Increasing Strain Rate Research Articles

Microstructure evolution and fracture characteristics of GH4079 superalloy during high-temperature tensile process

An investigation of the thermal deformation characteristics and fracture mechanisms of the GH4079 superalloy was conducted through a series of hot tensile experiments conducted across a range of strain rates (from 0.01 s−1 to 1 s−1) and temperatures (from 970 °C to 1160 °C). The impact of MC carbides on the thermal deformation characteristics and dynamic recrystallization (DRX) of GH4079 superalloys, which are known for their challenging deformability, was analyzed to provide insights into enhancing the thermal workability of these formidable superalloys. The results suggest that DRX consistently preferentially occurs near MC carbides. The MC carbide plays a nucleation role in the particle-induced dynamic recrystallization mechanism, as determined via EBSD analysis. In addition, the primary grain boundary is the preferred nucleation site for DRX initiation. The promotion of DRX within the GH4079 alloy is considerably facilitated by the increased stored energy and nucleation site density resulting from the larger and more numerous carbides present at the grain boundaries. Moreover, the presence of carbides leads to uncoordinated deformation of the alloy during tensile deformation, which is also the induction factor of alloy cracking. With increasing strain rates and temperatures, the window of control over the hot deformation structure of the alloy diminishes. During the high-temperature deformation process of the GH4079 alloy, it is necessary to control the temperature within the range of approximately 1120 °C–1140 °C and the strain rate within the range of 0.1 s−1 to 1 s−1 to obtain a fine and uniform grain structure, delay material failure, and thus enhance the thermal processing performance of the material.

Dynamic compressive behavior of functionally graded triply periodic minimal surface meta-structures

Triply periodic minimal surface (TPMS) lattice structures have gained considerable attention because of their light weight, high strength, and excellent energy absorption capabilities. However, the effect of the amplitude that can control the topological morphology of a TPMS on the dynamic properties of the TPMS structure is not yet fully understood, as previous studies have focused on the relative density and size as well as their quasi-static mechanical properties. In this study, three types of uniform sheet-based TPMS structures with different amplitudes and three types of functionally graded sheet-based TPMS structures were proposed. Experiments and numerical simulations were conducted under quasi-static and dynamic loading conditions. Six types of TPMS lattice structures made of 316L stainless steel were manufactured via powder bed fusion. Quasi-static compression tests were performed at a strain rate of 0.001 s⁻¹. The experimental results indicate that increasing the amplitude can increase the elastic modulus, plateau stress, and energy absorption capacity of a structure. Moreover, the functional gradient amplitude structure has a higher energy absorption capacity, and the structures with line and log gradient strategies improved by 17.38% and 35.43%, respectively, compared to the uniform structure with an amplitude of 1. Additionally, an idealized rigid-linear plastic hardening (R-LPH) model was proposed to predict the mechanical response of the structures. The finite element method (FEM) was used to construct dynamic compression numerical models, and their validity was verified through split Hopkinson pressure bar (SHPB) tests at a strain rate of 695 s⁻¹. The mechanical response, deformation modes, and stress enhancement effects of the structures under dynamic compression were systematically studied. The results show that the mechanical performance and energy absorption capacity of the structures under dynamic impact loading increase with increasing strain rate. The critical velocity for the transition from the quasi-static mode to the impact mode increases with amplitude. For strain rates below 6000 s⁻¹, the strain rate effect is the main factor influencing the dynamic stress enhancement. As the strain rate continues to increase, the dynamic stress enhancement results from the combined effects of inertia and strain rate, with inertia effects gradually becoming the dominant factor. This study shows that functional gradient TPMS meta-structures have excellent mechanical and energy absorbing properties under quasi-static compression and dynamic compression, with potential applications in passive safety protection.

Rate-dependent mechanical and self-monitoring behaviors of 3D printed continuous carbon fiber composites

3D printed continuous carbon fiber reinforced polymer (CFRP) composites offer great advantages in structural health monitoring (SHM) owing to their flexibility in complex structure fabrication. Considering the many prospective aerospace applications, tensile experiments were designed to study their mechanical and self-sensing behaviors under a wide range of strain rates. The turning points in the resistance vs strain curves reveal the damage evolution of the specimens and divide the deformations into linear straining and damage evolution regions. Fiber elongation and fiber contact reduction dominate the resistance increase in the linear straining region and the resistance curve behaves linearly. But fiber breakage is the predominant factor in the damage evolution region, yielding a concave resistance curve. Strength, fracture strain, and resistance variation are found to display significant strain rate dependencies that increase with increasing strain rate. Numerous microcracks are formed and evolved into secondary cracks under dynamic loading. This process absorbs more strain energy and produces more carbon fiber breaks, sustaining a higher fracture strain and resistance variations. A model is developed to describe the strain- and strain rate- dependent resistance behaviors, and the predicted results agree well with experimental data. The outcomes of this work contribute to the application of 3D printed continuous CFRP composites in SHM.

Inertia effect of deformation in amorphous solids: A dynamic mesoscale model

Shear transformation (ST), as the fundamental event of plastic deformation of amorphous solids, is commonly considered as transient in time and thus assumed to be an equilibrium process without inertia. Such an approximation however poses a major challenge when the deformation becomes non-equilibrium, e.g., under the dynamic and even shock loadings. To overcome the challenge, this paper proposes a dynamic mesoscale model for amorphous solids that connects microscopically inertial STs with macroscopically elastoplastic deformation. By defining two dimensionless parameters: strain increment and intrinsic Deborah number, the model predicts a phase diagram for describing the inertia effect on deformation of amorphous solids. It is found that with increasing strain rate or decreasing ST activation time, the significant inertia effect facilitates the activation and interaction of STs, resulting in the earlier yield of plasticity and lower steady-state flow stress. We also observe that the externally-applied shock wave can directly drive the activation of STs far below the global yield and then propagation along the wave-front. These behaviors are very different from shear banding in the quasi-static treatment without considering the inertia effect of STs. The present study highlights the non-equilibrium nature of plastic events, and increases the understanding of dynamic or shock deformation of amorphous solids at mesoscale.

Three-dimensional mesoscale analysis of the dynamic tensile behavior of concrete with heterogeneous mesostructure

This paper investigates the dynamic tensile behavior of concrete under high strain rates. An optimized random concrete mesostructure generation procedure is established using the 3D entrance block (3D E(A, B)) algorithm to account for the intrinsic material heterogeneity. This approach avoids repetitive and complicated polyhedral aggregate overlapping checks in traditional methods, resulting in a highly efficient aggregate packing process. The nucleation, propagation, and coalescence of cracks are captured by a properly developed rate-dependent cohesive constitutive law. The mesoscale model is validated through comparison with experimental results. The crack evolution in the concrete under dynamic direct tensile loading conditions is explicitly presented, and the effects of the aggregate volume fraction and ITZ properties on the dynamic tensile strength enhancements are studied. The results indicate that material heterogeneity significantly influences the fracturing process and damage distribution. The dynamic tensile strength of concrete exhibits a two-strain rate regime dependence on the aggregate volume fraction concerning the strain rate. The influence of the mechanical properties of the ITZ on the dynamic tensile strength of concrete increases with the increasing strain rate.

Experimental Research on Dynamic Mechanical Properties of High-Density Foamed Concrete.

Foamed concrete is increasingly utilized in protection engineering because it offers a high energy absorption ratio and a relatively low construction cost. To investigate the dynamic properties of foamed concrete, a series of dynamic compression tests are carried out on high-density foamed concrete with densities of 800 kg/m3, 1000 kg/m3, and 1100 kg/m3 under a strain rate range of 59.05 s-1~302.17 s-1 by using a Φ-100 mm split Hopkinson pressure bar (SHPB) device. The effects of strain rate on the stress-strain relationship, dynamic compressive strength, and dynamic increase factor of foamed concrete are discussed in detail. The results show that the dynamic mechanical characteristics of foamed concrete with different densities exhibit a significant strain rate enhancement effect. Additionally, the energy absorption characteristics of foamed concrete are investigated, demonstrating that it can effectively prevent the transmission of incident energy and that its energy absorption efficiency declines as the strain rate increases. A high-speed camera was also employed to capture the failure process of foamed concrete. The results exhibit that fracture production and development induce the failure of foamed concrete, the failure process of foamed concrete advances as the strain rate increases, and the failure mode becomes increasingly severe.

Microstructural evolution and dynamic mechanical behavior of PM 2195 Al-Li alloy with resistance to shear instability in high strain rate deformation

The risk of adiabatic shear instability is common in traditional alloys covering high-strength steels, copper alloys and aluminum alloys during high strain rate deformation. However, the research on shear instability of 2195 Al-Li alloy prepared by powder metallurgy (PM) at high strain rates is still blank. The purpose is to explore its microstructure evolution and dynamic compression behavior. In this work, the 2195 Al-Li alloy prepared by PM amazingly demonstrates excellent resistance to shear instability at high strain rates during Split-Hopkinson pressure bar (SHPB) experiment. The microstructural evolution of grains and T1 (Al2CuLi) precipitate phase, and dynamic compression behavior of PM 2195 Al-Li alloy at various strain rates from 3000 s−1 to 9000 s−1 are investigated in detail employing correlative electron-backscatter diffraction (EBSD) and transmission electron microscopy (TEM). During high strain rate deformation, the alloy undergoes grain fragmentation and rotation, increasing dislocation density around the grains. When the strain rate is from 3000 s−1 to 7500 s−1, the Kernel Average Misorientation (KAM) value increases, indicating intensified localized strain. At a strain rate of 9000 s−1, a small number of grains are surrounded by nanocrystals (around 200 nm) that undergo stress release, while the average size of micrometer-sized grains is 0.81 μm. As the strain rate increases, the T1 phases in the alloy extends, vibrates, and fractures before dissolving in the matrix, while high-rate deformation promotes dislocation entanglement and defects, leading to the decomposition or ordering of precipitated phases through rapid plastic deformation. By virtue of energy dissipation strategy via the formation of nanocrystallines and dislocation behavior induced by the dissolution of T1 phases, the "positive-positive" effect is observed. The PM 2195 Al-Li alloy undergoes no shear failure even at the strain rate of 9000 s−1, showing great prospects in future applications in dynamic-loading conditions.

Mechanical properties and JC constitutive modification of tungsten alloys under high strain rates and high/low temperatures

The original Johnson-Cook model's poor prediction of W90 alloy stress at high strain rate and high and low temperatures restricts research and utilization of this alloy. This study used a Split Hopkinson Pressure Bar (SHPB) device to conduct dynamic compression tests on W90 alloy over a temperature range of [-90℃,700℃] and analyze its mechanical behavior. We examined the material's different plastic phase characteristics at high and low temperatures and conducted microstructure research on impact test specimens. Then, we analyzed the stress-strain data from SHPB experiments and quasi-static compression tests on the classical Johnson-Cook model. The original Johnson-Cook model was calibrated using the stress-strain data from SHPB and quasi-static compression tests, and the modified Johnson-Cook model was established and verified. The results show that: low temperature significantly strengthens the material's stress, while increasing temperature thermal softening reduces stress; increasing strain rate increases the strain generated by the workpiece, causing faster strain hardening and thermal softening effects, resulting in higher and more stable stress; low temperature makes thicker grain boundaries, increasing plastic stress, and increasing strain rate also increases plastic stress, as well as making the material's grain boundaries thicker. The increase of strain rate makes the grain more dense, which will also show up in the increase of stress on the macroscopic level; the modified Johnson-Cook model in this paper has high agreement with experimental data, with a mean value of MAPE of only 1.85 %,which is 90.20 % lower than the traditional model, and the average value of the RMSE is 85.56 % lower than the traditional model. The modified model significantly outperforms the traditional model in predicting stress and better describes stress changes in W90 at different temperatures.

Flow behavior and microstructural evolution of Al-1.2Mg-2.4Si-1.2Cu-0.6Mn alloy during hot compression

Thermal compression tests were conducted on Al-1.2Mg-2.4Si-1.2Cu-0.6Mn alloys with process parameters including deformation temperatures ranging from 400°C to 550°C and strain rates ranging from 0.05 s⁻¹ to 1 s⁻¹. The hot working properties of aluminum alloys were evaluated with intrinsic equations and machining diagrams. The results show that the processing safety zones of the alloy are 425–450℃ and 0.05–0.1 s−1, 450–475℃ and 0.1 s−1-0.5 s−1, and 475–500℃ and 0.5 s−1. The microstructure of the aluminum alloy following hot pressing was investigated through the use of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and backscattered electron diffraction (EBSD). When the deformation temperature of the alloy is below 450°C, the alloy organization exhibits a greater prevalence of inhomogeneous defects, which manifest as coarser granular regions in the micro-morphology. Upon reaching a deformation temperature of above 525°C, the deformed alloy organization exhibits an evident thermal cracking phenomenon. At the same temperature, an increase in strain rate is accompanied by a decrease in the Mg2Si phase and an increase in the precipitation of the Al(Fe,Mn)Si eutectic phase. Furthermore, the precipitated phase tends to become coarser. The presence of certain Mn-containing nanoparticle dispersions can impede the migration of subgrain grain boundaries, while simultaneously pinning dislocations and accelerating the generation of dislocation entanglement. This also can serve to inhibit the coarsening of the grains to some extent.

High strain rate tensile deformation of similar and dissimilar AA6082 and AA7075 friction-stir-welded blanks

Friction-stir-welding process has become an established solid-state technique for joining of dissimilar lightweight materials over the past decade by overcoming fundamental welding challenges such as solidification cracking, phase segregation and surface oxidation. Despite these unique capabilities, the resulting microstructure feature in the weld zone consisting of fine grains with a high dislocation density, challenges further heat treatment and forming processes. Hence, a high solution annealing temperature results in degradation of the adjusted microstructure and in a lower to reduced mechanical properties in case of dissimilar joints of precipitation-hardenable aluminum alloys. Subsequent hot forming therefore involves a great effort and requires further heat treatment steps. Thus, the present study investigates the effect of a recently introduced novel thermo-mechanical forming process on local deformation behavior of similar as well as dissimilar joints processed by friction-stir-welding technique of thin-walled AA6082 and AA7075 blanks. To avoid the complete elimination of the adjusted microstructure, the welding process is performed after a thermo-mechanical process consisting of solution annealing, die cooling and peak aging. Uniaxial tensile tests are then carried out at high strain rates ranging from ε˙ = 40 s-1 to ε˙ = 400 s-1. The results show an increase in yield and ultimate tensile strength as well as in total elongation after failure with increasing strain rates. As the strain rate increases, the flow stress of similar weld of AA7075 is higher than those of AA6082 and the dissimilar weld of AA6082 and AA7075. Local deformation measurements reveal higher strain localization in the welded zone for similar welds, which leads to micro-crack initiation and failure due to strain accumulation. Microstructure analysis shows very fine equiaxed grain structure in the nugget zone and homogenous distribution of precipitates after friction stir welding process, which explain the plastic deformation behavior.

The hot deformation behavior and processing map analysis of a high-nitrogen austenitic stainless steel

Understanding the hot deformation behavior of steel and establishing corresponding hot processing maps are crucial methods for determining appropriate hot processing parameters. In this article, the hot deformation behavior of a high-nitrogen austenitic stainless steel was investigated in the temperature range of 900–1150 °C and the strain rate range of 0.01–10 s−1 on a Gleeble-3500 thermo-mechanical simulator. The results show that the flow stress of experimental steel increases with decreasing deformation temperature and increasing strain rate. Based on the Arrhenius model, a constitutive equation was developed for the experimental steel, with a hot deformation activation energy of 603.347 kJ/mol. The hot processing maps were created employing the dynamic material model to determine the optimum hot processing conditions for the experimental steel at different strain levels.

Rift propagation signals the last act of the Thwaites Eastern Ice Shelf despite low basal melt rates

Abstract Rift propagation, rather than basal melt, drives the destabilization and disintegration of the Thwaites Eastern Ice Shelf. Since 2016, rifts have episodically advanced throughout the central ice-shelf area, with rapid propagation events occurring during austral spring. The ice shelf's speed has increased by ~70% during this period, transitioning from a rate of 1.65 m d−1 in 2019 to 2.85 m d−1 by early 2023 in the central area. The increase in longitudinal strain rates near the grounding zone has led to full-thickness rifts and melange-filled gaps since 2020. A recent sea-ice break out has accelerated retreat at the western calving front, effectively separating the ice shelf from what remained of its northwestern pinning point. Meanwhile, a distributed set of phase-sensitive radar measurements indicates that the basal melting rate is generally small, likely due to a widespread robust ocean stratification beneath the ice–ocean interface that suppresses basal melt despite the presence of substantial oceanic heat at depth. These observations in combination with damage modeling show that, while ocean forcing is responsible for triggering the current West Antarctic ice retreat, the Thwaites Eastern Ice Shelf is experiencing dynamic feedbacks over decadal timescales that are driving ice-shelf disintegration, now independent of basal melt.

Research on the splitting tensile dynamic mechanics performance of post-high-temperature high-performance concrete

High-performance concrete (HPC) structures were affected by secondary hazards after a fire, research on its dynamic mechanics performance is vital for assessing post-disaster structural safety. Therefore, the mechanism which governs impact of coupling among high temperature, cooling mode and strain rate on the splitting tensile mechanics performance of HPC was delved; impact factors including five temperatures, two cooling modes and four strain rates were designed; digital image technology (DIC) and hydraulic servo instrument were adopted to investigate the splitting tensile mechanics performance of HPC with Brazilian disc. Failure mechanical parameters of HPC under varying operational conditions and full-field deformation parameters of the whole loading process were obtained. As indicated by research result, the splitting tensile strength of test specimens cooled naturally from 200 °C to 600 °C was higher than that of specimens cooled rapidly, while the splitting tensile strength under natural cooling from 800 ℃ decreased by 6 % compared with rapid cooling. At the same temperature, splitting tensile strength of HPC was gradually increased with the increase of strain rate, and Dynamic Increase Factor (DIF) was significantly increased, showing relatively high rate sensitivity. With increasing temperature, the increase in DIF for HPC declined somewhat. As revealed by the result of DIC analysis, at high temperature, damage was relatively mild at the development stage and entered the stage of abrupt change of strain field in a short time. With increasing strain rate, the overall damage duration of test specimen was significantly shortened, and cooling mode exerted no significant impact on the development of splitting tensile damage in HPC. The criterion for splitting tensile dynamic strength of post-high-temperature HPC was put forward on the basis of J criterion. Meanwhile, an analysis by backscattered electron (BSE) on microstructure of HPC revealed mechanism which governs the impact of high temperature and cooling mode on the splitting tensile dynamic mechanics performance of HPC. The research result serves as a theoretical basis for calculating and assessing the post-fire structural dynamic response of HPC.

Nanosilica reinforced epoxy under super high strain rate loading

AbstractNanosilica reinforced epoxy‐matrix composites have been extensively investigated for higher mechanical strengths since its emergence, while few literatures are available about enhancement characteristics under super high strain rate loading, which is usually encountered during impact. Hereby, this work investigates the composites containing various kinds of nanosilica subjected to compression of strain rate higher than 20,000 s−1. A series of stress:strain curves are obtained and it is found that peak stresses increase with increasing strain rate along with silica fraction. Excitedly, the silica particle plays another enhancement role in anti‐localization of adiabatic shearing which occurs in pure epoxy, as indicated from abruptly dropped strain‐hardening index at ~22,000 s−1. A mechanism is proposed that uniformly distributed silica delays adiabatic shearing localizations to form through cracks, which is confirmed by fracture surface observance.Highlights Higher strain rate is achieved experimentally up to ~20,000 s−1. Strain rate effect is found on the peak stress of composites. Reinforcement of nanosilica is more distinct on strain‐hardening behavior. Silica particles hinder adjacent shearing localizations from abrupt evolution.

Effect of strain rate on nanoparticles and soot in counterflow flames of ethylene/ethanol and ethylene/OME3

This study delves into the impact of strain rate on soot and nanoparticle formation in counterflow diffusion flames (CDFs). While strain rate is generally known to reduce soot, understanding of nanoparticle formation remains limited. Strain rate (up to 207 s−1) effects in ethylene flames are here investigated along with ethanol and for the first time oxymethylene ether-3 (OME3). Ethanol and OME3 are well known to reduce particulate emission in several combustion conditions, however, especially for OME3, their effects at different strain rates lack comprehensive information. In soot-forming CDFs, two distinct zones emerge: a pyrolytic zone from the fuel nozzle to the stagnation plane (S.P.), and an oxidative zone from the oxidizer nozzle to the S.P., analogous to the centerline and wings of a coflow diffusion flame. The study aims to unravel the intricate relationship between strain rate, oxygenated fuel, and soot and nanoparticle formation in these two zones. Laser-induced fluorescence, attributed to nanoparticles, laser-induced incandescence, attributed to soot, and scattering were used to track particle formation. Both nanoparticles and soot are formed in both pyrolytic and oxidative zones, with smaller sizes in the former, emphasizing dominant nucleation and coagulation processes. Findings indicate a general particle reduction with strain rate for all the fuel blends, suggesting an inhibition effect on particle nucleation and growth. The effect of strain rate differs for pyrolytic and oxidative zones, with particle reduction in the pyrolytic zone slightly more sensitive to strain rate due to lower kinetic timescales present in this zone of the flame. Oxygenated fuels generally decrease particle formation, however, in pyrolytic zones a slight increase of nanoparticles can be detected. This effect is more evident at low strain rates, and it disappears as strain rate increases. OME3 exhibits higher reactivity and lower sensitivity to strain rate. The insights from this study contribute to developing cleaner combustion technologies, especially in blending oxygenated fuels with traditional ones. Further research is recommended for broader applicability, considering high strain rates and a wider range of dilution conditions.

Crushing responses and energy absorption characteristics of the dynamic stiffening porous material subjected to different strain rates

Porous material (PM) has excellent energy absorption performance and is widely used as an impact-energy absorber. However, the PM may provide little utility when the impact conditions change. Shear stiffening gel (SSG) with an extremely strong viscosity effect can be as a dynamic responding fortifier to overcome the limitation of PMs. In this paper, a rate-dependent, smart energy-absorbing material (SSG/PM) is fabricated by incorporating SSG that is reinforced with CaCO3 particles onto the PM. Aided by the dynamic compression experiments at the strain rate range of 0.001 to 100 s−1, both SSG/PM and neat PM are assessed and compared for crushing performance. Results reveal that the SSG/PM exhibits a pronounced dynamic stiffening characteristic in response to various strain rates owing to the rate-dependent phase transition of embedded SSG, thereby contributing to enhancing the PM skeleton's ability to withstand deformation. The SSG/PM displays a noteworthy boost in energy absorption (up to 831.98 %). Moreover, the influence of loading rate, particle mass fraction, and PM aperture size are also examined. The findings indicate that its crushing resistance and energy absorption capability are enhanced with the increase in strain rate, demonstrating the ability to adapt to various dynamic scenarios. The use of a higher particle mass fraction and smaller aperture size helps to improve the energy absorption capability of the SSG/PM. Additionally, quantitative energy analysis is implemented in which the energy dissipation mechanisms of the SSG/PM are attributed to the synergistic interaction of skeleton deformation, shear stiffening effects, and particle enhancement. It is ascertained that as the loading rate increases, the shear stiffening effect continues to strengthen; the particle content effect exhibits a rising-falling trend; while the skeleton deformation shows a rate-independent feature. This study sheds light on the crushing behaviors and corresponding energy dissipation mechanisms of SSG-based composites, thereby providing valuable insights for the design of SSG-based composites.

Evaluation of Left Ventricular Remodeling and Prognosis after PCI in Acute Myocardial Infarction Using Real-Time, Three-Dimensional Echocardiography Combined with Layer-Specific Strain Imaging

Aim: This study aimed to evaluate left atrial and left ventricular volumes, strains, and strain rates in patients with acute ST-segment elevation myocardial infarction (STEMI) treated with percutaneous coronary intervention (PCI) using real-time three-dimensional echocardiography and layer-specific strain techniques. The relationships between these parameters and left ventricular remodeling (LVR) and prognosis were also explored. Methods: The study included 217 patients with first-episode STEMI who underwent emergency PCI. Echocardiography and myocardial strain analyses were performed within 24 h post-PCI. Patients were categorized into early and non-early LVR groups based on the increase in left ventricular end-diastolic volume (LVEDV). The occurrence of major cardiovascular adverse events (MACE) was followed up for one-year post-PCI. Differences in clinical data and ultrasound parameters between the groups were compared, and the predictive value of myocardial strain indicators for late LVR was analyzed using a multivariate logistic regression model and receiver operating characteristic (ROC) curves. Results: Early LVR occurred in 54.8% of patients and was characterized by decreased left ventricular systolic function, more segments with abnormal movement, and reduced absolute strain values in the three layers of the left ventricular wall myocardium, with a compensatory increase in left atrial strain rate during the contraction phase. The early LVR group showed a higher incidence of MACE at the one-year follow-up. At 6 months post-PCI, 29.9% of patients developed late LVR, which was not completely related to early LVR. Late LVR was associated with a higher incidence of MACE. The longitudinal strain value of each layer of left ventricular myocardium obtained from layer-specific strain imaging showed predictive value for advanced LVR. Conclusions: More than half of patients with STEMI develop early LVR post-PCI, with a higher incidence of MACE during one-year of follow-up, necessitating attention to early LVR in clinical practice. Late LVR, which develops in some patients after 6 months, is also linked to a higher incidence of MACE. Accurate monitoring of the myocardial deformation function using layer-specific strain imaging is expected to become a reference indicator for clinical diagnosis and treatment. Monitoring the structure and function of the left atrium and mitral valve alongside the LVR is important for prognostic assessment and for formulating diagnostic and treatment plans.

Effect of the strain rate on the deformation mechanisms of TWIP-type steel

This paper describes the influence of the strain rate on the microstructure of X55MnAl25-5 steel from the group of high-manganese steels exhibiting the twinning-induced plasticity effect. The tests were carried out at a wide range of strain rates, starting with static tensile tests where the appropriate strain rates were 0.005 s−1, and ending with tests using a flywheel machine at strain rates of 1830 s−1 and 4650 s−1. The increase in the applied strain rate on the example of the tested steel results in hardening. Evolutionary changes leading to the predominance of dislocation slipping over the twinning are observed in the microstructure under static deformation conditions. The increase in the intensity of twinning with the simultaneous decrease in the mobility of dislocations progresses as the strain rate increases. The microstructure evolution was characterized using light optical microscopy and scanning electron microscopy, including electron backscatter diffraction. The qualitative analysis of the deformation twins was performed. For the lowest strain rate, 5·10−4 s−1, deformation twins appear in a single twinning system, while increasing the strain rate leads to the activation of multiple twinning systems. Proceeding to the range of dynamic tests reveals an increase in the participation of the twinning mechanism in the deformation of the examined steel. With an increasing strain rate, the effect of texture on the twinning process activity decreases. Based on the obtained results, a diagram was elaborated that presents the microstructural changes which take place in X55MnAl25-5 steel after deformation under static and dynamic tensile conditions in graphical form.

Effects of high temperature and strain rate on the impact-induced inter-laminar shear behavior of plain woven CF/PEEK thermoplastic composites

This paper aims to investigate the interlaminar shear properties and failure mechanisms of plain woven carbon fabric/polyetheretherketone (CF/PEEK) thermoplastic composites under high strain rate impact loads at different temperatures (25°C, 120°C, 295°C). A reliable hot air flow heating method with SHPB is creatively employed for short beam shear experiments. A multi-scale model was developed to predict the impact behavior of plain CF/PEEK composites. Both results show that the thermoplastic composites have strong strain rate and temperature dependence, and which are more sensitive to temperature effect. As the temperature increases, the thermoplastic composites are mainly affected by the softening effect of the matrix due to the glass transition temperature. The shear modulus and peak stress appear to decline at high temperatures, while the failure strain tends to increase. The damage mode changes from interlayer delamination cracking at the glassy state to shear fracture and fiber pullout at a highly elastic state. As the strain rate increases, the failure strain decreases, while the shear modulus and peak stress show the opposite trend. Fiber bundle breakage, debonding, matrix cracking, and significant interlayer delamination occur at high strain rates.

Exploring the strain rate influence on shear yield behavior of acrylonitrile-butadiene-styrene: Experimental and numerical study

Most experimental and numerical studies are limited to examining the effect of strain rate on the compressive and tensile yield behavior of Acrylonitrile-Butadiene-Styrene (ABS), an amorphous material of significant industrial relevance, rather than its shear yield behavior; therefore, this study is dedicated to addressing this notable gap in the literature by exploring the effect of strain rate on the shear yield behavior of ABS. To this end, shear tests were carried out using the Wyoming version of the Iosipescu (V-notched) shear test fixture at five distinct loading rates, ranging from 5 × 10−3 to 1 × 101 mm/s, which correspond to strain rates between 5.5 × 10−4 s−1 and 7 × 10−1 s−1. Shear strain distributions in the specimens were measured using the Digital Image Correlation (DIC) technique. The shear test results not only revealed a substantial increase in the shear yield strength of ABS with increasing strain rate, but also demonstrated that the shear yield strength of ABS is more sensitive to strain rate than its compressive and tensile yield strengths. The findings of the study also suggested that using shear-tension test data pairs at the same strain rates is more effective for determining the hydrostatic pressure sensitivity parameter than using tension-compression and shear-compression test data pairs. The experimental results were validated against numerical predictions obtained through finite element analyses employing an elastic-viscoplastic constitutive model, which comprehensively accounted for non-linear material properties, geometric complexities, and non-linearities arising from boundary contacts.