Strain Energy Effects Research Articles

Effect of elastic strain energy on precipitation process of Co81Al5V14 alloy based on microscopic phase field method

The L12 phase volume fraction, size, microstructure significantly influences alloy's important physical and mechanical properties in Co-Al-V superalloy. Based on microscopic phase field method and microelasticity theory, precipitation of ordered L12 phase in Co81Al5V14 alloy were studied. The results indicate that precipitation sequence of Co81Al5V14 alloy is minimally influenced by elastic strain energy and precipitation sequence can be divided into four stages. Elastic strain energy does not significantly affect incubation period of alloy, but it does promote the formation of transitional ordered phase L10 with a single orientation and facilitates precipitation of ordered phase L12. Elastic strain energy causes precipitates to grow and coarsen along specific elastic "soft" direction ([100] and [001]). Elastic strain energy promotes process of ordering and atomic occupancy of the alloy. The effects of elastic strain energy on precipitation mechanism, microstructure and atomic occupancy are discussed in this work, which provides theoretical guidance for the design of Co-Al-V alloys with better properties.

Control of the preferential orientation and properties of HiPIMS and DCMS deposited chromium coating based on bias voltage

This study investigates the effects of varying bias voltages on the crystallographic orientation and properties of DCMS + HiPIMS-deposited chromium coatings. Under bias voltages varying from 100 to 500 V, dense Cr coatings were obtained, and the deposition rate decreased by 13 %. The bias voltage significantly impacts the hardness, crystallographic orientation, electrical conductivity, and bonding strength of the coating. As the bias voltage increases, the hardness of the Cr coating gradually increases. The crystallographic orientation of the coating is governed collectively by surface energy, strain energy, and sputtering effects. The preferential crystallographic orientation of the Cr coating transitions from (222) to (110), subsequently changing to a mixed preferential crystallographic orientation of (110), (211), and (222). Under the combined influence of thermal effects and ion bombardment, a (110) preferential crystallographic orientation was obtained at a bias voltage of 300 V, featuring moderate hardness and optimal wear resistance. This study establishes that the electrical characteristics of the coatings have a significant correlation with bias voltage levels.

Mechanical behavior of nanocircular plates under coupled surface and nonlocal effects by using molecular dynamics simulations

The equations of control for a circular thin plate under simple support are obtained by coupling the surface effect and non-local effect using the equilibrium method. Molecular dynamics simulations were used to calculate the residual surface strain energies at different crystal orientations. Different crystal orientations of the same material would affect its surface energy and thus result in different mechanical behaviors. The effects of residual surface strain energy and non-local parameters on the mechanical behavior of circular thin plates were analyzed. The analysis reveals that the surface effect and non-local effect on the deflection of the nanoplates are significant. The surface effect parameter of tensile stress increases the deflection, while the opposite is true for the surface effect parameter of compressive stress, and the non-local parameter decreases the deflection. The influence of surface effect and non-local effect is significant for smaller thicknesses and weakens for larger thicknesses.

A homogenized model for free vibration analysis of finite phononic crystal rods using strain gradient theory

While extensive research has been conducted on elastic wave propagation in infinite phononic crystal (PC) rods, practical applications often involve PC rods of finite length. Therefore, it is essential to consider not only their functional properties, such as wave filtering, but also their mechanical behavior, including free vibration. Motivated by this concern, this study aims to establish a homogenized model for a finite-length PC rod based on the strain gradient theory (SGT) and provide simple closed-form expressions for its natural frequencies. To achieve this objective, an innovative method is developed to determine the material length scale parameters within the SGT. The investigation begins by analyzing the propagation of longitudinal waves in an infinite PC rod. By using the dispersion obtained from Bloch’s theorem as a benchmark, it is demonstrated that the material length scale parameters associated with strain energy and micro-inertial effects in the SGT can be effectively determined by fitting the dispersion obtained from the SGT to the benchmark dispersion obtained from Bloch’s theorem. With the determined parameters, the study proceeds to investigate the free vibration of a finite PC rod. The natural frequencies obtained from both the classical continuum theory (CCT) and the SGT are compared with those calculated by finite element (FE) simulations, which are based on an actual periodic structure and serve as a reliable benchmark. This comparison clearly highlights the superiority of the developed mesoscopic model based on the SGT in accurately predicting the natural frequencies, particularly for higher-order modes, compared to the CCT.

Evolution from gas outburst to coal outburst: An analysis from the perspective of asynchronous transfer difference of gas mass and coal deformation

Considering that coal and gas outburst is a highly complex nonlinear process, the synchronous energy criterion based on the gas expansion energy and the coal deformation potential energy is often adopted to evaluate the hazard. However, the synchronous energy criterion without considering the transfer difference of gas mass and coal deformation has defects in describing the evolution characteristics of coal-rock gas dynamic disasters. Hence, it is necessary to investigate the asynchronous characteristics of the gas expansion energy and the coal deformation potential energy. In this study, the deformation characteristics of coal injected with He and CH4 were measured respectively with the aid of a self-developed device for observing the asynchronous characteristics of effective stress and adsorption-induced deformation. Besides, the differentiated propagation characteristics of gas pressure and adsorption-induced deformation were obtained, and the asynchronous propagation starting point and propagation rate difference between them were analyzed and determined. Furthermore, based on the calculation formula of gas expansion energy and coal deformation potential energy, the values and propagation differences of the two types of energy at different times were revealed. Finally, the typical outburst phenomena were explained using the energy asynchronous theory. The following research findings were yielded. The adsorption-induced expansion process lasts longer than the gas pressure reduction process, which is the reason for asynchronous propagation of gas expansion energy and coal deformation potential energy. The coal deformation potential energy can be further divided into mechanical compression strain energy and desorption shrinkage strain energy. In the initial stage of outburst, the main sources of energy are free gas expansion energy and mechanical compression strain energy. As time progresses, the effect of desorption gas expansion energy and desorption shrinkage strain energy gradually strengthens. From the perspective of energy asynchrony, outburst occurrence at a low gas concentration in deep regions and delayed outburst in cross-cut coal uncovering can be explained as the result of dynamic load instability in surrounding stopes brought about by lagging superimposed deformation disturbances after gas desorption, or the result of self-induced lagging shrinkage deformation formed under special boundary conditions. The findings of this study are helpful to guide the design and connection of the prevention and control methods of deep coal-rock gas dynamic disasters.

Modeling of olivine-spinel phase transformation of germanate olivine (Mg2GeO4) by using the phase-field method

Olivine is the main constituent of the upper mantle, and its phase transformation affects the rheology of the subduction zone. It is crucial to reveal the kinetics of the olivine (α)-spinel (γ) phase transformation under differential stress. To investigate the effect of microstructural properties on phase transformations, such as grain boundary energy and plastic strain, we conducted a phase-field simulation using germanate olivine, an analog of silicate olivine. We conducted simulations under various confining pressures of 1–5 GPa, temperatures of 1000 and 1200 K, with and without plastic strain, and various grain boundary energies. The volume fraction of spinel decreases as the overpressure (confining pressure) increases because the effect of the elastic strain energy owing to the large overpressure on spinel growth is larger than those of the interface mobility and chemical free energy. The spinel growth has two types: “spinel needle” parallel to the maximum compression direction and “spinel platelet” perpendicular to the maximum compression direction. The spinel needles constantly grow owing to the interface mobility controlled by the grain boundary diffusivity, whereas the spinel platelets grow while the plastic strain caused by the phase transformation and deformation decreases the elastic strain energy. The spinel growth produces further plastic strain; thus, the spinel growth progresses by this positive feedback between the transformation and deformation.

Dynamic Tensile Mechanical Properties of Outburst Coal Considering Bedding Effect and Evolution Characteristics of Strain Energy Density

The evolution of strain energy density of outburst-prone coal is of great significance for analyzing the characteristics of energy accumulation and release in coal and rock masses. The dynamic mechanical properties of coal samples were tested by using the split Hopkinson pressure bar (SHPB) technique. Dynamic tensile mechanical properties, layered effect and density evolution characteristics of strain energy for coal were studied. The dynamic failure and crack propagation process of the specimen were recorded with a high-speed camera. In addition, a digital image correlation (DIC) method was used to analyze the evolution characteristics of the strain field during the deformation process of the specimen. The distribution characteristics of the particle fragments were statistically analyzed. The results show that the bedding orientation of the coal has a significant effect on its deformation and damage features. The presence of weak planes, microcracks and laminae causes its shear damage zone to behave more complex. If the crack plane coincides with the high shear stress plane, the developed shear cracks extend along the weak laminae and the shear damage zones in BD specimens are not symmetrically distributed. When the laminated surface of the coal sample is at a certain angle with the impact loading direction, the damage mode is coupled with tensile and shear damage. The percentage mass distribution of particles and fines increases with increasing bedding orientation. The effect of water on the dynamic damage of coal samples is significant. Based on the principle of pressure expansion of wing-shaped cracks, the formula for calculating the dynamic strength of water-saturated coal samples under dynamic loading was derived.

Work softening mechanism and microstructure evolution of nanostructured Mg-8Gd-3Y alloy during severe shot peening

A two-step severe shot peening (SSP) method was designed to investigate the softening mechanism of nanostructured Mg-8Gd-3Y (GW83) alloys and its effects on the surface characteristics of the deformation layer. The experimental results indicated that a gradient deformation layer with nanocrystalline (50–100 nm) near the surface layer was fabricated by single SSP (0.54 mmN). The corresponding formation mechanism of nanocrystalline was mainly owing to continuous dynamic recrystallization (cDRX). By applying the two-step SSP (0.54 + 0.23 mmN) treatment, softening occurred near the surface layer (<50 μm) due to the occurrence of partial discontinuous dynamic recrystallization (dDRX). The reason for dDRX behavior during SSP treatment resulted from the combined effects of high-level stored strain energy and heat production. This softening behavior was characterized by the increase of domain size, the slight enhancement of basal texture, and the decrease of dislocation density and microhardness. Therefore, appropriate SP parameters should be selected to avoid material softening when obtaining nanocrystalline Mg alloys.

Stability of phase boundary between L12-Ni3Al phases: A phase field study

The evolution and stability of phase boundaries (PBs) between L12-Ni3Al phases in Ni75Al11V14 alloy aged at 1050k was studied using the microscopic equation phase-field method (MPFM). Four types of L12 PBs were found through atomic configuration, migration and occupation probability (OP). The evolution of metastable PBs and formation of stable PBs were tracked and explored, the effect of coherent elastic strain energy on the evolution and stability of PBs is also investigated by coupling the micro elastic theory with MPFM. In addition, the formation enthalpy, interface energy and electron distribution function of PBs are calculated by FP method, and the stability of PBs is further quantitatively predicted from the perspective of thermodynamic energy and gaining or losing electrons. FP calculation results are consistent with MPFM prediction, and the essence of the transition and stability of PBs is revealed based on the atomic migration dynamics, interface evolution morphology and thermodynamic energy. This is an effective method to further explore the formation and structure of PBs and design high stability PBs.

Effect of the mechanical properties of the cell membrane on the transition energy barrier of electroporation

The mechanical properties of the cell membrane play an important role in electroporation. This paper studied the influence of the mechanical properties of the cell membrane on the transition energy of electroporation through both modeling and experiments. An electromechanical coupling model of a single pore on the cell membrane was established in COMSOL, and the effect of elastic strain energy on the formation of pores was analyzed. Additionally, to compare the transition energy barrier of pores for different elastic properties of the cell membrane, electroporation experiments were carried out at different temperatures. The simulation showed that the elastic strain energy of the cell membrane increased the transition energy barrier of the pores. The experiments also showed that the transition energy barrier was larger when the elasticity of the cell membrane is intact, which was in good agreement quantitatively with the simulation results. We demonstrated that the mechanical properties of the cell membrane hinder the pore formation, which may be due to the increase of the transition energy barrier. We analyzed the possible mechanism of the effect of cell membrane mechanical properties on electroporation and found the contribution of cell membrane mechanical properties to electroporation during the delivery of exogenous substances, which can provide guidance for improving therapies in electrochemotherapy.

Multiaxial fatigue life assessment of 304 austenitic stainless steel with a novel energy-based criterion

A novel energy-based multiaxial fatigue criterion was proposed considering the effect of normal strain energy and shear strain energy. The difference of contributions of both the normal strain energy and shear strain energy on the failure of materials was identified by introducing the stress-path-dependent energy weight coefficient. A newly defined non-proportionality based on the stable hysteresis loops was introduced to the criterion considering the non-proportionality additional hardening behavior. Most of the coefficients can be determined by the monotonic tensile test which gives more opportunities for the applicability and feasibility of the new criterion in engineering practice. The performance of the new criterion was approved by comparing the predicted and tested life of SS304 under various multiaxial loading paths.

Effect of strain energy on corrosion behavior of ultrafine grained copper prepared by severe plastic deformation

Effect of strain energy on corrosion behavior of ultrafine-grained (UFG) copper prepared by severe plastic deformation (SPD) was investigated in terms of microstructural evolution. The SPD processed material showed an ultrafine-grained (UFG) structure after grain refinement for several time processes, which will affect mechanical and corrosion behavior Homogeneity can be obtained efficiently through the pressing process commonly known as simple shear extrusion (SSE), which is one of the SPD techniques. Pure copper was processed by SSE for two, four, eight, and twelve passes. The structure of SSE treated sample was observed by laser microscope and transmission electron microscope as well as X-ray diffraction. The corrosion behavior by potentiodynamic polarization curve was observed in modified Livingstone solution, 1 M NaCl, and sulphuric solution. The structure of SSE processed sample showed that the first pass of the SSE processed sample displayed large deformation by developing the elongated grain and sub-grain structure. By increasing the SSE pass number, the grain shape became equiaxed due to excessive strain. The X-ray broadening related to ultrafine-grained (UFG) structure processed SSE on the copper sample, leading to smaller crystallite size, higher microstrain, and higher dislocation density. More homogeneous passive film was developed on the material with UFG structure appearance. However, the current density in 1 M NaCl was decreased by an increment of pass number due to the dissolution of copper metal. The UFG structure has more boundaries than coarse grain structure, and these phenomena show why Cu dissolve ability influences the current density. The grain boundary behaves as the cathodic site.

Ferroelectric and Ferroelastic Domain Related Formation and Influential Mechanisms of Vapor Deposited Piezoelectric Thin Films

Compared to the bulk piezoelectric materials counterpart, piezoelectric thin films (PTFs) possess advantages of smaller size, lower power consumption, better sensitivity, and have broad application in advanced micro-electro-mechanical system (MEMS) devices. However, the performance of MEMS transducers and actuators are largely limited by PTFs piezoelectric properties. In this review, we focus on understanding structure-property relationship of vapor deposited PTFs, with emphasis on the effect of strain energy and electrostatic energy in thin films, especially, energy relaxation induced misfit dislocation and ferroelectric (FS) and ferroelastic (FC) domain formation mechanisms. We then discuss the microstructure of these domains and their influential mechanisms on piezoelectric properties, as well as the domain engineering strategies (i.e., internal and external stimuli). This review will motivate further experimental, theoretical, and simulation studies on FS and FC domain engineering in PTFs.

The Multiaxial Creep–Fatigue Failure Mechanism of Mod. 9Cr-1Mo Steel Under Non-proportional Loading: Effect of Strain Energy on Failure Lives

The Multiaxial Creep–Fatigue Failure Mechanism of Mod. 9Cr-1Mo Steel Under Non-proportional Loading: Effect of Strain Energy on Failure Lives

Hydride corrosion kinetics on metallic surface: a multiphase-field modeling

The hydride growth on metallic surface can cause material failure, which is a significant form of pitting corrosion. A new multiphase-field model is constructed to study the hydride corrosion kinetics, in which three order parameters are introduced to represent the passive film, hydride and metal phase, respectively. Coupling with hydrogen concentration field and elastic strain field, this model not only presents the growth of hydride and the rupture of passive film, but also reveals the hydrogen diffusion mechanism and the effect of strain energy on pitting corrosion process. The simulation shows the semi-ellipsoidal cerium hydride forms and grows near the passive film/cerium interface. During this process, the passive film on the upper side of the hydride is also hydrogenated or peeled off, resulting in faster hydrogen transport, which in turn promotes the growth of hydride. The formation of cerium hydride causes volume expansion, and the strain energy is mainly distributed around the hydride, which inhibits its growth. The present study contributes to understanding the formation mechanism of hydride corrosion at mesoscale, especially the pitting corrosion kinetics of rare earth metals.

Effect of dilatational strain energy of Fe-C-Ni system on martensitic transformation

Effect of dilatational strain energy of Fe-C-Ni system on martensitic transformation

Extraordinary warm ductility of a Mn-rich high-strength steel achieved at temperature below 0.5 Tm

Abstract This work employed austenite reversion during deformation to achieve large ductility at a temperature below 0.5 Tm (melting temperature) in Mn-rich high strength steels. This goal was achieved in a Mn-rich steel without Al, in which a higher austenite reversion rate below 0.5 Tm was obtained. The tensile results evidenced the extraordinary ductility of over 90% at 550 °C, which is about 0.48 Tm of the steel. Thermodynamic calculation was applied to elucidate the effects of Al and strain energy. Moreover, electron backscatter diffraction was used to investigate microstructure evolution under various conditions. It was found that rate of austenite reversion is more critical than ferrite recrystallization in enhancing ductility during warm deformation.

Modeling of In0.17Ga0.83N/InxGa1–xN/AlyGa1–yN light emitting diode structure on ScAlMgO4 (0001) substrate for high intensity red emission

An In0.17Ga0.83N light emitting diode (LED) structure on ScAlMgO4 (0001) substrate is modeled for high intensity red emission. The high indium composition (In &gt; 15%) inside the c-plane polar quantum well (QW) for longer wavelength emission degrades the structural and optical properties of LEDs because of induced strain energy and quantum confinement Stark effect. To compensate these effects, it has been demonstrated by simulation that an AlyGa1–yN cap layer of 2 nm thick and Al composition of 17% deposited onto QW of 3 nm thick and In composition of 35% will allow to have less defect density and higher intensity red emission at 663 nm than that of In0.17Ga0.83N/InxGa1–xN LEDs grown on ScAlMgO4 (0001) substrate. This LED structure has perfect in-plane equilibrium lattice parameter (αeq = 3.249 Å) and higher logarithmic oscillator strength (Γ = –0.93) values.

Effect of local strain energy to predict accurate phase diagram of III–V pseudobinary systems: case of Ga(As,Sb) and (In,Ga)As

This work proposes an efficient and accurate methodology of ab initio thermodynamics to predict phase diagrams of III–V pseudobinary systems. The innumerable configurations of solid solutions are efficiently considered while maintaining accuracy by calculating the energies of freely relaxed configurations with the combined methodology using density functional theory calculations and cluster expansion. Then, the thermodynamic properties are calculated following a grand canonical ensemble framework that takes into account the local compositional fluctuation. The local strain energy induced by this local compositional fluctuation is found to be independent of the configuration; hence, it is calculated separately and added to the energy of a freely relaxed configuration, which significantly reduces the computational cost. This novel methodology is applied to calculate the phase diagrams of Ga(As,Sb) and (In,Ga)As, showing a good agreement with previous experimental reports. Notably, the strain energy is indispensable to predict phase diagrams accurately. It implies both the validity and the applicability of this method to other III–V pseudobinary systems. From an understanding of the crucial role of the strain energy in phase separation, an intuitive prediction is suggested through a simple estimation of the strain energy using the ratio of lattice parameters between various III–V semiconductor materials.

Effect of strain energy on the grain growth behaviour of ultrafine-grained iron-chromium alloy by equal channel angular pressing

The grain growth of an ultrafine-grained iron-chromium alloy has been investigated focusing on the early stage of restoration of strain. Ultrafine-grained (UFG) material has been prepared by equal channel angular pressing (ECAP) up to eight passes via route Bc. The post-ECAP annealing process was completed from 473 until 1373 K for one hour. The microstructure and hardness were then analyzed by electron back-scattering diffraction, transmission electron microscope, X-ray diffractometer and microhardness. The hardness after post-ECAP annealing exhibited the typical three-stages softening. Namely, the hardness remained stable after the annealing temperature up to 698 K and then declined significantly until the temperature of 973 K. Finally, hardness remained stable again at a higher temperature. In the second stage, grains grew uniformly, which differ from the typical nucleation-and-growth mode of discontinuous recrystallization. It was found by X-ray line broadening analysis that strain was released in the early stage prior to the significant softening stage. It was suggested that the homogeneous grain growth was led by the uniform grain distribution with a high angle grain boundaries fraction.