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Experimental study of strain wave propagation in quarter-hard electrolyic copper bars Anderson, Clifford John

Abstract

Specimens of quarter-hard electrolytic copper, twenty feet in length and one-quarter inch in diameter, were statically pre-stressed and subjected to impact loading. Dynamic strain vs time traces, for both loading and unloading waves, were obtained using resistance-type strain gages mounted at various positions along the specimens. Permanent strain increments resulting from each impact were determined. Prestress levels ranged from values well below the yield point of the material to values exceeding the yield point. Impact velocities and impact durations were also varied. The experimental strain wave shape and propagation velocity in bars prestressed well below the yield point were found to compare favorably with the theoretical elastic wave shape and velocity. The unloading waves propagated in bars prestressed above the yield point were found to be similar in shape to the elastic waves observed and to propagate at the elastic velocity without diminution of amplitude. For loading waves propagated in material prestressed above the yield point the incipient portion of plastic strain waves was found to propagate at the elastic velocity. The lower strain increments of the plastic strain waves were found to propagate at higher velocities and the highest strain increments were found to propagate at lower velocities than would be predicted from a strain-rate-independent theory. For the loading waves, a method was developed to approximate the dynamic loading curves (stress-strain relation followed during impact loading). Prom the dynamic loading curves, the peak stress levels of the plastic strain pulses were found to be significantly higher than the stresses at equivalent strains on the static stress-strain curve. The results tended, at least qualitatively, to support a strain-rate-dependent wave propagation theory rather than a strain-rate-independent one.

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