Abstract
When metal is subjected to extreme strain rates, the conversation of energy to plastic power, the subsequent heat production and the growth of damages may lag behind the rate of loading. The imbalance alters deformation pathways and activates micro-dynamic excitations. The excitations immobilize dislocation, are responsible for the stress upturn and magnify plasticity-induced heating. The main conclusion of this study is that dynamic strengthening, plasticity-induced heating, grain size strengthening and the processes of microstructural relaxation are inseparable phenomena. Here, the phenomena are discussed in semi-independent sections, and then, are assembled into a unified constitutive model. The model is first tested under simple loading conditions and, later, is validated in a numerical analysis of the plate impact problem, where a copper flyer strikes a copper target with a velocity of 308 m/s. It should be stated that the simulations are performed with the use of the deformable discrete element method, which is designed for monitoring translations and rotations of deformable particles.
Highlights
Metals subjected to extreme dynamics experience rapid microstructural evolution
When energy is delivered to metals with rates faster than the rate at which the energy is converted to plastic work and damages, there is uncompensated energy, which is partly stored in the newly created dislocation structures and the rest of it activates micro-dynamic excitations
In the Taylor–Quinney interpretation, a significant portion of plastic work is converted to heat [6,7,8,9], while the remaining work is stored in dislocation structures
Summary
Metals subjected to extreme dynamics experience rapid microstructural evolution. Dislocations are generated, become entangled and form fine structures [1]. Brown [25] offered an interesting idea that plastic flow is responsible for the formation of dislocation structures in the state of self-organized criticality. The macroscopic plastic flow H results from slip events along many θ planes defined number of grains and, grain-to-grain misorientations, there ismisoriented a much larger by two orthogonal unit given vectors, nθ and sθ. 2 −π/4 the trend.∂tThe dominant slip plane is defined in terms of two orthogonal unit vectors and and the flow tensor is a dyadic product of the two d. The dominant slip plane is defined in terms of two orthogonal unit vectors nσ and sσ and the flow tensor is a dyadic product of the two N = (nσ sσ + sσ nσ ). The rate of damage is controlled by the parameter q
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