Tensorial stress−strain fields and large elastoplasticity as well as friction in diamond anvil cell up to 400 GPa

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.

Phase transformations, fracture, and other structural changes in inelastic materials

“…The in situ quantitative synchrotron X-ray diffraction investigation of plastic strain-induced α − ω PT in Zr was performed in [375]. The most consistent results were obtained for strongly plastically predeformed Zr, when strain hardening saturates and material hardness and yield strength and microstructure do not evolve with further plastic deformation [87,236,305,435]. Polycrystalline materials for this case behave like perfectly plastic and isotropic with plastic strain history independent surface of perfect plasticity [236].…”

“…Combined Coulomb and plastic friction between sample, diamond, and gasket were considered. Without PTs, elastoplastic models were calibrated and verified by independent experiments for rhenium [101,103,104] and tungsten [305] up to 300 GPa and 400 GPa, respectively. Various experimental phenomena have been reproduced and explained, some have been predicted, methods of controlling PTs were suggested, and some possible misinterpretations of experimental results have been demonstrated, see [246,252].…”

“…( 161) for strain-induced PT was implemented as well. Third-and fourth-degree anisotropic elastic energy were utilized for diamond [103,305]. Combined Coulomb and plastic friction between sample, diamond, and gasket were considered.…”

Nonlinear elasticity of prestressed single crystals at high pressure and various elastic moduli

“…( 156) can be used to find pressure-dependent elastic moduli for polycrystalline aggregates. They also can be used to calibrate some nonlinear isotropic potentials, like Murnaghan potential ( [59,68]), which is broadly used for simulation of deformation processes under high pressure (e.g., [4,5]). Murnaghan potential possesses 5 elastic constants, four of which, bulk and shear moduli and their pressure derivatives can be found from elastic moduli of single crystals and their pressure derivative.…”

“…Elastic moduli under high pressures play a fundamental role for the solution of numerous basic and applied problems. These problems include determination of tensorial stress-strain relationships for single and polycrystalline aggregates, which are utilized for continuum simulations of deformation of material under extreme dynamic [1][2][3] or static [4,5] loadings. Nonlinearity of the elasticity rules lead to elastic instabilities [6][7][8][9][10].…”