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Abstract The strength of rock is related with its viscosity under shock loading. Experimental results show that viscosity of rock at mesolevel is inversely proportional to strain rate under shock loading. The mesostructural aspects of mechanism of decrease of viscosity with growth of strain rate are investigated. It is shown that mesolevel decrease of viscosity with growth of strain rate is related with rotational mode of motion of particles of materials. When the width of shock wave front and size of particles of medium satisfy certain conditions，rotational mode of motion of particles will take place. When the conservation law of moment of momentum is satisfied approximately at mesolevel，the most possible variant is that two neighboring particles rotate oppositely and form conjugate pairs. The two particles of conjugate pairs rotate in opposite direction. With the growth of strain rate，more and more conjugate pairs will appear. The velocity of relative motion between the particles of conjugate pairs is low，and consequently the viscosity is low. In a word，the decrease of viscosity with growth of strain rate lies in activation of internal degrees of freedoms and the emergence of correlated motion of particles of materials under strong dynamic loading.
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Received: 18 April 2007
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