A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

Heat generation in the vicinity of a void during shock compression plays a key role in the initiation of energetic materials. The shock response of a single β ‐HMX crystal with a single void is studied with simulations that include plasticity and heat transport. The numerical results are validated with an experiment in which a 500 μ m void is machined in an HMX single crystal and impacted. Experiments and simulations of the dynamical evolution of the morphology of the void during the collapse and the rate of the area are in very good agreement for weak shocks.

“…where

N_{s}

is the number of slip systems and

{\dot{γ}}_{s_{i}}

is the slip rate on the slip system

s_{i}

. Following the work in references the elastic part of the deformation gradient is decomposed multiplicatively into isochoric

F {^{'}}_{e}

and volumetric

F_{e}^{v}

parts:

true F_{e} = boldF {^{'}}_{e} F_{e}^{v}

…”

Section: Constitutive Modelmentioning

confidence: 99%

Void Collapse in Shocked ‐HMX Single Crystals: Simulations and Experiments

Duarte

Hamed

Drake

et al. 2020

“…The Helmholtz free energy is assumed to take the form (cf. )

true ρ_{0} ψ = ρ_{0} ψ_{eos} ((), V, T) + 0false \frac{1}{2} ϵ : ℂ ((), P) : ϵ - 0false \frac{1}{2} K ((), P) ϵ_{normalV}^{2}

…”

Section: Theory and Modelingmentioning

confidence: 99%

“…These include equation of state , elastic constants , thermal expansion coefficients , driving forces for phase transformations , surface energies, and may potentially help identify deformation mechanisms. On the other hand, the behavior of the constituents under dynamic conditions must still be determined from carefully designed experiments .…”

Section: Introductionmentioning

confidence: 99%

Interpreting Experimental Results from Shock Impacts on Single Crystal PETN in the Context of Continuum Models

Luscher

Cawkwell

Ramos

et al. 2019

In this paper we interpret previous experimental measurements of impacts on single crystal PETN in the context of a simple continuum model. Hugoniot calculations using the simple model framework under various limiting assumptions envelope measured Hugoniot states reasonably well and suggest that non‐negligible deviatoric elastic strains may exist in the shock compressed state for weak impacts. An accompanying simple kinematic model for lattice deformation was used to estimate the expected shifts in X‐ray diffraction peaks for the (211) plane under impacts normal to (110) planes. The results suggest that negligible relaxation of the deviatoric lattice deformation occurs on the short (10–20 ns) time and wave propagation (40–80 m) scales of laser‐driven shock experiments, and that the corresponding elastic strains may be large. Because of the potentially large deviatoric elastic strains, the specific finite deformation strain measure used within thermomechanical single crystal models is of significant consequence, which is explored numerically by the comparison of isothermal purely elastic responses under uniaxial and simple shear deformations.

“…They calibrated the model against wave profiles of (111) and (210) orientations. Luscher et al [23] also developed an anisotropic dislocation-based, high strain rate model for RDX single crystals and calibrated by wave profiles from four orientations of RDX single crystals at various loading conditions. While the model can well capture the distinct anisotropic wave profiles, the experimental wave profiles from different sources contain lots of uncertainty arises from different anvil and window materials, loading configurations, different batches of samples, etc., which complicates the determination of parameters.…”

Section: Introductionmentioning

confidence: 99%

An Anisotropic Elastoviscoplasticity Model of Thermomechanical Responses of Shocked β‐HMX and α‐RDX Single Crystals

Wang

Huang

et al. 2019

An anisotropic elastoviscoplasticity constitutive model for β‐cyclotetramethylene tetranitramine (β‐HMX) and α‐cyclotrimethylene trinitramine single crystals (α‐RDX) is developed to analyze the thermomechanical responses under shock loading. The model considers nonlinear, pressure and temperature dependent elasticity, and dislocation‐based plasticity which incorporate regenerative multiplication and heterogeneous nucleation mechanisms. The proposed model is calibrated against experimental wave profiles of (011), (010), (100), (1‾11) , (011‾) and (111‾) orientations of HMX single crystals and (210), (100), (111‾) , (21‾0) and (111) orientations of RDX single crystals. The model can well capture elastoplastic double wave structure, stress relaxation after the Hugoniot elastic limit as well as the arrival of plastic wave. Moreover, pressure, accumulated shear strain, and temperature contours of both HMX and RDX show obvious anisotropy and non‐uniform spatial distribution, which is explained by analyzing dislocation activity with corresponding resolved shear stress on slip systems. Results provide insights into understanding ignition mechanisms and predicting ignition sensitivity of explosive single crystals as well as polymer bonded explosives at the mesoscale.