The Influence of High-Rate Deformation on Structure and Properties of Materials in the Presence of Stress Concentrators

Summary

The propagation of shock waves in solid bodies is observed. The equipment and methods of measuring dynamic properties in wide temperature /up to 1200°C/ and strain rate /ε̄ = 104 sec-1/ intervals are worked out. Changes of the deformation mechanism with increasing ε̄ are investigated on the model materials of copper and magnesium alloy.

It is established that with increasing strain rate up to dynamic loads /ε̄ = 104 sec-1 and more/ the transition to a multiple slip occurs. In plastic flow takes place as a result of slip in a great number of slip planes of the 111 <11̄0> system, in the magnesium alloy alongside with basal slip a non-basal one in the (101̄0), (101̄1) systems occurs.

In the magnesium alloy twinning is also activated. Under the conditions of dynamic loading twinning occurs in many systems simultaneously.

Taking into account the deformation characteristics of the materials: A dislocation type, stacking-fault energy, it is possible to describe changes in the deformation mechanism with increasing strain rates.

The change of a dislocation structure has been studied at increasing strain rates. Dislocation density increases 2–3 times as much at increasing strain rate by 6–7 orders of magnitude. The given result points at the fact that a high-rate deformation accomplishes at the expense of the increase in strain rates rather than in their number. The obtained results allow to give a structural explanation of the dynamic properties of the material and to explain an effect of stronger hardening of materials after impulsive loading.

The change of dynamic properties of the materials and their influence on the effect of stress concentration in real constructions are analyzed. The role of stress concentrators depending on a strain rate changes non-monotonously. At the calculation of details working at dynamic loading it is necessary to take into account both changes of properties and structure of materials and of the role of stress concentrators with strain rates.