Abstract
Various phenomena (fracture, phase transformations, and chemical reactions) studied under extreme pressures in diamond anvil cell are strongly affected by fields of all components of stress and plastic strain tensors. However, they could not be measured. Here, we suggest a coupled experimental−theoretical−computational approach that allowed us (using published experimental data) to refine, calibrate, and verify models for elastoplastic behavior and contact friction for tungsten (W) and diamond up to 400 GPa and reconstruct fields of all components of stress and large plastic strain tensors in W and diamond. Despite the generally accepted strain-induced anisotropy, strain hardening, and path-dependent plasticity, here we showed that W after large plastic strains behaves as isotropic and perfectly plastic with path-independent surface of perfect plasticity. Moreover, scale-independence of elastoplastic properties is found even for such large field gradients. Obtained results open opportunities for quantitative extreme stress science and reaching record high pressures.
Highlights
In static high-pressure research, megabar pressures are generated by compression of a thin sample by two diamonds in diamond anvil cells (DAC)[1,2,3,4]; see Fig. 1
This process is accompanied by large plastic deformation of a sample and large elastic deformation of the diamond.[5,6]
A complete system of equations for fourth-order elasticity of diamond, large elastoplastic deformation of W, combined Coulomb and plastic friction, geometry of DAC, formulation of axisymmetric problem in cylindrical coordinates rzθ, and nonlinear elastic properties are presented in the Methods section
Summary
In static high-pressure research, megabar pressures are generated by compression of a thin sample by two diamonds in diamond anvil cells (DAC)[1,2,3,4]; see Fig. 1. While essential improvement in reproducing pressure distribution in comparison with the previous works[26,27] was achieved, obtained mechanical properties cannot be considered as verified, and corresponding stress and plastic strain tensor fields may contain significant inaccuracies. Physics-based models for elastoplastic behavior and contact friction should be iteratively developed and refined, and all material properties should be calibrated by fitting to some experimental fields and verified by comparison with other experimental fields. With these properties, simulations provide all fields, including components of the stress and plastic strain tensors, friction stress, etc., i.e., those which cannot be directly measured. All unknown material parameters are calibrated using one set of experimental data and verified using another experimental set
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