The tensile stress results were very encouraging. The lower strength conditions (i.e. solution treated and quenched and T73) both showed higher strength after laser peening. The stronger, peak aged T6, condition showed a slightly diminished strength. This difference could be easily explained by the dislocation substructures produced by laser peening. The cold worked microstructures added strength to the weaker alloys having either no significant dispersed precipitates as in the solution treated condition, or a coarser dispersion of precipitates as in the T73 condition. However, in the case of the T6 condition, peak aged to have an optimum dispersion of fine precipitates, the strengthening effect of the cold worked structure was less than that of the dispersion strengthening. The higher density of somewhat mobile dislocations in the laser peened T6 condition may actually have had the effect of slightly lowering the yield strength.
Based on this promising demonstration that laser peening could indeed have a significant effect on metal properties, the National Science Foundation supported a multi-year project at Battelle to pursue in-depth exploratory research into the effects of laser shock waves on metals.
It is clear from the events, that if any one of them had not occurred, laser shock peening would not have been known or pursued until sometime in the 1980s or perhaps not until the mid-1990s based on the successful development of small spot peening by Dr. Yuji Sano in Japan.
The first published paper on laser shock peening of metals presented the results of the above experiments.
See the Reference: B.P. Fairand, B.A. Wilcox, W.J. Gallagher and D.N. Williams, Laser Shock-Induced Microstructural and Mechanical Property Changes n 7075 Aluminum, J. of Applied Physics, Vol. 43, No. 9, PP. 3894-3895 (1972).
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