Effect of Heat Treatment on the Cyclic Deforming Behavior of As-Extruded ZA81M Magnesium Alloy

In the present work, the effect of heat treatment on the cyclic deformation behavior of as-extruded ZA81M magnesium alloy was investigated. Two heat treatment conditions were applied to the as-extruded ZA81M alloy: a solution treatment (T4, 653 K for 40 h and quenched with 298 K water) and a solution treatment plus artificial aging (T6, 348 K for 32 h (pre-aging at low temperature) and 453 K for 8 h (the second aging) and quenched with 353 K water). The results showed that the fine second phase precipitated after the aging treatment, the tensile yield strength of the T6-treated specimens increased, and the stress amplitude of T6-treated specimens was always higher than that of T4-treated specimens. The T6-treated specimens had a higher total strain energy density and a shorter fatigue life at a strain amplitude of 0.4%, and a lower total strain energy density and a longer fatigue life at a strain amplitude of 0.8%, compared to the T4-treated specimens. All fatigue cracks of the T4 and T6 ZA81M alloy were initiated at the second phase or along the grain boundary and propagated perpendicular to the loading direction.

Atomistic Study on the Mechanical Behavior of Silicon-Base Nanotubes

Recently, silicon nanotubes (SiNTs) have been successfully synthesized and have attracted many researchers to work on the different aspects of them. In the present study, the stress-strain curve along with the Young’s modulus as a significant mechanical property of single walled silicon nanotubes at different diameters are determined. The simulation is performed by the use of molecular dynamics based on the Tersoff-Brenner many-body potential energy function. The results of the total strain energy of nanotubes as an accurate and effective methodology are used to establish appropriate expressions for evaluating Young’s modulus of the nanotubes.

Effect of pre-corroded on fatigue behavior of MAO treated ZK60 magnesium alloy in a simulated body fluid

A bio-ceramic coating was prepared on the surface of ZK60 magnesium alloys by micro-arc oxidation (MAO) method. The substrate (BM) and coated (MAO) specimens were pre-corroded in a simulated body fluid (SBF) for 12 h. Strain-controlled and stress-controlled loading modes were used to conduct fatigue tests for the two specimens, respectively. The cyclic deformation behavior of the two specimens with non-corroded and pre-corroded was studied. The mechanism of cyclic deformation under different loading conditions is related to twinning and slip. At the same test conditions, the fatigue life of the non-corroded BM specimen is higher than that of the non-corroded MAO specimen, while the fatigue life of the pre-corroded MAO specimen is higher than that of the pre-corroded BM specimen. A modified total strain energy model is proposed and the precision of life prediction is higher than that of traditional fatigue model.

Ligand Strain Energy in Large Library Docking

ABSTRACTWhile small molecule internal strain is crucial to molecular docking, using it in evaluating ligand scores has remained elusive. Here, we investigate a technique that calculates strain using relative torsional populations in the Cambridge Structural Database, enabling fast pre-calculation of these energies. In retrospective studies of large docking screens of the dopamine D4 receptor and of AmpC β-lactamase, where close to 600 docking hits were tested experimentally, including such strain energies improved hit rates by preferentially reducing high-scoring decoy molecules that were strained. In a 40 target subset of the DUD-E benchmark, we found two thresholds that usefully distinguished between ligands and decoys: one based on the total strain energy of the small molecules, and one based on the maximum strain allowed for any given torsion within them. Using these criteria, about 75% of the benchmark targets had improved enrichment after strain filtering. Relying on pre-calculated population distributions, this approach is rapid, taking less than 0.04 second to evaluate a conformation on a standard core, making it pragmatic for pre-calculating strain in even ultra-large libraries. Since it is scoring function agnostic, it may be useful to multiple docking approaches; it is openly available at http://tldr.docking.org

An Experimental Method for Estimating the Tearing Energy in Rubber-like Materials Using the True Stored Energy

A method for determining the critical tearing energy in rubber-like materials is proposed. In this method, the energy required for crack propagation in a rubber-like material is determined by the change of the recovered elastic energy. Hence, the dissipated energy due to different inelastic processes is deducted from the total strain energy applied to the system. Therefore, the classical method proposed by Rivlin and Thomas using the pure shear tear test is modified using the actual stored elastic energy. The elastically stored energy in a pure shear is determined experimentally using cyclic loading under quasi-static loading rate of 0.01 s-1 for different unloading rates, i.e. 0.01, 0.1 and 1.0 s-1. The experimental results show that the classical method overestimates the critical tearing energy by approximately 18% and the unloading rate is minimal which suggests that the dissipation depends only on the loading path.

Analysis of Multi-Stable Architectures for Morphing Structures

The field of multi-stable structures has been steadily growing due to a wide range of potential applications including energy harvesting, MEMS, and mechanical logic. This work focuses on utilizing elastic energy trapping and snap-through phenomena of bistable unit cells to design a latticed, hierarchical multi-stable cylinder that can articulate up to 30 degrees from its center axis. The employment of bistable elements is hypothesized to reduce the total strain energy required to articulate the cylinder, and yield faster responses with the snap-through. While multi-stable cylinders exist in previous studies, there have been no previous attempts at studying different modes of deformation beyond compressive loading. Thus, the current work presents a new problem regarding the effects of bistable elements in a latticed cylinder that is carrying tensile, compressive, and shear loadings and exhibiting large displacements as the cylinder is articulated.. The total strain energy density of the articulating cylinder is investigated as a function of the heights of the unit cells, which aids in determining an ideal height for the design that minimizes the strain energy density. Results show that the strain energy of an articulating cylinder can be minimized with the use of multi-stability, and that a multi-stable cylinder can require up to three times less loads to maintain desired articulation compared to a mono-stable structure. These results will lead to future works on further optimizing the articulating cylinder by varying additional parameters like the individual heights of rows, the thicknesses of unit cell beams, the strain energy density, and the initial loading threshold for articulation. In addition, the work in this study can yield methodologies for designing arbitrarily morphing skins beyond just cylindrical geometries.

A note on the volumetric-deviatoric split on the anisotropic constitutive model for fiber-reinforced materials

In the literature, it has been suggested that for a class of anisotropic constitutive laws for fiberreinforced materials, the volumetric-deviatoric split should only be performed on the isotropic (matrix) term, but not on the anisotropic (fiber) term. In this research note, we follow up on the theoretical and numerical analyses adopted in these early publications with an intuitive example that allows us to directly analyze the effect of this split. We demonstrate that performing such split on the anisotropic term leads to non-physical volume growth of the material sample. Therefore, we consolidate the observation that the volumetric-deviatoric split should not be applied to the anisotropic (fiber) term of the total strain energy.

Low Cycle Fatigue Life Prediction Model of 800H Alloy Based on the Total Strain Energy Density Method

In this paper, a high-temperature low-cycle fatigue life prediction model, based on the total strain energy density method, was established. Considering the influence of the Masing and non-Masing behavior of materials on life prediction, a new life prediction model was obtained by modifying the existing prediction model. With an 800H alloy of the heat transfer tube of a steam generator as the research object, the high-temperature and low-cycle fatigue test was carried out at two temperatures. The results show that the predicted and experimental results are in good agreement, proving the validity of the life prediction model.