Increasing Strain Ratio Research Articles

Study the Influence of X-ray on the Optical and Mechanical Properties of CMC HV/ PAC LV Polymeric Films

IIn this work, carboxymethyl cellulose/polyanionic cellulose (CMC HV/PAC LV) films were prepared and exposed to different X-ray doses (0, 200, 400, 600 and 800 cGy). Absorption and transmission measurements of the ultraviolet spectrum of the incident light were studied with a DU 800 spectrophotometer. Stress and strain were calculated by applying a tensile force to the samples and increasing its amplitude until the sample breaks. Applying this force to the samples increased the length of the samples. The absorption of CMC HV/PAC LV films increased with increasing X-ray dose, and therefore, the absorption coefficient increased with increasing X-ray dose. The results show that the amount of spectral transmittance of the films decreased with increasing X-ray dose, indicating that the opacity of the samples increased with increasing X-ray dose. The characteristic absorption peaks are observed at 275 nm-1, 328 nm-1, 345 nm-1, 370 nm-1, and 470 nm-1, indicating molecular bonding. Increasing the X-ray dose decreases the elastic modulus of the films, and the stress amplification factor decreases with increasing strain ratio, indicating that X-ray photon irradiation leads to a decrease in the elasticity of the films. The results of this research may be useful in many fields, including industrial, medical or scientific research, as well as in oil fields.

Effect of strain ratio and pre-strain on the low-cycle fatigue behavior of 4130X steel at different strain amplitudes

This study investigates the impacts of strain ratio and pre-strain on the low-cycle fatigue properties and microscopic damage mechanisms of 4130X steel across varying strain amplitudes. Under symmetric loading, initial cycles at low strain amplitudes demonstrate clear peak/valley stress hardening followed by cyclic softening in later stages of fatigue. In contrast, the hardening behavior vanishes at higher strain amplitudes. Increasing strain ratio and pre-strain cause the initial hardening behavior at low strain amplitudes to gradually disappear. Additionally, at lower strain amplitudes, fatigue life decreases as strain ratio and pre-strain rise, attributed to substantial tensile mean stress. Microscopic examination reveals that symmetric cyclic loading at low strain amplitudes releases stress concentrations caused by quenched and tempered processing and reduces both dislocation density and localized plastic strain. Conversely, at higher strain ratios and pre-strains, increased tensile mean stresses not only intensify dislocation multiplication, resulting in high dislocation density, but also activate multi-slip system, leading to dislocation cross-slip. Moreover, at a high strain amplitude of 0.45 %, pre-strain aids in martensite recovery and promotes dislocation annihilation during recovery, thus inducing cyclic softening. Finally, the fatigue lives under varied loading conditions are compared with the fatigue design curve prescribed by ASME VIII-II code.

Prediction of disease-free survival using strain elastography and diffuse optical tomography in patients with T1 breast cancer: a 10-year follow-up study

BackgroundEarly-stage breast cancer (BC) presents a certain risk of recurrence, leading to variable prognoses and complicating individualized management. Yet, preoperative noninvasive tools for accurate prediction of disease-free survival (DFS) are lacking. This study assessed the potential of strain elastography (SE) and diffuse optical tomography (DOT) for non-invasive preoperative prediction of recurrence in T1 BC and developed a prediction model for estimating the probability of DFS.MethodsA total of 565 eligible patients with T1 invasive BC were enrolled prospectively and followed to investigate the recurrence. The associations between imaging features and DFS were evaluated and a best-prediction model for DFS was developed and validated.ResultsDuring the median follow-up period of 10.8 years, 77 patients (13.6%) developed recurrences. The fully adjusted Cox proportional hazards model showed a significant trend between an increasing strain ratio (SR) (P < 0.001 for trend) and the total hemoglobin concentration (TTHC) (P = 0.001 for trend) and DFS. In the subgroup analysis, an intensified association between SR and DFS was observed among women who were progesterone receptor (PR)-positive, lower Ki-67 expression, HER2 negative, and without adjuvant chemotherapy and without Herceptin treatment (all P < 0.05 for interaction). Significant interactions between TTHC status and the lymphovascular invasion, estrogen receptor (ER) status, PR status, HER2 status, and Herceptin treatment were found for DFS(P < 0.05).The imaging–clinical combined model (TTHC + SR + clinicopathological variables) proved to be the best prediction model (AUC = 0.829, 95% CI = 0.786–0.872) and was identified as a potential risk stratification tool to discriminate the risk probability of recurrence.ConclusionThe combined imaging-clinical model we developed outperformed traditional clinical prognostic indicators, providing a non-invasive, reliable tool for preoperative DFS risk stratification and personalized therapeutic strategies in T1 BC. These findings underscore the importance of integrating advanced imaging techniques into clinical practice and offer support for future research to validate and expand on these predictive methodologies.

Low-cycle fatigue behavior of Silafont®-36 automotive aluminum alloy: Effect of negative strain ratio

The aim of this study was to determine cyclic deformation behavior of a high-pressure die-cast Silafont®-36 automotive alloy with heterogeneous microstructures, focusing on the effect of strain ratio (Rε) ranging from negative infinity (-∞) to +0.5 at a constant strain amplitude of 0.4%. Pronounced cyclic hardening behavior was observed from the stress-strain hysteresis loops at different strain ratios. The degree of cyclic hardening, evaluated via both the traditional method and a newly-proposed slope method, increased with decreasing strain ratio. Fatigue life of the alloy was slightly lower at positive strain ratios, with its peak emerging at zero mean strain (or Rε = −1). In the negative range of strain ratios (Rε<−1), the fatigue life increased slightly with increasing strain ratio, which was mainly related to the plastic strain amplitude. A new power-law based equation was proposed to describe the change of mean stress relaxation at negative strain ratios (Rε<−1), along with a polynomial equation for depicting the situation at zero and positive strain ratios. Strain-energy density analyses corroborated that the intrinsic fatigue toughness was a material constant since it was not affected by strain ratio.

Development of a Formability Prediction Model for Aluminium Sandwich Panels with Polymer Core.

In the present work, the compatibility relationship on the failure criteria between aluminium and polymer was established, and a mechanics-based model for a three-layered sandwich panel was developed based on the M-K model to predict its Forming Limit Diagram (FLD). A case study for a sandwich panel consisting of face layers from AA5754 aluminium alloy and a core layer from polyvinylidene difluoride (PVDF) was subsequently conducted, suggesting that the loading path of aluminium was linear and independent of the punch radius, while the risk for failure of PVDF increased with a decreasing radius and an increasing strain ratio. Therefore, the developed formability model would be conducive to the safety evaluation on the plastic forming and critical failure of composite sandwich panels.

Biaxial test method for determination of FLCs and FFLCs for sheet metals: validation against standard Nakajima method

Recently, a biaxial test method comprising a cruciform specimen design and spatio-temporal method to determine the limit strains has been proposed for the determination of forming limit curves (FLCs) and fracture forming limit curves (FFLCs) for sheet metals. However, this test method has not yet been validated against the existing standard methods. In the present work, this biaxial test method has been applied to the aluminium alloy AA5754 for formability evaluation at room temperature and results from the biaxial test method have been compared with those from the standard Nakajima method. Theoretical analysis has been carried out to compare equi-biaxial tension cases for the two methods; a similar variation of thickness strain with radial distance normalised by the radius of the gauge area is found between the two methods. In the biaxial tests, decreasing the radius of the through-thickness dome profile, with which the gauge area is thinned, leads to fracture nearer the specimen centre but produces a less uniform strain distribution. Importantly, the major strains at necking on the FLC, as determined using the biaxial and the standard test methods, are almost the same in the plane-strain state, while in other strain states, the major strains are slightly lower for the biaxial method than that for the Nakajima method. An FFLC for AA5754 has also been determined using the biaxial test method, in which the major strain at fracture decreases with increasing strain ratio β from −0.5 to 0, while it changes only slightly when β > 0.

Effect of unequal biaxial tensile strains on the filtration behaviour of continuous filament needle-punched nonwoven geotextiles

The effect of unequal biaxial tensile strains on the filtration behaviour of continuous filament needle-punched nonwoven geotextiles was investigated via gradient ratio tests. The filtration behaviour of four groups of unequal biaxial tensile strains were examined, including the gradient ratio (GR), permeability of the soil-geotextile system, mass of soil loss, and permittivity of pure geotextiles. The strains in the machine direction of a geotextile in the four groups were the same, ranging from 10% to 30%, with the ratios of the strain in the machine direction to that in the cross-machine direction set to 1, 2, 3, and 4, respectively. It is shown that for the same strain ratio, the GR value at the time of test termination (GRt) increases with increasing strain, and the permeability of the soil-geotextile system, permittivity of pure geotextiles, and the soil loss decrease with increasing strain. For the same strain in the machine direction, there are general decreasing trends for the GRt value and soil loss with increasing strain ratio, and the permeability of the soil-geotextile system and permittivity of pure geotextiles under equal biaxial tensile strains are higher than those under unequal biaxial tensile strains.

Uniaxial Stretching of Cell-Laden Microfibers for Promoting C2C12 Myoblasts Alignment and Myofibers Formation.

Fiber-shaped cellular constructs have attracted increasing attention in the regeneration of blood vessels, nerve networks, and skeletal myofibers. Nevertheless, the generation of functional fiber-shaped cellular constructs suffers from limited appropriate microfiber-based fabrication approaches and the maintenance of regenerated tissue functions. Herein, we demonstrate a silicone-tube-based coagulant bath free method to fabricate tens of centimeters long cell-laden microfibers using single UV exposure without pretreatment of nozzles or microchannels. By modulating the exposure time, the gelatin methacrylate microfibers with tissue-like microstructures and mechanical properties are obtained. Then, a culture system integrated with a pillar well-array based stretching device is used to apply uniaxial stretching with various strain ratios in situ to cell-laden microfibers in a 60 mm petri dish. Cells with improved spreading, elongation, and alignment are obtained under uniaxial stretching. Moreover, the promotional effects of uniaxial stretching on the differentiation of C2C12 myoblasts, the formation, and contractility of myofibers become more pronounced with increasing strain ratio and achieve saturation level as strain ratio up to ∼35%.

Effect of novel supported vulcanizing agent on the interfacial interaction and strain-induced crystallization properties of natural rubber nanocomposites

The influence of the novel vulcanizing agent, silica supported sulfur monochloride (silica-s-S), comparing with sulfur on the filler-rubber interfacial interaction, mechanical properties and the strain-induced crystallization behaviors were investigated. Due to the formation of interparticle domain, silica-s-S immobilized more rubber chains approaching its surface as the crosslinking points than sulfur vulcanization system. Furthermore, the tightly immobilized rubber chains on silica-s-S surface bring to the significant enhancement of mechanical properties of NR nanocomposites. Meanwhile, the immobilized rubber chains also induced the formation of highest initial crystallinity index and slower decreasing lateral crystallite size with increasing strain ratio. Silica-s-S with more tightly immobilized rubber chains approaching its surface shown better reinforcing effect and strain-induced crystallization behaviors on rubber than that of sulfur vulcanization system.

Modulating thermal conduction by the axial strain

Recent studies have revealed that the symmetry of interparticle potential plays an important role in the one-dimensional thermal conduction problem. Here we demonstrate that, by introducing strain into the Fermi–Pasta–Ulam-β lattice, the interparticle potential can be converted from symmetric to asymmetric, which leads to a change of the asymptotic decaying behavior of the heat current autocorrelation function. More specifically, such a change in the symmetry of the potential induces a fast decaying stage, in which the heat current autocorrelation function decays faster than power-law manners or in a power-law manner but faster than ~t−1, in the transient stage. The duration of the fast decaying stage increases with increasing strain ratio and decreasing of the temperature. As a result, the thermal conductivity calculated following the Green–Kubo formula may show a truncation-time independent behavior, suggesting a system-size independent thermal conductivity.

Cyclic deformation and anelastic behavior of ZEK100 magnesium alloy: Effect of strain ratio

Wrought magnesium alloys with low rare-earth (RE) contents are being considered for lightweight automotive applications. The purpose of this study was to identify the effect of strain ratio on cyclic deformation behavior of a rolled ZEK100-O Mg alloy with 0.2wt% neodymium. The microstructure in its annealing condition consisted of equiaxed grains which were oriented with most c-axes perpendicular to the rolling direction. This alloy exhibited a superior combination of tensile strength and ductility due to its weak basal texture and decreased stacking fault energy. Significant plastic deformation occurred in the tensile phase of the first cycle at strain ratios of Rε=0 and 0.5. The asymmetry of initial hysteresis loops tended to diminish towards the mid-life cycles. With increasing strain ratio, fatigue life first increased, reached its maximum at a strain ratio of Rε=−1, and then decreased. This was attributed to a combined effect of mid-life stress amplitude, plastic strain amplitude and mean stress, where the stress amplitude increased and plastic strain amplitude decreased with increasing strain ratio. The closer the strain ratio to Rε=−1 was, the lower the absolute value of mean stress was. The mean stress relaxation occurred mainly in the initial stage and for the strain ratios more remotely from Rε=−1. The anelastic behavior of this alloy largely remained arising from the twinning and detwinning, with the strain ratio identified as an influential parameter via sensitivity analyses. The anelastic strain amplitude, along with three newly-defined parameters (eccentricity, angle deviation, and relative slope change) all decreased with increasing strain ratio, reflecting more symmetric hysteresis loops.

A study on the mean stress relaxation behavior of 2124-T851 aluminum alloy during low-cycle fatigue at different strain ratios

Strain-controlled fatigue tests of 2124-T851 aluminum alloy were performed under four strain ratios, R=−1, −0.06, 0.06 and 0.5. The fatigue test results indicated that the mean stress relaxation occurred under R≠−1. The mean stress relaxation rate was dependent on both the strain amplitude and strain ratio. In addition, fatigue life decreased with increasing strain ratio, especially at smaller strain amplitudes, which was attributed to mean stress and its relaxation during cyclic loading. Finally, based on the quantitative analyses of the mean stress relaxation behavior, a modified empirical model that can predict the mean stress relaxation at different strain ratios during fatigue was developed. The empirical model was then incorporated into the strain–life relationship to reflect the mean stress relaxation effects on fatigue life.

Strain ratio effects on low-cycle fatigue behavior and deformation microstructure of 2124-T851 aluminum alloy

The low-cycle fatigue tests of 2124-T851 aluminum alloy with strain ratios of −1, −0.06, 0.06 and 0.5 were conducted under constant amplitude at room temperature. Microstructural and fractographic examinations of the material after fatigue tests were performed by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. Firstly, the results showed that the material exhibited cyclic softening characteristic as a whole. The degree of softening decreased linearly with the increasing strain amplitude and the decreasing strain ratio. The lower fatigue life and ductility of the material corresponded to the larger strain ratios. Secondly, microstructure observations revealed that the density and length of slip bands increased with the increasing strain ratio at the given strain amplitude, and so did the volume fraction and size of coarse constituents, which were responsible for the reduction of fatigue life and ductility of the material. Finally, the SEM micrographs revealed that multiple crack initiation sites took place on the fracture surfaces at different strain ratios. The reduction of stable crack growth area with the increasing strain ratio was observed. Unstable crack growth region was only observed under R≠−1.

Deformation texture evolution of pure aluminum sheet under electromagnetic bulging

The deformation texture and microstructure evolution in pure aluminum sheet after electromagnetic bulging was investigated in detail by using electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques. It was found that the textural and microstructural developments were correlated with the complex strain path and the high strain rate. Stress–strain states from approximate uniaxial tension, non-equibiaxial tension to equibiaxial tension were experienced in the formed conical-shape workpiece along with the increasing strain ratio (i.e., the ratio between minor strain and major strain, representing the strain path of the formed workpiece). The grain orientation and distribution of boundary misorientation were found to be a function of the strain ratio, especially for the texture evolution in volume fraction of 〈110〉 fiber. A specific orientation with high Taylor factor, Rotated Goss 〈110〉, was observed and analyzed in terms of the contribution of preferable stress–strain state from the complex strain path and the assistance of high strain rate, which could increase the cross-slip activity, and eventually facilitate the texture development and induce more uniform microstructure.

Low cycle fatigue behavior of a semi-solid processed AM60B magnesium alloy

Strain-controlled low cycle fatigue tests were conducted on a thixomolded (semi-solid processed) AM60B alloy, and its fatigue life, fatigue parameters and cyclic deformation characteristics were evaluated. The microstructure consisted of primary α-Mg and network-like eutectic structure containing β-Mg17Al12 particles. The alloy showed basically symmetrical hysteresis loops in tension and compression and superior fatigue resistance to its die cast counterpart at lower strain amplitudes. The hysteresis loops exhibited a characteristic clockwise rotation, and the elastic modulus decreased with increasing strain amplitude. This was attributed to the non-linear (pseudoelastic) behavior stemming from twinning–detwinning. In comparison with extruded magnesium alloys, while the thixomolded alloy had less extensive twinning during cyclic deformation due to the presence of a large number of β-Mg17Al12 particles along with relatively small grain sizes, two types of twins (namely wider lenticular extension twins and narrower banded contraction twins) still occurred in some favorably oriented and relatively large primary α-Mg grains in the vicinity of fracture surface. With increasing strain ratio fatigue life decreased and the extent of mean stress relaxation increased. While the monotonic and cyclic yield strengths of this alloy were similar, the cyclic strain hardening exponent was higher than the monotonic strain hardening exponent.

The effect of residual stresses on fatigue of butt joints : Nguyen, T.N. and Wahab, M.A. Welding J. (1996) 75 (2), 55s–61s

The low-cycle fatigue tests of 2124-T851 aluminum alloy with strain ratios of −1, −0.06, 0.06 and 0.5 were conducted under constant amplitude at room temperature. Microstructural and fractographic examinations of the material after fatigue tests were performed by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. Firstly, the results showed that the material exhibited cyclic softening characteristic as a whole. The degree of softening decreased linearly with the increasing strain amplitude and the decreasing strain ratio. The lower fatigue life and ductility of the material corresponded to the larger strain ratios. Secondly, microstructure observations revealed that the density and length of slip bands increased with the increasing strain ratio at the given strain amplitude, and so did the volume fraction and size of coarse constituents, which were responsible for the reduction of fatigue life and ductility of the material. Finally, the SEM micrographs revealed that multiple crack initiation sites took place on the fracture surfaces at different strain ratios. The reduction of stable crack growth area with the increasing strain ratio was observed. Unstable crack growth region was only observed under R≠−1.