Mechanism for unconventional nonlinear elasticity

Abstract

Materials either have a high hardness or excellent ductility, but rarely both at the same time. Mo2BC is one of the only crystalline materials that simultaneously has a high Vickers hardness and is also moderately ductile. The origin of this unique balance is revealed here using stress-strain calculations. The results show an anisotropic non-linear elastic response including an intermediate tensile strainstiffening behavior and a two-step sequential failure under shear strain that resembles the behavior of soft materials like biological systems or polymer networks rather than hard, refractory metals. The mechanism of the unusual non-linear elasticity is established by analyzing changes in the electronic structure and the chemical bonding environments under mechanical perturbation. The optimized structure under extreme strain shows the formation of a pseudogap in DOS and dimerization of the structure's boron-boron zigzag chain. These mechanisms delay the ultimate failure establishing a new pathway for developing the next generation of structural materials with high hardness and ductility.

Machine Learning for Structural Materials

“…Figure 1b shows the load-dependent Vickers hardness measurement of Mo 0.9 W 1.1 BC, confirming high hardness even at the asymptotic region. The team then followed up with studies to confirm the predicted bulk modulus values, examine lattice strain and texture formation upon loading (27), and explain the chemical origin of the high hardness and surprising ductility in Mo 0.9 W 1.1 BC (28) and other compounds in the chemical series (29). This case study not only is an excellent example of the powerful role that ML can play in the identification of new structural materials, but it also shows how a research project that begins with ML can develop into a grander endeavor.…”

Trends in Bulk Compressibility of Mo2–xWxBC Solid Solutions

“…Furthermore, Mansouri Tehrani et al used stress− strain calculations to investigate the anisotropic, nonlinear elastic behavior of Mo 2 BC and observed tensile strain stiffening along the [001] direction. 32 The observed stiffening was attributed to the formation of an electronic pseudogap within the density of state and the dimerization of the boron− boron chains, delaying shear failure and enhancing ultimate strength and strain. Additionally, the (111)[1̅ 1̅ 2] was identified as the softest shear plane, contributing to the ductility of the structure.…”

“…Lattice preferred orientation was demonstrated along planes parallel to the covalent chains, suggesting that dislocation glide occurs in directions that do not require the breaking of B–B bonds. Furthermore, Mansouri Tehrani et al used stress–strain calculations to investigate the anisotropic, nonlinear elastic behavior of Mo 2 BC and observed tensile strain stiffening along the [001] direction . The observed stiffening was attributed to the formation of an electronic pseudogap within the density of state and the dimerization of the boron–boron chains, delaying shear failure and enhancing ultimate strength and strain.…”

Trends in bulk compressibility of Mo2-xWxBC solid solutions

“…Mansouri Tehrani et al used stress-strain calculations to investigate the anisotropic, nonlinear elastic behavior of Mo 2 BC and observed tensile strain stiffening along the [001] direction. 28 The observed stiffening was attributed to the formation of an electronic pseudogap within the density of state and the dimerization of the boron-boron chains, delaying shear failure and enhancing ultimate strength and strain. Additionally, the (111) [ 11 2] was identified as the softest shear plane, contributing to the ductility of the structure.…”