Application Of Shear Strain Research Articles

Tc and the elastocaloric effect of Sr2RuO4 under 〈110〉 uniaxial stress: No indications of transition splitting

There is considerable evidence that the superconductivity of Sr2RuO4 has two components. Among this evidence is a jump in the shear elastic modulus c66 at the critical temperature Tc, observed in ultrasound measurements. Such a jump is forbidden for homogeneous single-component order parameters, and it implies that Tc should develop as a cusp under the application of shear strain with 〈110〉 principal axes. This shear strain should split the onset temperatures of the two components, if they coexist, or select one component if they do not. Here, we report measurements of Tc and the elastocaloric effect of Sr2RuO4 under uniaxial stress applied along the [110] lattice direction. Within experimental resolution, we resolve neither a cusp in the stress dependence of Tc, nor any second transition in the elastocaloric effect data. We show that reconciling these null results with the observed jumps in c66 requires extraordinarily fine tuning to a triple point of the Ginzburg-Landau parameter space. In addition, our results are inconsistent with homogeneous time-reversal symmetry breaking at a temperature T2≤Tc as identified in muon spin relaxation experiments. Published by the American Physical Society 2024

Homogenization assumptions for the two-scale analysis of first-order shear deformable shells

This contribution presents a multiscale approach for the analysis of shell structures using Reissner–Mindlin kinematics. A distinctive feature is that the thickness of the representative volume element (RVE) corresponds to the shell thickness. The main focus of this paper is on the choice of correct boundary conditions for the RVE. Three different types of boundary conditions, which fulfil the Hill–Mandel condition, are presented to bridge the two scales. A common feature is the application of zero-traction boundary conditions at the top and bottom surfaces of the RVE. Furthermore, an internal constraint is used to reduce the dependency of the stiffness components on the RVE size. The introduced boundary conditions differ mainly in the application of shear strains and their symmetry requirements on the RVE. The characteristic features are compared by means of linear-elastic benchmark tests. It is shown that the stress resultants and tangent stiffness components are obtained correctly. Moreover, the presented approach is verified using different macroscopic shell structures and different mesostructures. Both, linear and nonlinear small strain examples are compared to analytical values or full-scale solutions and demonstrate a wide applicability of the present formulation.

Control of corrosion features by forming parameters

During forming operations, the microstructure of metal parts is usually changed. Effects of cold hardening result in different mechanical properties, whereas the deformed microstructure also changes the electromechanical properties. The latter is responsible inter alia for the chemical corrosion behavior in terms of breakdown potential. In this study, the principle of corrosion resistance of steel E355 (EN 10305-1) was analyzed after rotary swaging with the same nominal strain but different process settings. Especially higher feed rates (forming increments per stroke) and the additional application of shear strain by eccentric rotary swaging increased the pitting potential significantly and thus the corrosion resistance. The introduced methods are assumed as prospective candidates for industrial production of parts that provide higher durability without further anti-corrosion treatment.

Efficient two-level parallelization approach to evaluate spin relaxation in a strained thin silicon film

The evaluation of the spin lifetime in an ultra-thin silicon film is a massive computational challenge because of the necessity of performing appropriate double integration of the strongly scattering momentum-dependent spin relaxation rates. We have tackled the problem by dividing the whole computation range into two levels. Our scheme in each level is based on a hybrid parallelization approach, using the message passing interface MPI and OpenMP. In the first level, the algorithm precalculates the subband wave functions corresponding to fixed energies and archives the results in a file-based cache to reduce memory consumption. In the second level, we compute the spin relaxation time by using the archived data in parallel. This two-level computation approach shows an excellent parallel speedup, and most efficient ways to maximally utilize the computational resources are described. Finally, how an application of shear strain can dramatically increase the spin lifetime is shown.

Vacancy-induced mechanical stabilization of cubic tungsten nitride

First-principles methods are employed to determine the structural, mechanical, and thermodynamic reasons for the experimentally reported cubic WN phase. The defect-free rocksalt phase is both mechanically and thermodynamically unstable, with a negative single crystal shear modulus ${C}_{44}=\phantom{\rule{0.16em}{0ex}}\ensuremath{-}86\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and a positive enthalpy of formation per formula unit ${H}_{f}=\phantom{\rule{0.16em}{0ex}}0.623\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ with respect to molecular nitrogen and metallic W. In contrast, WN in the NbO phase is stable, with ${C}_{44}=\phantom{\rule{0.16em}{0ex}}175\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and ${H}_{f}=\phantom{\rule{0.16em}{0ex}}\ensuremath{-}0.839\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. A charge distribution analysis reveals that the application of shear strain along [100] in rocksalt WN results in an increased overlap of the ${t}_{2g}$ orbitals which causes electron migration from the expanded to the shortened W-W $\ensuremath{\langle}110\ensuremath{\rangle}$ bond axes, yielding a negative shear modulus due to an energy reduction associated with new bonding states 8.1--8.7 eV below the Fermi level. A corresponding shear strain in WN in the NbO phase results in an energy increase and a positive shear modulus. The mechanical stability transition from the NaCl to the NbO phase is explored using supercell calculations of the NaCl structure containing ${C}_{v}=\phantom{\rule{0.16em}{0ex}}0%\ensuremath{-}25%$ cation and anion vacancies, while keeping the N-to-W ratio constant at unity. The structure is mechanically unstable for ${C}_{v}l\phantom{\rule{0.16em}{0ex}}5%$. At this critical vacancy concentration, the isotropic elastic modulus $E$ of cubic WN is zero, but increases steeply to $E=445\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ for ${C}_{v}=\phantom{\rule{0.16em}{0ex}}10%$, and then less steeply to $E\phantom{\rule{0.16em}{0ex}}=561\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ for ${C}_{v}=\phantom{\rule{0.16em}{0ex}}25%$. Correspondingly, the hardness estimated using Tian's model increases from 0 to 15 to 26 GPa as ${C}_{v}$ increases from 5% to 10% to 25%, indicating that a relatively small vacancy concentration stabilizes the cubic WN phase and that the large variations in reported mechanical properties of WN can be attributed to relatively small changes in ${C}_{v}$.

Generating Misorientations in Shear Deformation Structures

Of considerable importance to the generation of ultrafine microstructures is the development of high misorientations. The present work examines the effect of the crystallographic rotation field in simple shear upon the evolution of misorientation during plastic working. A series of Taylor simulations are presented and it is shown that the rotation field is such that small differences in orientation in the region of the main torsion texture components are considerably increased with the application of shear strain. This did not occur in simulations of rolling. The torsion simulations compare favourably with the nature of the misorientations evident in hot worked 1050 Al and Ti-IF steel. It is concluded that shear deformation, by its nature, facilitates the generation of higher misorientations.