Ryan A. Austin

TL;DR: In this article, a physically-based model is developed to address slip in polycrystalline metals and alloys subjected to very high rates of deformation (104−108 s−1).

Abstract: A numerical model is developed to study the shock wave ignition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal. The model accounts for the coupling between crystal thermal/mechanical responses and chemical reactions that are driven by the temperature field. This allows for the direct numerical simulation of decomposition reactions in the hot spots formed by mechanical loading. The model is used to simulate intragranular pore collapse under shock wave loading. In a reference case: (i) shear-enabled micro-jetting is responsible for a modest extent of reaction in the pore collapse region, and (ii) shear banding is found to be an important mode of localization. The shear bands, which are filled with molten HMX, grow out of the pore collapse region and serve as potential ignition sites. The model predictions of shear banding and reactivity are found to be quite sensitive to the respective flow strengths of the solid and liquid phases. In this regard, it is shown that reasonable assumptions of liquid-HMX viscosity can lead to chemical reactions within the shear bands on a nanosecond time scale.

TL;DR: In this paper, a mechanistic model of shock-wave-induced viscoplasticity is parameterized for three polycrystalline metals: Cu, Ni, and Al. The model is also extended to higher stress wave amplitudes by incorporating homogeneous dislocation nucleation within the constitutive framework.

TL;DR: System response variability and parameter uncertainty in an empirical model are estimated in a computationally efficient manner to formulate the error margin indices, which are then leveraged to search for ranged sets of design specifications.

TL;DR: Findings point to an increase in suicide rates for patients with schizophrenia, which appear 20-fold higher than previously thought.