STRESS WAVE PROPAGATION IN A PRESTRESSED MEDIUM.
Final rept. 1 Jun 66-31 Jul 67,
STANFORD RESEARCH INST MENLO PARK CALIF POULTER LABS
Pagination or Media Count:
Explosion-induced radiation patterns in prestressed plates which represent two-dimensional models of explosions in the prestressed earth were studied. Radial explosive sources were detonated in plates of 18 in. thick glass and 18 in. and 116 in. Plexiglas prestressed in either tension or shear to various stress levels static principal stresses were on the order of 100 bars. Radiation patterns of the resulting plate compressional and plate shear waves were observed using dynamic photoelasticity employing high speed photography or using electrical strain gages employing high speed, single-sweep oscillography. The measured compressional and shear velocities in Pyrex glass were 5.34 and 3.32 mmmicrosec, and in Plexiglas they were 2.31 and 1.33 mmmicrosec which agree closely with published data. Although compressional and shear waves were clearly optically resolved, no azimuthal variation was seen with compressional or shear wave radiation patterns in spite of strong preferential cracking in the case of prestressed glass. This is because the photoelastic patterns resulted from superposition of a high static approximately 100 bars and relatively low dynamic approximately 10 bars stress. By contrast, radiation patterns recorded with the strain gages in Plexiglas indicated a sharp maximum in shear wave amplitude and possibly a slight maximum in compressional wave amplitude at approximately 30 degrees from the tensile axis. The ratio of the maximum longitudinal to maximum shear wave strain energy had a consistent minimum, the ratio decreases by a factor of 10 to 100 at 30 degrees from the tensile axis. Author
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