(Received 23 October 1984; accepted 14 February 1986)
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Predictions of ground motion and stresses generated by high explosive events are only as good as the constitutive relationships used. Data for stress states in excess of 5 MPa (50 bar) that are reached with strain rates above 102 s−1 are very limited, especially for in situ materials. Three planar and one spherical in situ tests were fired in an attempt to obtain a direct estimation of the constitutive relationships for stresses up to 1 GPa at rapid loading rates. Reduction of the data by inverting the equations of motion in conjunction with the data directly has shown that there is an approximate doubling of the loading constrained modulus when rise times are shorter than 1 ms and stresses are in excess of 30 MPa (0.3 kbar). For the spherical case, peak stresses arrive earlier than peak strains at the higher loading rates. This appears to indicate a severe strength reduction at peak stress. The apparent modulus increase could be due to high shear strengths upon initial loading which become degraded after peak stress passage.
California Research & Technology, Inc., Albuquerque, NM
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