Experimental Investigation of Large-Amplitude Elastic Wave Propagation and the Elastic-Plastic Transition in Polycarbonate (LEXAN).
NORTH CAROLINA STATE UNIV RALEIGH
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An experimental system for determining strain-time and surface rotation-time histories during axial impact of rods is used to investigate the propagation of large-amplitude elastic strain waves and the elastic-plastic transition in polycarbonate Lexan rods. This previously-reported system employs in-surface diffraction grating strain transducers illuminated by a pulsed ruby laser, with the strain and surface rotation-dependent diffraction pattern recorded by high-speed streak cameras. Strain-time histories are obtained for times up to 250 microsec after impact at locations ranging from two to four diameters from the impact site in rods undergoing axial impact at striker velocities of approximately 540 ftsec strains to 8.65 percent and strain rates in excess of 2200 sec-1 are recorded. Strain-time histories at one-third diameter from the impact site at striker velocities ranging up to 700 ftsec reveal that the elastic-plastic transition in Lexan for pulse-type loadings approximately 120 microsec loading- unloading occurs at about 11.5 percent strain, with an abrupt change in the character of the unloading as the transition strain is exceeded strains to 13.3 percent and strain-rates to 15,700 sec-1 are recorded. The effect of a previous impact on the subsequent strain-time history is examined, as well as the relationship between maximum strain and residual strain for strains near the elastic-plastic transition. Author-PL