Constitutive Relations from 'in situ' Lagrangian Measurements of Stress and Particle Velocity.
Interim rept. on Phase 1,
STANFORD RESEARCH INST MENLO PARK CALIF
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The first phase of a program on in situ measurement of stress waves to obtain more realistic constitutive relations of rocks and soils is described. The equations of motion were transformed for calculating constitutive relations from stress and particle velocity data obtainable with Lagrangian gages in spherical waves. Calculated and exact specific volume-time profiles were compared for a decaying spherical shock wave as a test of the accuracy of specific volume-particle velocity relations determined with particle velocity gages in divergent waves. Ytterbium stress gage systems suitable for in situ measurements were tested on small-scale laboratory experiments. Gages recovered intact after shock loading to about 20 kbar indicated that the gage system was promising for use on large-scale field experiments. The absence of gage stretching signals in hemicylindrical and spherical flow experiments indicates that tangential stress is not transmitted to the gage element. Various existing and proposed particle velocity gage systems were examined for accuracy and for adaptability to in situ work. Mutual inductance and self-inductance and microwave reflection systems were examined. A proposed mutual inductance system appeared to be most suited to in situ experiments. Author