No abstract

No abstract

In this article we develop a theory of spallation of a brittle thermoelastic body, and of the interaction between propagating waves and accumulated damage. This theory is applied to the prediction of the effect of spall damage on the elastic stiffness and thermal conductivity of the material.

No abstract

Following the introduction of the concept of continuous spall damage as a replacement for the customary discrete description, existing spall criteria are generalized to continuous measures of damage and are classified according to their dependence on the history of the continuum field variables. A compound-damage-accumulation theory is proposed in which the rate of damage accumulation depends on the existing damage, in addition to the applied stress. Several examples of the application of the new theory to the correlation of existing data are given.

High-purity monocrystalline aluminum disks of three crystallographic orientations were subjected to carefully controlled planar impact producing low levels of spall damage. This damage was observed by optical and scanning electron microscopy of sections through the recovered disks, and was found to consist of voids of essentially octahedral form having {111} planes as faces. To describe the growth of these voids we propose a kinematical model based on the motion of edge dislocations. Dynamical equations describing the rate of growth of an individual void are obtained by applying established concepts of dislocation mechanics to the kinematical model. Finally, the dynamical void growth model is combined with an empirically established nucleation model to yield equations for calculating the total volume growth rate in a spalling sample. Extension of these results to other ductile fracture phenomena is suggested.

No abstract

In this paper several variations of a simple theory of dynamic compaction of porous solids are presented and discussed. This theory elaborates the conventional theory of shock propagation in such a way that the shock structures observed to propagate in these materials can be described. Steady-wave profiles are calculated for several compaction models, and the inference of constitutive equations from experimental data is discussed. It is shown that the theory can be made to reproduce steady-wave profiles observed in the usual plate-impact experiments exactly.