small samples² or after extensive filtration³, I know of no current theory for the prediction of values of the dynamic tensile strength for ordinary distilled water. Using a modified version of a recent theory by Apfel⁴, an equation is presented here that correctly predicts the variation of the acoustic cavitation threshold of water with surface tension, dissolved gas content and temperature.