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Atomistic-model informed pressure-sensitive crystal plasticity for crystalline HMX

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Cyclotetramethylene-Tetranitramine (HMX) is a secondary explosive used in military and civilian applications. Its plastic deformation is of importance in the initiation of the decomposition reaction, but the details of plasticity are not yet fully understood. It has been recently shown that both the elastic constants and the critical resolved shear stress for plastic deformation are pressure sensitive. Since initiation takes place during shock loading, the pressure sensitivity of plasticity is highly relevant. In this work, we examine the pressure-sensitivity of the dynamic mechanical behavior of HMX. To this end, we use an elastic-plastic continuum constitutive model of single crystal HMX in which the anisotropic elastic constants and direction-dependent yield stress are rendered pressure-sensitive. The pressure sensitivity is calibrated based on input from molecular models. We observe that accounting for pressure sensitivity changes significantly the profile of the elastic-plastic wave and the wave propagation speed upon impact. The accumulated dissipation profile and the total dissipation also exhibit profound differences between the simulations that take account of the pressure-dependence of the plastic deformation and the pressure independent counterpart. 2 Ran Ma et al.
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... The advantage is a higher fidelity description of the elastic response, but doing so for a material under shock conditions requires knowledge of the pressure and temperature dependence of the elastic coefficients, which in most cases is only available from simulations [15]. Furthermore, the possibility of coupling between the volumetric and deviatoric responses may make it difficult to frame a proper inverse problem for experiments [16][17][18]. ...
... 18: Comparison of black-box neural network architectures trained on monolithic data with our Hamilton-Jacobi hardening elastoplastic framework (introduced in Section 3.2). The black-box models can capture the monolithic loading path (a) but cannot capture any unloading paths (b). ...
... 18: Comparison of hybrid model predictions with FFT simulation data for 3 RVEs from the training data set. The tests conducted are uniaxial unconfined tension (left and middle columns) and pure shear (right column). ...
... The advantage is a higher fidelity description of the elastic response, but doing so for a material under shock conditions requires knowledge of the pressure and temperature dependence of the elastic coefficients, which in most cases is only available from simulations . Furthermore, the possibility of coupling between the volumetric and deviatoric responses may make it difficult to frame a proper inverse problem for experiments (Borja, 2013;Bryant and Sun, 2018;Ma et al., 2021). ...
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