Stress Hysteresis Research Articles

Thermal activation of stress-induced martensitic transformation in Ni-rich Ti-Ni alloys

We performed compression tests at low temperatures under various strain rates for Ni-rich Ti-Ni alloys. Thermal activation theory for the habit plane motion with a thermal activation energy of ~0.5 eV successfully reproduced both the examined temperature and strain-rate dependences of the transformation stress hysteresis. This indicates that the thermal activation process of the habit plane motion underlies the dramatic increase in the transformation hysteresis at lower temperatures in this system. These findings are critical to elucidate the physical impact of the thermal activation nature on the transformation hysteresis and to consider the feasibility of low-temperature operation of shape-memory functions.

Hoop Stress Modification, Stress Hysteresis and Degradation of a REBCO Coil Due to the Screening Current Under External Magnetic Field Cycling

Degradation of a REBCO coil under external magnetic fields is one of the major technical problems in the field of HTS magnet technology. A possible cause of such degradation is an inhomogeneous hoop stress distribution, or hoop stress modification (both increase and decrease), induced by the screening current. In this work, we investigate such a hoop stress modification by a small coil experiment with a strain measurement and a numerical simulation. An experimental result shows a very high stress increase factor of >4.1, defined by the maximum circumferential stress over BzJR stress, and the simulated result is in qualitative agreements. The strain (stress) shows a hysteresis effect corresponding to the screening current behavior. A large hoop stress modification causes not only a hoop stress increase, but also buckling of the conductor, which induces delamination and micro-clacks of the superconducting layer. We also show the stress modification can be reduced by bonding turns with epoxy.

Large tunable elastocaloric effect in additively manufactured Ni–Ti shape memory alloys

High-efficiency elastocaloric refrigeration requires high-performance elastocaloric materials with both large surface areas to promote heat exchange rate and large elastocaloric effects to increase the amount of heat transfer. Ni–Ti shape memory alloys (SMAs) are the most promising elastocaloric materials but they are difficult to process by conventional methods due to their poor manufacturability. Here, we successfully developed Ni–Ti SMAs with large elastocaloric effects by additive manufacturing which has the capability to fabricate complex geometries with large surface areas. The phase transformation temperatures of these additively manufactured Ni–Ti SMAs, fabricated by selective laser melting (SLM), can be tuned by varying the SLM processing parameters and/or post heat treatments and thus tunable large elastocaloric effects were achieved at different temperatures, which can be used for different applications. Owing to its large transformation entropy change and high yield strength as a result of precipitation hardening, the aged SLM fabricated alloy exhibits a remarkably large elastocaloric effect with an adiabatic temperature change as high as 23.2 K, which is among the highest values reported for all Ni–Ti SMAs fabricated by both conventional methods and additive manufacturing. Furthermore, by virtue of the high yield strength and low stress hysteresis of the aged alloy, this large elastocaloric effect shows good stability during cycling. The achievement of such large elastocaloric effects in alloys fabricated by near-net-shape additive manufacturing may accelerate the implementation of high-efficiency elastocaloric refrigeration. This study is instructive for the development of advanced high-performance solid-state refrigeration materials by additive manufacturing.

Low-temperature superelasticity and elastocaloric effect in textured Ni–Mn–Ga–Cu shape memory alloys

The superelastic behavior and elastocaloric effect of a [001]-textured Ni50Mn23Ga25Cu2 polycrystal have been investigated below room temperature (256–294 K). The adiabatic temperature change caused by rapid unloading of uniaxial stress reached −4.3 K at 259 K. A small stress hysteresis of 14 MPa was observed. Due to the low hysteresis energy loss (0.37 MJ m−3) stemming from the texture structure, the coefficient of performance (COPmat) of our alloy was calculated to be 18, indicating that it is a promising elastocaloric candidate for low-temperature refrigeration.

Effects of morphology of V nanowires on superelasticity of Ti46Ni44V10 alloy

The present study investigated the effects of morphology of V nanowires on superelasticity of Ti46Ni44V10 alloy. The microstructure analysis revealed that the diameter of V nanowires decreased and the continuity improved with an increase in cold drawn deformation. The upper plateau stress decreased with the increase in annealing temperature and increased with the increase in cold working. Furthermore, the superelastic strain decreased with the increase in annealing temperature. However, it was independent of cold working. The stress hysteresis increased with the increase in area reduction, and the samples annealed at 400 °C exhibited a larger hysteresis than those annealed at 350 °C when the area reduction was more than 40%. Thus, we found that, the effects on superelasticity of Ti46Ni44V10 alloy were closely related to the morphology of V nanowires and the NiTi phase.

Polyurethane composite foams including CaCO3 fillers for enhanced sound absorption and compression properties

Polyurethane (PU) foams are versatile in automotive applications for sound absorption and seat cushioning products due to their easiness of manufacturing process and cost effectiveness. In this study, PU composite foams including CaCO3 fillers after chemical treatments with oleic acid were fabricated to examine the sound absorption and compressive properties. The cell and pore sizes in the PU composite foams did not show much differences with filler contents, but the open porosity revealed clear difference depending on the chemical treatments. The open porosity had lower values with chemically treated fillers than with no-treated cases, and it resulted in the high sound absorption coefficient. The compression strengths were also higher with the chemically treated fillers than with no-treated filler cases. Stress relaxation and hysteresis loss showed superior results with the chemically treated fillers compared with the cases with no-treated cases, and it is mainly due to the enhanced interfacial contacts and compatibility between PU matrix and CaCO3 filler surfaces. Therefore, it is much important to modify the filler surface characteristics for good interfacial compatibility to achieve improved physical properties of the PU composite foams.

A New Viscous Potential Function for Developing the Viscohyperelastic Constitutive Model for Bovine Liver Tissue: Continuum Formulation and Finite Element Implementation

The mechanical behavior of very soft tissues, such as liver, brain, kidney, etc. is assumed to be viscohyperelastic. The conventional approaches like quasi-linear viscoelastic (QLV) are limited to low strain rates and are unable to capture the short-term memory effects. In this paper, a new viscohyperelastic constitutive model is presented in which the strain energy function is decomposed into an elastic and a viscous part. The elastic part of the strain energy is assumed as a Mooney–Rivlin model, while a new viscous potential, as a function of strain and its rate, is proposed. Unconfined uniaxial compression tests are conducted up to 10% compression at two loading velocities of 1.3 and 10.56[Formula: see text](mm/min), to determine the material constants. A numerical simulation is also used to investigate the model-predicted material behavior. It is shown that the model is more sensitive to the hyperelastic parameters than the viscous parameters. This model is also able to predict the stress relaxation and hysteresis; however, an instantaneous relaxation is observed.

Large elastocaloric effect in directionally solidified all-d-metal Heusler metamagnetic shape memory alloys

Solid-state cooling based on the caloric effect of phase transformation materials has attracted considerable interest with the increased demand for energy-efficient and environmentally friendly cooling technologies. Here, we have systematically studied the microstructural evolution, martensitic transformation (MT) behaviors, and elastocaloric effect (eCE) of directionally solidified Ni35.5Co14.5Mn35Ti15 all-d-metal Heusler metamagnetic shape memory alloys. Electron backscatter diffraction (EBSD) analysis revealed the coexistence of Heusler-type 〈001〉-oriented dendritic crystal and Ti-poor interdendritic phase for as-solidified alloys. Upon homogenization annealing, the sample presents a columnar-like morphology with 〈105〉 textured five-layer-modulated (5 M) martensite along the growth direction. Besides, the multi-modulated martensite with 7 M and 8 M structures was identified by transmission electron microscopy (TEM). Using a unique technique of in situ digital image correlation (DIC) with the combination of infrared thermography, MT and eCE behaviors were studied. Ni35.5Co14.5Mn35Ti15 alloy yielded a large adiabatic temperature change (ΔTad) of 11.5 K with a low critical stress (σcr) of 38 MPa and a moderate stress hysteresis (Δσhy) of 54 MPa when subjected to uniaxial stress, resulting in the largest value of |ΔTad/σcr| = 0.31 K MPa−1. This improved eCE is attributed to the enhanced compatibility in the oriented polycrystalline alloy and the high mobility of the low-energy twin boundary in the multi-modulated martensite.

The association between oxidative stress and corneal hysteresis in patients with glaucoma

Systemic antioxidative status has been implicated in glaucoma pathogenesis. Additionally, corneal hysteresis (CH) may contribute to glaucoma progression. Here, we evaluated the relationship between biological antioxidant potential (BAP) and CH. This study included 103 patients with open-angle glaucoma (OAG). We used a free radical analyzer to measure BAP, and an ocular response analyzer to measure CH and corneal resistance factor (CRF). We evaluated the relationship between systemic oxidative stress and other clinical parameters with Spearman’s rank correlation test and a multi-regression analysis. BAP was not correlated to either CH or CRF in the male or female OAG patients. BAP was correlated to both CH and CRF in the female OAG patients older than 57 years (r = 0.51, P = 0.003; r = 0.49, P = 0.004), but uncorrelated in the female OAG patients younger than 57 years. Multiple regression analysis revealed that BAP independently contributed to CH (P = 0.025) and CRF (P = 0.015) in the older female OAG patients. Systemic oxidative stress may significantly affect the viscoelasticity of the cornea in older female OAG patients. Future studies are needed to confirm that low systemic antioxidative status and low corneal hysteresis contribute to glaucoma pathogenesis.

Orientation Dependence of Superelasticity and Stress Hysteresis in Cu–Al–Mn Alloy

Orientation Dependence of Superelasticity and Stress Hysteresis in Cu–Al–Mn Alloy

Investigation on the micro-mechanism of martensitic transformation in nano-polycrystalline NiTi shape memory alloys using molecular dynamics simulations

In this study, the temperature- and stress-induced martensitic transformations in nano-polycrystalline nickel-titanium shape memory alloys were investigated using molecular dynamics simulations, and in turn the micro-mechanism was examined at the atomic scale. The transformation temperature and the stress hysteresis were found to decrease with the decreasing grain size when the grain size was less than 50 nm. The observed martensite variants’ nucleation and growth phenomena during the martensitic transformation and its reverse one clearly demonstrated that the martensitic transformation was attributed to the formation of compound nanotwins structure inside the nano grains, which was a reasonable agreement with available experimental data.

Martensitic transformation and elastocaloric effect of Ti–Ni–Cu–Al microwire

Phase transformation behavior and elastocaloric effect have been studied in a microwire (~200 µm in diameter) of a Ti-44Ni-5Cu-1Al (at%) alloy. The microwire was fabricated by cold drawing followed by annealing at 673 K for 10 min. The microwire exhibited large superelastic strain of ~5% with a small stress hysteresis of ~80 MPa at room temperature when a stress of 400 MPa was applied. The microwire also exhibited a large elastocaloric effect; the adiabatic temperature decrease caused by stress removal from 400 MPa reached 14 K, which is consistent with the value expected from the Maxwell relation. No remarkable deterioration in superelasticity and elastocaloric effect was observed up to 600 stress cycles. Nanoscale microstructure with grain width of ~40 nm is probably the main reason for the excellent fatigue resistance.

Material‐related losses of natural rubber composites with surface‐modified nanodiamonds

ABSTRACTDielectric elastomer generators (DEGs) offer a solution for the growing sustainable energy needs. Despite the active research on DEGs, currently used materials do not possess the required properties to achieve the full potential performance of such generators, thus, limiting an economical attractiveness of DEGs. Therefore, tailor‐made materials for DEGs are in demand. Customizing the natural rubber recipe allows both dielectric and mechanical loss reduction, while the addition of nanodiamonds lowers the stress relaxation and hysteresis loss even further. The effect is most pronounced after chemical modification of nanodiamonds with silane coupling agents. Moreover, such modified nanodiamonds show less dielectric losses compared to unmodified nanodiamonds and allow reducing the dynamic loss tangent of the compound. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48629.

The orientation dependence of thermal and stress hysteresis at R–B19’ martensitic transformation in aged Ni50·6Ti49.4 single crystals

The influence of the orientation on thermal and stress hysteresis at the R–B19’ martensitic transformation in aged [001]- and [112]-oriented Ni50·6Ti49.4 single crystals with small particles, was studied. At low stresses (<100 MPa) in the [001]-orientation the thermal hysteresis of stress-induced R–B19’ martensitic transformation is larger than in [112]-orientation. This is associated with the different structure of R-martensite under stress: multivariate structure in [001]-orientation and oriented R-martensite in [112]-orientation. At high stress (>300 MPa) during B2–B19’ martensitic transformation the hysteresis in [001]-orientation is lower than in [112]-orientation. In the high-strength [001]-orientation, the strong dependencies of thermal hysteresis on stress and of stress hysteresis on temperature (hysteresis reduce in 2.5–3.4 times), were found during the R–B19’ martensitic transformation. The main factors determining this dependence were: a formation of B19′-martensite from the multivariate structure of the R-phase, a high-strength yield level of the B2-phase, an absence of detwinning of B19′-martensite and a change in the lattice parameters of the R-phase with increases in temperature and stress. In the low-strength [112]-orientation, the strength properties of the B2-phase are three times lower than in the [001]-orientation, the stress-induced B19′-martensite is formed from the oriented R-martensite, and the B19′-martensite cannot be detwinned under stress. These factors cause a slight dependence of the thermal hysteresis on stress.

Low‐cycle fatigue of IN 718: Effect of waveform

AbstractThe influence of various strain waveforms on the low‐cycle fatigue of IN 718 tested at 650°C has been investigated. The straining paths are accompanied by dwell‐induced creep component(s) or unequal strain distribution in different portions of cycles reducing strength of material. The investigation intends to clarify mainly mechanistic aspects of relaxation‐fatigue interaction. Features of time‐dependent effect induced by nonpeak dwell and the same accompanied by peak dwell, slow unloading from the peak to a lower strain, and different loading and unloading rates are compared in terms of stress amplitude responses, mean stress relaxation, hysteresis loops, life, and damage parameter DC‐F. Softening is common in all the cases, and degree of softening varies linearly with life. The energy‐based life prediction model has been found to work well for the data, and we have introduced energy fraction–based approach to observe simultaneous contribution from both creep and fatigue on life.

Simulation of Stress Hysteresis Effect on Permeability Increase Risk Along A Fault

CO2 sequestration projects will in the coming years include both aquifer and depleted oil and gas field sites, with different stress paths and history. Stress changes and stress concentration effects on faults will have to be readily assessed, potentially endangering shallower permeable formations. Usually, a fault is modeled as a singularity with shear strength or friction properties, and simulations are run to determine whether the fault is reactivated through shear failure. In this paper, we model a simple rectilinear fault as a finite surface with lowered mechanical properties compared to elsewhere in the domain, which represents a fractured zone alongside the fault core. SINTEF’s Modified Discrete Element code is used coupled to the flow simulator TOUGH2, to model the fracture initiation and propagation, monitoring the permeability increase along the fault. A simplified scenario is simulated, with a sandstone storage reservoir bounded by a fault, penetrating a shale caprock to a shallower sandstone layer. The storage site either undergoes depletion before CO2 injection or has its pore pressure increased to simulate the case of aquifer storage. Results show that during depletion, shear stresses may develop such that fractures propagate alongside the fault to the upper aquifer. However, for the mirror fault orientation with regards to verticality, no such fractures develop. These results are reversed for the aquifer storage case.

The effects of nanoclay and deformation conditions on the inelastic behavior of thermoplastic polyurethane foams

Abstract Under cyclical loading–unloading compression conditions, flexible thermoplastic polyurethane (TPU)/nanoclay composite foams exhibit inelastic behaviors consisting of stress softening, hysteresis loss, and residual strain. In this research, the inelastic behavior of TPU and TPU/nanoclay composite foams was investigated by incorporating different amounts of nanoclay and maximizing strain deformation conditions. As the maximum compression strain was increased from 20% to 40%–60%, the inelastic behavior of TPU neat resin foams (TPUNR) with the same microcellular structures became more profound. Transmission electron microscopy (TEM) and compression testing results indicated that the nanoclay fillers were dispersed in the cell walls (struts). Fully exfoliated nanoclay increased the material's compression strength from 0.13 MPa for TPUNR foam to 0.16 MPa for TPU/5 wt% nanoclay foam (TPUNC5) and 0.36 MPa for TPU/10 wt% nanoclay foam (TPUNC10). With increasing nanoclay content, the relative hysteresis loss, relative residual strain, and relative stress softening of the TPU/nanoclay composite foams decreased markedly. Cell deformation mechanism analyses revealed that the dispersed nanoclay in the cell walls effectively reinforced the foams and retarded the permanent deformation of the cell walls, thereby reducing the inelastic behavior of the TPU/nanoclay foams. That is, the addition of organically modified nanoclay provided an effective way to tune the inelastic behavior of TPU and TPU/nanoclay composite foams.

Experimental study on panel zone behavior of diaphragm-through connections to concrete-filled tube columns

In order to verify the accuracy of the panel zone shear capacity calculation method of diaphragm-through connections which were proposed in previous research, the low cycle repeated load tests of six cross-shaped specimens were carried out. The seismic performance of the panel zone’s stress distribution, failure mode, hysteresis curve, and skeleton curve are comprehensively studied and analyzed. The results showed that the steel tube web and core concrete were mainly participating to bear the horizontal shear force, and the “steel frame” composed of the steel tube flange and through-diaphragm was negligible for the shear resistance; the core concrete strut calculated width and height were all one-fourth of the height and width of the panel zone. The test results are in good agreement with the results of the calculation method, which indicated that the calculation method proposed in the previous research results had good accuracy and applicability, and would use for the panel zone shear capacity calculated in the connections design.

Axial Compressive Performance of CFRP Confined Self-stressing High-strength Concrete Cylinders

Due to the advantages of FRP (fiber reinforced polymer), such as light weight, high strength and corrosion resistance, FRP-confined concrete columns are gradually applied in civil engineering structures and have drawn wide attention from the engineering community. In order to avoid the stress hysteresis of CFRP (carbon fiber reinforced polymer) and make full use of FRP materials, expansive agent was added to concrete to make self-stressing high-strength concrete. In this study, the axial compression performance of 18 CFRP-confined self-stressing high-strength concrete cylinders was examined. The parameters include the CFRP layers and the level of prestress (with or without prestress). Experimental results show that 3.53–5.34 MPa prestress in concrete and 799.3–1584.2 MPa prestress in CFRP are produced in the composite cylinder. The stress-strain curves obtained from the experiment shows that the intercept stress, inflection stress and peak stress of the self-stressing specimens are all higher than those of the non-prestressed specimens. With the application of prestress, the utilization ratio of CFRP increases as well. In the theoretical calculation of intercept and peak stress, by modifying the existing models, the experimental results are in good agreement with the calculated results.

On stress-induced voltage hysteresis in lithium ion batteries: Impacts of surface effects and interparticle compression

Application of silicon in high capacity electrodes of lithium ion battery suffers from stress effects and, in turn, affects voltage performance of battery. This paper established a reaction-diffusion-stress coupled model and investigated the stress induced voltage hysteresis with consideration of diffusion induced stress, surface effects and interparticle compression. It was found stress and stress induced voltage hysteresis depended on particle size. In big particles, diffusion induced stress is dominant and leads to significant hysteresis in both stress and voltage, indicating energy dissipation due to stress effects. In small particles, e.g., radius of dozens nanometers, diffusion induced stress was negligible while surface effects played dominant role, leading to nearly vanished voltage hysteresis shifting away from equilibrium potential. According to calculation, particle sizes around 100 nm are appropriate choice for electrode design as both diffusion induced stress and surface effects are insignificant. Finally, interparticle compression pushed the stress hysteresis to compressive side and led to early termination of lithiation at cut-off voltage. Denser electrode would enhance this effect. It indicated that there must be a limit of mixing ratio of silicon because higher interparticle compressive stress due to more introduced silicon would impede the battery from fully charged.