Shock Waves and High-Strain-Rate Phenomena in Metals

Originally published by Shock Waves and High-Strain-Rate Phenomena in Metals, Mark A. Meyers and Lawrence E. Murr (eds.), Plenum Press, New York (1981), pp. 675-702.

Authored by Allan H. Clauer, John H. Holbrook.

A high-energy, pulsed laser beam combined with suitable transparent overlays can generate pressure pulses of up to 6 to 10 GPa on the surface of a metal. The propagation of these pressure pulses into the metal in the form of a shock wave produces changes in the materials microstructure and properties similar to those produced by shock waves caused in other ways. This paper reviews the mechanism of shock wave formation, calculations for predicting the pressure pulse shape and amplitude, in-depth microstructural changes and the property changes observed in metals. These property changes include increases in hardness, tensile strength and fatigue life. The increases in fatigue life appear to result from significant residual surface stresses introduced by the shock process.

INTRODUCTION
The ability of a high-energy, pulsed laser beam to produce recoil pressures from vaporization of metal surfaces was suggested in 1963 by Askaryon and Morez (1). Others verified this effect on unconfined surfaces (2-4). Then Anderholm (5) showed that pressures of gigapascals (GPa) could be obtained at confined surfaces, i.e., surfaces covered by an overlay transparent to the laser beam. This configuration confined the vaporized materials in the vicinity of the metal surface and significantly increased the peak pressures developed. Later, O’Keefe and Skeen (6) investigated the effects of several different transparent overlays and Yang (7) measured the peak pressures developed by a large number of metal absorbers using a glass transparent overlay. Fairand et al (8) and Fairand and Clauer (9) showed comparisons between pressure measurements and calculated pressures including the effects of different transparent overlays and target absorber materials.

Based on the early demonstrations of the potentially significant stress waves developed in metals by high energy pulsed laser beams, Fairand et al (11) showed that beneficial property and microstructural changes could be produced in an aluminum alloy. The success of these first experiments led to the further exploration and development of laser peening of metals. This paper reviews all the aspects of laser shock processing: the formation mechanism of the stress waves, calculations for predicting the pressure environment, in-depth microstructural effects and the material property changes which have been observed up to this point in the process development.

To download the entire article- as a pdf: Effects of Laser Induced Shock Waves on Metals