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Based on mechanical tensile experiments on the CoCrFeNi high-entropy alloy (HEA), this study explores the forming patterns of the eccentrically shaped sub-hemispherical lined explosively formed projectile (EFP) made of the HEA material. The CoCrFeNi HEA material is initially prepared, and mechanical tensile tests are conducted at various temperatures and strain rates. The Johnson–Cook (J–C) constitutive equation for this material is derived by fitting the experimental data. Scanning electron microscopy and the energy dispersive spectrometer characterize the fracture surface of the tensile specimens, providing insights into the mechanical ductility and fracture mechanism of CoCrFeNi HEA. The EFP forming process under various charge configurations is simulated using AUTODYN software, leading to the identification of the optimal charge configuration. In addition, the damage performance is evaluated. This study provides a theoretical basis for applying HEA materials in the field of shaped charges and offers new ideas and methods for designing more efficient shaped charge warheads. [ABSTRACT FROM AUTHOR]

One of the most important issues related to the strength of metals is the strain rate sensitivity of the flow stress. In this study, an analytical model of the flow stress as a function of strain rate is derived theoretically. The model can reproduce the strain rate sensitivity of the flow stress of copper over a wide range of strain rates (up to 109 s−1) quantitatively. Our theoretical derivations indicate that the strain rate sensitivity of the flow stress, especially that above 103 s−1, is a result of both the variation of the dislocation mobility mechanism with stress and the particular stress dependence of dislocation density but is not a result of each single mechanism. In particular, the stress dependence of the dislocation density and the initial dislocation density are critical to the quantitative relation of the flow stress–strain rate at high strain rate and the strain rate threshold, under which the upturn of the flow stress occurs, respectively. Moreover, experiments with copper of different initial dislocation densities at moderate and high strain rate are performed. The strain rate threshold of the flow stress upturn observed in the experiments grows considerably as initial dislocation density increases, which is in accordance with theoretical prediction by our model. [ABSTRACT FROM AUTHOR]

Additive manufacturing has the potential to repair high value components, saving significant time and resources; however, the level of reliability and performance of additive repairs is still relatively unknown. In this work, the structure–property and performance of laser wire additive manufacturing repairs in 1100 aluminum are investigated. Two types of intentional damage are inflicted on the samples and subsequently repaired with pulsed laser deposition additive manufacturing. Quasi-static (10 − 3 s − 1 ) and high strain-rate (10 − 3 s − 1 ) mechanical testing is carried out with in situ diagnostics and post-mortem imaging. The results show that while the quasi-static strength and ductility of samples with a repaired region are lower than a pristine sample, the dynamic strength under shock loading is comparable. This work highlights both the potential utility of additive manufacturing for repair purposes, the significant risk of compromised performance of additive parts under specific conditions, and the need to test at varying strain rates to fully characterize material performance. [ABSTRACT FROM AUTHOR]

Shock invariant relationship, which was conceived for inert shock waves to derive the 4th power relationship between shock pressure and maximum strain rate, is generalized for reactive shock waves such as Chapman–Jouget detonation and shock-induced vaporization. The generalization, based on the first-order reaction models, is a power function relationship between overall dissipated energy (Δ e d i s ) and reaction time Δ τ such that Δ e d i s Δ τ 1 / α = constant , where the power coefficient α is found to be in the range of 2/3–4. Experimental data, though scarce, are consistent with the generalization. Implication of the generalization for inert shocks is also considered and suggests a broad range of the 4th power coefficient including an inequality equation that constrains the shock and particle velocity relationship. [ABSTRACT FROM AUTHOR]

Shock experiments are widely used to understand the mechanical and electronic properties of matter under extreme conditions. However, after shock loading to a Hugoniot state, a clear description of the post-shock thermal state and its impacts on materials is still lacking. We used diffraction patterns from 100-fs x-ray pulses to investigate the temperature evolution of laser-shocked Al–Zr metal film composites at time delays ranging from 5 to 75 ns driven by a 120-ps short-pulse laser. We found significant heating of both Al and Zr after shock release, which can be attributed to heat generated by inelastic deformation. A conventional hydrodynamic model that employs (i) typical descriptions of Al and Zr mechanical strength and (ii) elevated strength responses (which might be attributed to an unknown strain rate dependence) did not fully account for the measured temperature increase, which suggests that other strength-related mechanisms (such as fine-scale void growth) could play an important role in thermal responses under shock wave loading/unloading cycles. Our results suggest that a significant portion of the total shock energy delivered by lasers becomes heat due to defect-facilitated plastic work, leaving less converted to kinetic energy. This heating effect may be common in laser-shocked experiments but has not been well acknowledged. High post-shock temperatures may induce phase transformation of materials during shock release. Another implication for the study is the preservability of magnetic records from planetary surfaces that have a shock history from frequent impact events. [ABSTRACT FROM AUTHOR]

The primary objective of the present investigation is to elucidate the operative micromechanisms influencing the strain rate sensitivity and activation volume in (FeCrNi)99Si1 and FeMnNi medium-entropy alloys. Room-temperature nanoindentation experiments at different loading rates were performed to study the evolution of the strain rate sensitivity and activation volume in (FeCrNi)99Si1 and FeMnNi medium-entropy alloys. The (FeCrNi)99Si1 samples were subjected to plane strain deformation by rolling at 77 and 300 K to study the effect of temperature on the strain rate sensitivity, while the FeMnNi and (FeCrNi)99Si1 samples were subjected to simple shear deformation by high-pressure torsion at 300 K to examine the effect of strains. Contrary to the well-documented trend observed in fcc metals and alloys, where the strain rate sensitivity typically increases with decreasing grain size, the present study reveals a distinct behavior for the current alloys. Similarly, these alloys are characterized by extremely low activation volumes of a few tens of b3 compared to 100–1000 b3 for conventional fcc metals and alloys in the microcrystalline grain size regime. Unlike conventional fcc metals and alloys, there is an insignificant change in the activation volume of the current high-/medium-entropy alloy (H/MEA) with decreasing grain size from the microcrystalline to nanocrystalline regime. The unique evolution of strain rate sensitivity and activation volume in H/MEAs is explained in terms of the evolution of distinct dislocation structures as well as synergistic operation of additional mechanisms such as twinning, phase transformation from fcc to hcp phases, cluster strengthening, and short-range ordering due to the aperiodic energy landscape existing in MEAs. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) have attracted widespread attention from scholars as a new type of material employed in extreme environments. However, as a main kind of HEAs, many face-centered cubic single-phase HEAs are restricted in industrial applications due to their lower yield strength and high cost when containing expensive elements such as Co. In this study, dispersion strengthening by heat treatment was introduced in low-cost Co-free Fe40Mn20Cr20Ni20 HEA to improve its strength, and its high-temperature tensile behavior and constitutive model were studied to explore its potential application at high temperatures. It is found that when subjected to quasi-static room-temperature stretching, the heat-treated sample exhibits a yield strength of 534 MPa and a tensile plasticity of 26.8%. In addition, the tensile behavior of samples after heat treatment was investigated at high temperature (573–873 K) and low strain rate (10−3–10−1 s−1). The results suggest that the yield strength decreases with increasing temperature and decreasing strain rate. Moreover, at 873 K and 10−3 s−1, the electron backscatter diffraction system and x-ray diffraction results of the deformed sample indicate that the softening curve is driven from the recovery of materials. Finally, the flow stress was predicted using the Arrhenius equation and Artificial Neural Network model (ANN), and the two models were assessed using the average absolute relative error and coefficient of correlation (R). The results showed that the ANN had higher accuracy. [ABSTRACT FROM AUTHOR]

Understanding of dynamical responses and mechanical characteristics of metals and alloys at high strain rates holds significant importance in fundamental physics and optimizing the performance capabilities of materials. During high-speed impact scenarios, materials may be subjected to high pressure and plastic deformation, which have the potential to modulate their mechanical attributes. In this study, high-speed planar impact experiments were conducted to investigate the progressive alterations in the microstructures and mechanical properties in coarse-grain body-centered cubic (bcc) iron subjected to high-strain-rate (approximately 2.60–3.89 × 106 s−1) impact reaching approximately 15 GPa in a one-stage light-gas gun. The nanoindentation tests show that the nano-hardness of the post-shock iron improves 1.5 times from approximately 1.75–2.70 GPa. Microscopic analyses of the post-shock bcc-iron show no significant grain refinement but a noticeable increase in the twin boundaries (TBs) and low angle grain boundaries (LAGBs) proportion with increasing shock pressure. Therefore, the interaction between TBs, LAGBs, and dislocations in post-shock iron grains plays an important role in mediating its mechanical properties. Our findings serve as possible guidance for exploring the mechanical properties of single-crystalline and poly-crystalline iron-based materials, such as steel, with optimized mechanical performance. [ABSTRACT FROM AUTHOR]

Grafting polymer chains to the surface of nanoparticles overcomes the challenge of nanoparticle dispersion within nanocomposites and establishes high-volume fractions that are found to enable enhanced material mechanical properties. This study utilizes coarse-grained molecular dynamics simulations to quantify how the shear modulus of polymer-grafted nanoparticle (PGN) systems in their glassy state depends on parameters such as strain rate, nanoparticle size, grafting density, and chain length. The results are interpreted through further analysis of the dynamics of chain conformations and volume fraction arguments. The volume fraction of nanoparticles is found to be the most influential variable in deciding the shear modulus of PGN systems. A simple rule of mixture is utilized to express the monotonic dependence of shear modulus on the volume fraction of nanoparticles. Due to the reinforcing effect of nanoparticles, shortening the grafted chains results in a higher shear modulus in PGNs, which is not seen in linear systems. These results offer timely insight into calibrating molecular design parameters for achieving the desired mechanical properties in PGNs. [ABSTRACT FROM AUTHOR]

Extending the storage-recovery model, we propose a new strengthening model, premised on detailed evolution laws for both mobile and immobile dislocations, for metals under moderate to intense loading. These dislocation density evolution laws include the multiplication, storage under the effect of dislocation junctions, release of pinned dislocations, and annihilation by cross-slip. The storage-release description is derived from a simplified depiction of the probability distribution function of the dislocation length in dislocation networks. Although the model requires only few parameters to characterize the evolution of dislocation densities, remarkable agreement is found with available experimental data. From a theoretical study of the long-time behavior of the model, analytical expressions are provided to easily extract most of these parameters from experimental stress–strain curves in the quasi-static regime, whereas the parameter that governs the strength of the release process is adjusted from dynamic tensile tests. Their values so determined for polycrystalline tantalum allow the model to reproduce experimental plate-impact data with a very good match. [ABSTRACT FROM AUTHOR]

The compression-induced structural transition (ST) and grain refinement of BCC Fe nanowires have been investigated based on atomistic simulations. It is found that high strain rate compression can cause nanowires to reach higher pressures and meet ST conditions, and the threshold stress of ST is found to be much lower than that of bulk materials. Thus, the compression process of nanowires at high strain rates includes elastic deformation, ST and its reverse process, grain refinement, and buckling instability. The occurrence of grain refinement is due to the fact that after undergoing ST and its reverse process, the (001) cross section of the nanowire can be transformed into different (111) planes. Furthermore, the dependence of stress threshold and nucleation structure on strain rate is revealed. When the strain rate increases to a certain threshold, HCP nucleation is found to occur on the side surface of the nanowire, but its reverse process will quickly occur due to the pressure release on the side. With the strain rate increase, the stress threshold of ST no longer satisfies a constant power-law change, and the power-law index will increase. When the strain rate exceeds 5 × 1010 s−1, the elastic deformation prior to ST also exhibits strong nonequilibrium characteristics, causing a sharp increase in the number of HCP nuclei. Especially, the nanowires will ultimately be in a disordered state, rather than a nanocrystalline structure. Also, the cylindrical and prismatic nanowires are both considered to understand the influence of boundary morphology, and the differences in nucleation and the similarity in deformation are explained. Note that, as the strain rate increases, the cylindrical nanowires undergo HCP nucleation directly, while the prismatic nanowires undergo significant twinning deformation first. [ABSTRACT FROM AUTHOR]

We outline a coarse-grained model of epoxy resins (bisphenol-F-diglycidyl-ether/3,5-diethyltoluene-2,4-diamine) to describe elastic and plastic deformation, cavitation, and fracture at the μm scale. For this, molecular scale simulation data collected from quantum and molecular mechanics studies are coarsened into an effective interaction potential featuring a single type of beads that mimic 100 nm scale building blocks of the material. Our model allows bridging the time–length scale problem toward experimental tensile testing, thus effectively reproducing the deformation and fracture characteristics observed for strain rates of 10−1 to 10−5 s−1. This paves the way to analyzing viscoelastic deformation, plastic behavior, and yielding characteristics by means of "post-atomistic" simulation models that retain the molecular mechanics of the underlying epoxy resin at length scales of 0.1–10 µm. [ABSTRACT FROM AUTHOR]

Additive manufacturing has the potential to repair damaged parts, but the performance of additive materials under high strain rate loading is still uncertain—especially with the added complexity of an interface with an existing wrought material. In this work, 304L stainless steel samples were intentionally damaged and then repaired with wire-fed laser additive manufacturing. The samples were subjected to shock loading to generate incipient spall. Velocimetry and post-mortem metallography results show that when the additive repair process parameters are optimized to reduce porosity and match the equation of state of the original material, the influence of the repair region on the shock propagation is negligible. The free-surface velocity profile and internal damage morphology of the repaired sample are shown to be practically identical to the pristine material. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were used to analyze the mechanical properties and failure processes of poly(p-phenylene-terephthalamide) (PPTA), poly(p-phenylene-benzimidazole-terephthalamide) (PBIA), PBIA–PPTA (formed by 1:1 copolymerization of PPTA and PBIA), and poly(p-phenylene-benzobisoxazole) (PBO) crystals at different strain rates and temperatures. The failure stress and strain were found to be linear with the temperature and logarithmic strain rate. Moreover, based on the kinetic theory of fracture and the comprehensive simulation results, we formulated a model that describes the failure stress of the aforementioned crystals under varying strain rates and temperatures. Through the analysis of the failure process, we found that in PPTA, PBIA, and PBIA–PPTA crystals, the bond failure probability is correlated with the strain rate and temperature. The examination of bond lengths and angles unveiled that bonds with larger initial aligning angles are more susceptible to failure during the strain process. Intriguingly, the stretching process induced a conformational change in the PBO molecular chain, leading to a deviation from the linear relation in its stress–strain curve. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement behavior of Ni–Cr–Mo-based superalloy fabricated by wire arc additive manufacturing (WAAM) with or without solution treatment was investigated by electrochemical hydrogen charging. The results show that the dissolution of the Laves phase promotes the precipitation of the δ phase in the matrix of WAAM superalloy after solution treatment at 980 °C. When the solution temperature goes up to 1080 °C, the large Laves phase disappears and only MC exists in the matrix. The interfaces between the Laves phase/δ phase and matrix generally could act as hydrogen traps, which would reduce the motion of hydrogen and lead to high hydrogen embrittlement resistance of the WAAM and ST-980 °C samples. However, hydrogen mainly accumulates on grain boundaries in the ST-1080 °C due to the disappearance of the Laves phase and δ phase. Hydrogen-induced intergranular brittle fracture occurs during the slow strain rate tensile test and the ST-1080 °C samples exhibit higher hydrogen embrittlement susceptibility than that of the WAAM and ST-980 °C samples. • The solid solution changes the element distribution and precipitates in the WAAM superalloy. • The effect of hydrogen on the mechanical properties of the WAAM superalloy was investigated. • The hydrogen diffusion in the WAAM superalloy is affected by dendrite, Laves phase and δ phase. • The fracture mode of the hydrogen-containing WAAM superalloy is different under different solid solution temperatures. [ABSTRACT FROM AUTHOR]

In the context of the growing use of hydrogen for decarbonization in combustion, understanding NO x emissions from hydrogen burners is crucial. This study focuses on the impact of partial premixing on NO x production in hydrogen flames using a coaxial injector with swirl. The goal is to expand conventional jet scaling laws to encompass additional physical phenomena. The flexible injection system employed allows the stabilization of various flame types depending on the operating conditions, and double-front flames are obtained in several configurations. Observing the limitations of known scaling laws, particularly in coaxial flows with low-velocity differences or swirl, we conduct experiments measuring NO x and flame volume. Two Large Eddy Simulations explore distinct flame configurations to deepen our understanding about coaxial jet and recirculating flames, especially in the presence of a secondary premixed front due to rich premixing. Our investigation delves into the relationship between NO production and strain rate, considering turbulent and strain-related timescales. Notably, the presence of a premixed flame front alters the velocity profile on the shear layer, and the observed relationship between strain and turbulence in jet flames does not hold for recirculating flames. Thanks to this new insight, we propose a novel formulation for NO x scaling in coaxial jets, leveraging existing literature on coaxial jet modeling. Additionally, we propose a simple model to represent the piloting strain rate for NO emission in recirculating flames. Intricate effects of both swirl and partial-premixing are then included in the derived NO x scaling laws. [Display omitted] • Nitrogen oxide (NO x) emissions are measured in many swirled hydrogen flames. • Large-eddy simulations are used to enlighten the formation mechanisms. • Scaling laws for NO x emissions are derived to work for different flame topologies. [ABSTRACT FROM AUTHOR]

The Ganzi‐Yushu fault (GYF) is one of the most seismically active fault systems in eastern Tibet, having experienced five M > 7.0 earthquakes over the past 300 years. Here, we use Sentinel‐1 InSAR data spanning from 2014 to 2023 to derive the interseismic velocity fields along the GYF. We calculate the strain rate fields for the entire fault system, which reveal localized strain accumulation along the GYF as well as along two secondary faults within the Bayan Har block. The inversion results obtained from the elastic block model indicate left‐lateral strike slip rates of 4.0–6.5 mm/yr along the GYF and five locked segments distributed along strike. Furthermore, we identify two shallow creeping segments on the InSAR velocity maps. Based on the locations of the creeping sections and their temporal decay characteristics, we infer that the shallow creep along the GYF is afterslip of the 2010 Yushu earthquake. Plain Language Summary: The 500 km‐long Ganzi‐Yushu fault is a main fault system in eastern Tibet. Investigating its slip behavior is crucial for assessing earthquake potential and understanding the deformation patterns in the region. Using space geodetic observations, we investigate the slip rate distribution along the Ganzi‐Yushu fault. The energy accumulation along the fault can be divided into five segments, which correspond remarkably well with the historical events. Besides the Ganzi‐Yushu fault, we find that two secondary faults within the Bayan Har block, which had not received much attention before, also exhibit significant seismic hazard. We identify two shallow creeping sections along the fault. By analyzing the spatio‐temporal characteristics of the shallow creeping sections, we confirm that they are associated with postseismic activity of the 2010 Yushu earthquake. Our results give insights into the regional deformation mode and seismic hazard. Key Points: Our large‐scale high‐resolution InSAR velocity fields reveal strain accumulation within the Bayan Har blockThere are five locked segments distributed along the Ganzi‐Yushu fault, which corresponds well with historical eventsWe identify two transient shallow creeping segments associated with afterslip of the 2010 Yushu earthquake [ABSTRACT FROM AUTHOR]

Highlights This study investigates the relationship between microstructure and mechanical properties of carbon fiber reinforced epoxy composites, specifically in the context of lightweight hydrogen storage pressure vessels manufactured by the filament winding process. The filament winding technique often introduces variability in fiber orientation and porosity which can lead to inconsistencies in mechanical properties. By investigating the influence of dynamic loading over a range of strain rates, from quasi‐static to 100 s−1, this research aims to understand the effects of different fiber orientations (±15° and ±30°) and multilayer structures on the performance of these composites. Using a custom‐designed Interrupted Dynamic Tensile Test (IDTT) apparatus, we investigated how damage mechanisms evolve during rapid tensile deformation. The results showed that porosity has a significant impact on mechanical performance, particularly at high strain rates, where cracks initiate at pores and propagate via fiber/matrix decohesion and fiber breakage. These microstructural defects contribute to mesoscopic failure mechanisms such as transverse cracking and micro‐delamination between composite layers. The mechanical properties were found to be strain rate sensitive, with visco‐damage phenomena playing a critical role in determining the damage evolution under dynamic loading. These findings provide important insights into the design and optimization of hydrogen storage vessels, highlighting the importance of controlling porosity and understanding the response of the composite to varying strain rates for improved durability and performance. Comprehensive analysis of dynamic loading. Influence of fiber orientation and porosity on mechanical integrity. Visco‐damage and failure mechanisms under high strain rates. [ABSTRACT FROM AUTHOR]

Pressure solution is inferred to be a significant contributor to sediment compaction and lithification, especially in carbonate sediments. For a sediment deforming primarily by pressure solution, the compaction rate should be directly related to the rate of calcite dissolution, transport along grain contacts, and calcite reprecipitation. Previous experimental work has shown that there is evidence that deformation in wet calcite grain packs is consistent with control by pressure solution, but considerable ambiguity remains regarding the rate limiting mechanism. We present the results of laboratory compaction experiments designed to directly measure calcite dissolution and precipitation rates (recrystallization rates) concurrently with strain rate to test whether measured rates are consistent with predicted rates both in absolute magnitude and time evolution. Recrystallization rates are measured using trace element chemistry (Sr/Ca, Mg/Ca) and isotopes (87Sr/86Sr) of fluids flowing slowly through a compacting grain pack as it is being triaxially compressed. Imaging techniques are used to characterize the grain contacts and strain effects in the post-experiment grain pack. Our data show that calcite recrystallization rates calculated from all three geochemical parameters are in approximate agreement and that the rates closely track strain rate. The geochemically inferred rates are close to predicted rates in absolute magnitude. Uncertainty in grain contact dimensions makes distinguishing between surface reaction control and diffusion control difficult. Measured reaction rates decrease faster than predicted from standard pressure solution creep flow laws. This inconsistency may indicate that calcite dissolution rates at grain contacts are more complex, and more time-dependent, than suggested by geometric models designed to predict grain contact stresses. [ABSTRACT FROM AUTHOR]

The behavior of materials under high strain rates is pivotal to their deformation during machining processes. This research focuses on numerical modeling of the dynamic behavior of aluminum alloys (AA) 7075-T6 in dry turning operation. The Johnson–Cook (J-C) constitutive equation and coefficients derived from the split-Hopkinson pressure bar (SHPB) and uniaxial tensile tests were used in numerical simulations based on finite element (FE). Numerical models were validated under different machining conditions. The numerical and experimental studies revealed the significant impact of the feed rate on the alloy's behavior, chip thickness, and chip morphology. The work confirmed that increasing the cutting speed and feed rate led to higher machining temperatures. The lowest amounts of built-up layer (BUL) and built-up edge (BUE) were observed at high cutting speed and feed rate levels. The minimum surface roughness was recorded at low feed rates and high cutting speeds. The experimental results adequately confirmed the accuracy of the FE simulations. This research indicates that strain rate hardening significantly affects AA 7075-T6 and substantially increases strength as the strain rate increases. The results of the machining simulation validated the appropriateness of the J-C damage parameters used for the material. [ABSTRACT FROM AUTHOR]

Concrete's dynamic performance and energy dissipation are critical areas of interest that are significantly influenced by strain rate and aggregate content. This study investigated concrete's dynamic deformation, strength development and energy dissipation characteristics from specimens containing 0, 32%, 37% and 42% aggregate. These specimens were subjected to impact compression tests using a split Hopkinson compression apparatus, which allowed the effects of strain rate and aggregate content on the deformation, strength and energy dissipation of the concrete to be analysed. The results show that the concrete exhibits deformation hysteresis under impact loading, with splitting tensile failure as the predominant damage mechanism. Dynamic strength was more sensitive to strain rate than aggregate content. The dynamic increase factor (DIF) varied with aggregate content at different strain rates. The extent of specimen damage significantly influenced the energy distribution ratio, with absorbed energy showing a more pronounced strain rate effect than transmitted and reflected energy. Conversely, the amount of transmitted energy had a more pronounced impact on aggregate content than the amount of absorbed and reflected energy. [ABSTRACT FROM AUTHOR]

In this study, Cu–10W and 2 wt%Y 2 O 3 /Cu–10W composites were successfully prepared via mechanical ball milling and spark plasma sintering. Hot compression experiments on the two materials were carried out in the temperature range of 300°C-600 °C and in the strain rate range of 0.01 s−1–10 s−1. The hot deformation activation energy of the two materials was calculated and a constitutive equation was established. The optimum hot deformation process parameters were obtained according to a hot processing map. The effects of Y 2 O 3 on the thermal deformation behavior of the Cu–10W composites and their microstructures were investigated, and the results showed that Y 2 O 3 could enhance the stability of Cu–10W at high temperatures. The activation energies of thermal deformation of Cu–10W and 2 wt%Y 2 O 3 /Cu–10W were 159.56 kJ/mol and 129.85 kJ/mol, respectively. Moreover, Y 2 O 3 improved the interfacial bonding strength of Cu and W in the Cu–10W material, effectively preventing the generation of microcracks and pores during the high-temperature compression process; Y 2 O 3 provides more nucleation sites in the recrystallization process, which is favorable for the excitation of recrystallization. A low strain rate at high temperatures favors the occurrence of recrystallization, and the 2 wt%Y 2 O 3 /Cu–10W composites tend to exhibit discontinuous dynamic recrystallization (DDRX) under high-Z-value conditions and continuous dynamic recrystallization (CDRX) under low-Z-value conditions. [ABSTRACT FROM AUTHOR]

Lightweight porous structural materials have excellent energy absorption performance, and their application are gradually appeared. This paper takes the shock-absorbing material of nuclear equipment transportation casks as the starting point, and manufactures an orthogonal trapezoidal aluminum honeycomb by welding (WOTAH). The mechanical properties with different cell thicknesses and cell size ratios under different impact loads are studied through experimental and simulation methods, and the deformation process and energy absorption performance of the materials are obtained. The energy absorption performance of materials under quasi-static loading was investigated using plastic deformation theory and compared with experimental results. Based on the experimental results, the least squares method was used for data fitting to obtain the C-S dynamic constitutive relationship of the material. The equivalent structure was used to replace the honeycomb structure for simulation, and the influence of strain rate effect and structural size on material properties was further studied. Through the above mechanical performance analysis and comparison with wood, it is shown that WOTHA has feasible for the application of nuclear equipment impact limiter. [ABSTRACT FROM AUTHOR]

The aim of this work was to develop an experimental protocol that takes into account the influence of experimental conditions on these perineal tissues, before determining their mechanical properties. Samples of each perineal tissue layer were obtained from the skin, the vagina, the external anal sphincter (EAS), the internal anal sphincter (IAS) and anal mucosa of freshly dead sows. They were tested in quasi-static uniaxial tension using the Mach-1 testing machine. Stress-strain curves of each perineal tissue layer before the first damage for each sow were obtained and modeled by hyperelastic laws described by three coefficients: C1, C2, and C3 (Yeoh model). The influence of sample preparation conditions such as tissue freezing, hygrometry and sample orientation were evaluated, and the conditions under which the tests were performed such as the displacement velocity during testing were also evaluated by analysing C1-coefficient. This study suggested that sample preparation conditions such as tissue freezing for 24 h, storage in cellophane paper for two hours and the strain rate did not statistically affect the C1-hyperelastic coefficient for each perineal layer (p > 0.05). Samples should not be stored in saline for 2 h (p < 0.05). Sample orientation did not influence C1-hyperelastic coefficient (p > 0.05). This experimental protocol could be used to study in vitro biomechanical properties of perineal tissues in order to better understand perineal tears during delivery. [ABSTRACT FROM AUTHOR]

Hot deformation behavior of the maraging stainless steel is studied in temperature range from 900 to 1150 °C and strain rate from 0.1 to 10 s−1. When the deformation temperature is 900−950 °C, the abnormal stress increase is observed at the end of the flow curves. Transmission electron micrographs reveal that the Laves phase at the interface between prior austenitic (γ) and high‐temperature ferrite (δ) impedes hot deformation. The microstructure analysis shows that the dynamic recrystallization (DRX) mechanism of γ and δ is discontinuous DRX and continuous DRX, respectively. When the specimens are deformed at 950 °C, the extent of DRX at a strain rate of 5 s−1 is higher than at 0.1 s−1. This anomaly is due to adiabatic heating causing the actual deformation temperature at high strain rate (ε.$\overset{.}{\epsilon}$) to be higher than at low ε.$\overset{.}{\epsilon}$, indicating that DRX is more influenced by temperature compared to ε.$\overset{.}{\epsilon}$. The influences of adiabatic heating and friction are corrected. Strain‐dependent constitutive equation is developed based on the revised flow curves, yielding an average absolute relative error of 4.69% and a correlation coefficient of 0.99; the prediction accuracy exceeds 90% when the relative error is within 10%. [ABSTRACT FROM AUTHOR]

Cold expansion is a mechanical method for creating residual stresses. This method is a proven technique to increase the fatigue life, and checking the residual stress on it, is of particular importance. A cold expansion process is widely used to generate beneficial residual stresses into an annular region around the hole. In the present research work, AA 6016-T6 and AA 1100 aluminum alloys which are two strain rate sensitive materials, were subjected to cold expansion process with different mandrel velocities. In fact, the effect of mandrel velocity on the created residual stresses has been investigated. The constants of the Johnson-Cook material model have been determined for them and the process has been investigated, experimentally and numerically. The obtained results revealed that the values of the residual stresses created in the sheets depend on the velocity of the process especially at the edge of the sheets holes. By increasing the mandrel velocity from 5 to 500 mm/min, depending on the distance from the hole to the edge of the sheet, it is possible to enhance the hoop residual stress by 37.3–41.2% in AA 1100 aluminum alloy and by 37.6–38.1% in AA 6016-T6 aluminum alloy. This research showed that in all cases, the radial residual stresses created around the holes are negative. Also, it was cleared that due to the existence of material constraints and the movement of the sheet material, the amount of hoop residual stress created in the mid-thickness is more than the exit face and in the exit face is also more than the entrance face, exactly unlike the size of their zones. [ABSTRACT FROM AUTHOR]

In the present article, insights into the high‐temperature deformation behavior of medium‐Mn steel (MMS), which is prepared via high‐ratio differential speed rolling (HRDSR), are provided. Moreover, through innovative bidirectional jump experiments, variations in the strain rate sensitivity index m under various conditions are obtained. In the research findings, it is indicated that an increase in strain rate (SR) leads to a hardening of the alloy. During high‐temperature deformation, the value of m decreases with the increase in SR, but the rate of decrease gradually slows down. Furthermore, the higher the temperature (T), the greater the impact of changes in SR on m. In addition, the change in deformation mechanism during deformation leads to microstructural changes, and under the main deformation mechanism of grain‐boundary sliding, m generally increases with strain. Interestingly, at a T of 760 °C, the material exhibits a strong texture with high orientation, resulting in larger m values and superior superplasticity (≈691%). This study not only enriches the research content of HRDSR but also has significant implications for the superplasticity research of MMS. Moreover, a reference is provided for the research of other superplastic materials. [ABSTRACT FROM AUTHOR]

The dynamic in-plane shear behavior of a carbon fiber/epoxy composite at different temperatures (–30, 25, 55, and 85°C) was analyzed. A split Hopkinson tensile bar system with high and low-temperature chambers was applied. The study focuses on testing ±45° symmetric carbon fiber laminated composite specimens to obtain the in-plane stress-strain curves and failure morphologies. The results revealed that the in-plane shear properties of the carbon fiber/epoxy composite are influenced by both strain rate and temperature. The stress-strain curves exhibit nonlinear characteristics at different temperatures and strain rates, with the nonlinearity becoming more pronounced as the temperature increases. Furthermore, the research indicates that in-plane shear strength and shear modulus tend to increase with higher strain rates and decrease with rising temperatures. To analyze the failure morphologies and mechanisms, scanning electron microscopy observations were conducted on the test specimens. To incorporate the effects of strain rate and temperature, the study proposes formulas for in-plane shear strength and shear modulus. The formulas proposed describe effectively the experimental data obtained. [ABSTRACT FROM AUTHOR]

The Johnson-Cook model, widely used in numerical analysis, is typically derived from split Hopkinson pressure bar tests, which are costly, time-consuming, and challenging to perform consistently. To address this, research aims to develop more efficient and consistent dynamic material models using optimization algorithms. This study employs genetic algorithm to predict key variables of the Johnson-Cook failure model for aluminum 6061, using consistent quasi-static test results as inputs. Validation was conducted through impact tests on 6 mm and 8 mm thick aluminum plates, comparing the predicted variables with impact analyses based on penetration hole diameters. The predicted variables yielded errors of 0.12 % and 2.31 % for the 6 mm and 8 mm plates, respectively, whereas reference variables showed errors of 0.40 % and 5.08 %. These findings confirm that analyses using the predicted variables more accurately simulate impact tests, demonstrating the effectiveness of combining genetic algorithms with quasi-static tests for predicting material model variables. [ABSTRACT FROM AUTHOR]

In advanced engineering applications, there has been an increasing demand for the service performance of materials under high-strain-rate conditions where a key phenomenon of adiabatic shear instability is inevitably involved. The presence of adiabatic shear instability is typically associated with large shear strains, high strain rates, and elevated temperatures. Significant plastic deformation that concentrates within a adiabatic shear band (ASB) often results in catastrophic failure, and it is necessary to avoid the occurrence of such a phenomenon in most areas. However, in certain areas, such as high-speed machining and self-sharpening projectile penetration, this phenomenon can be exploited. The thermal softening effect and microstructural softening effect are widely recognized as the foundational theories for the formation of ASB. Thus, elucidating various complex deformation mechanisms under thermomechanical coupling along with changes in temperatures in the shear instability process has become a focal point of research. This review highlights these two important aspects and examines the development of relevant theories and experimental results, identifying key challenges faced in this field of study. Furthermore, advancements in modern experimental characterization and computational technologies, which lead to a deeper understanding of the adiabatic shear instability phenomenon, have also been summarized. [ABSTRACT FROM AUTHOR]

This paper deals with Barkhausen noise in Trip steel RAK 40/70+Z1000MBO subjected to uniaxial plastic straining under variable strain rates. Barkhausen noise is investigated especially with respect to microstructure alterations expressed in terms of phase composition and dislocation density. The effects of sample heating and the corresponding Taylor–Quinney coefficient are considered as well. Barkhausen noise of the tensile test is measured in situ as well as after unloading of the samples. In this way, the contribution of external and residual stresses on Barkhausen noise can be distinguished in the direction of tensile loading, as well as in the transversal direction. It was found that the in situ-measured Barkhausen noise grows in both directions as a result of tensile stresses and the realignment of domain walls. The post situ-measured Barkhausen noise drops down in the direction of tensile load due to the high opposition of dislocation density at the expense of the growing transversal direction due to the prevailing effect of the realignment of domain walls. The temperature of the sample remarkably grows along with the increasing strain rate which corresponds with the increasing Taylor–Quinney coefficient. However, this effect plays only a minor role, and the density of the lattice imperfection expressed especially in terms of dislocation density prevails. [ABSTRACT FROM AUTHOR]

Metallization, a process for applying anti-corrosion coatings, has advantages over hot-dip galvanizing, such as reduced thermal stress and the ability to work "in situ". This process consists of the projection of a protective metal as coating from a wire as application material, and this wire is obtained by multi-stage wiredrawing. For the metallization process, a zinc–aluminum alloy wire obtained by this process is used. This industrial process requires multiple stages/dies of diameter reduction, and determining the optimal sequence is complex. Thus, this work focuses on developing models with the aim of designing and optimizing the wiredrawing process of zinc–aluminum (ZnAl) alloys, specifically ZnAl15%, used for anti-corrosion applications. Both analytical models and numerical models based on the finite element method (FEM) and implemented by computer-aided engineering (CAE) software Deform 2D/3D v.12, enabled the prediction of the drawing stress and drawing force in each drawing stage, producing values consistent with experimental measurements. Key findings include the modeling of the material behavior when ZnAl15% wires were subjected to the tensile test at different speeds, with strain rate sensitivity coefficient m = 0.0128, demonstrating that this type of alloy is especially sensitive to the strain rate. In addition, the optimal friction coefficient (µ) for the drawing process of this material was experimentally identified as µ = 0.28, the ideal drawing die angle was determined to be 2α = 10°, and the alloy's deformability limit has been established by a reduction ratio r ≤ 22.5%, which indicates good plastic deformation capacity. The experimental results confirmed that the development of the proposed models can be feasible to facilitate the design and optimization of industrial processes, improving the efficiency and quality of ZnAl15% alloy wire production. [ABSTRACT FROM AUTHOR]

Dilatancy is commonly defined as the ratio of the rates of plastic volumetric strain to plastic deviatoric strain, denoted as Dp. Owing to the high modulus of elasticity, the elastic volumetric and deviatoric strain rates under shear stress in conventional cohesionless materials are negligible. Therefore, using the ratio of the rates of total volumetric to deviatoric strain (Dt) as an approximation is common in studying stress–dilatancy behavior and calibrating dilatancy model parameters. This approach is also common in the study of rubber-added cohesionless materials (RCM). However, RCM with a common range of rubber content exhibit a significantly lower modulus of elasticity compared to conventional cohesionless materials. Further research is needed to evaluate the potential impact of elastic strain rates in RCM on stress–dilatancy analysis. Therefore, comparisons were conducted on the stress–dilatancy responses of a series of tests on RCM, where dilatancy is calculated by Dp and Dt, respectively. Furthermore, a modified method for calibrating the parameters of a state-dependent dilatancy model considering Dp is presented. It turns out that Dp is better suited and more precise for dilatancy analysis on highly elastic RCM. Additionally, the dilatancy model can more precisely capture the test results of RCM with parameters calibrated by the proposed method. [ABSTRACT FROM AUTHOR]

AA6082 alloys play a significant role in advancing sustainable development goals (SDGs) by contributing to environmental sustainability, economic growth, and social well-being. These alloys are highly recyclable and align with SDG 12 by promoting resource efficiency and reducing waste. Their application in lightweight vehicles and improving energy efficiency in construction supports SDG 9 and SDG 11, as they help reduce carbon emissions and enhance the sustainability of urban environments. While AA6082 alloys offer significant advantages, their use has limitations that can hinder their industrial applications. One key challenge is their lower formability, particularly at room temperature. Elevated-temperature deformation is frequently employed to enhance the formability of these alloys and address their limitations. Thus, a deep understanding of the constitutive analysis of these alloys under a wide range of T and ε ˙ is essential for manufacturing sound components from these alloys. Thus, this study aims to propose a new modification for the JC model (PJCM) and compare its reliability to predict the warm/hot flow behavior of AA6082 alloys with that of the original JC model (OJCM) and the modified JC model (LMJCM). By comparing the experimental results with these model results and confirming the determining correlation coefficient (R), average absolute relative error (AARE), and root mean square error (RMSE) values, it is concluded that the stresses predicted by the PMJCM closely match the experimental stresses of the LMJCM and OJCM because of the interaction between ε ˙ , ε , and T , which might be a reason for the complex nonlinear behavior of AA6082 alloys during hot deformation. [ABSTRACT FROM AUTHOR]

Owing to their excellent properties, duplex stainless steels (DSSs) may be selected for the H2S environment. Operational limits are not defined and depend on fabrication processes. In this work, the susceptibilities of two DSSs 2205 to sulfide stress corrosion (SSC) in saline solutions with three pH levels were investigated. The difference between materials is the fabrication route: hot rolled (HR) tubes and powder metallurgy with compacting and sintering final operations by hot isostatic pressing (PM‐HIP). The susceptibility parameters were evaluated by slow strain rate tensile tests (SSRT). Both materials suffered embrittlement in solutions with pH 3.5 and 4.5, but the susceptibility was slightly better in the HR. In the solution with pH 5.5, the HR fractured with ductile behavior, while the PM‐HIP was brittle. The better resistance of HR to SSC can be explained by microstructural features, such as the lower grain size and austenite island interspace. [ABSTRACT FROM AUTHOR]

In this work, the effects of Nb micro-alloying on the stress corrosion cracking (SCC) behaviors of the heat-affected zone (HAZ) of high-strength low-alloy (HSLA) steel exposed to SO2-polluted seawater were investigated using electrochemical measurements, static load U-bend immersion tests and slow strain rate tensile experiments combined with fractographic observations. Results indicated that Nb existed in solute status in the coarse-grained HAZ (CGHAZ) while simultaneously in the form of solute status and NbC precipitate in the fine-grained HAZ (FGHAZ) and inter-critical HAZ (ICHAZ). With reduced prior austenite grain sizes, Nb micro-alloying refined the lath bainite in the CGHAZ as well as induced the formation of acicular ferrite in the FGHAZ and granular bainite in the ICHAZ. Moreover, the three types of HAZ microstructures had a high SCC susceptibility in SO2-polluted seawater in the increasing order of ICHAZ < FGHAZ < CGHAZ under the combined mechanism of anodic dissolution and hydrogen embrittlement. Nevertheless, attributing to the variations of microstructural constituents and the presence of NbC precipitates, Nb micro-alloying was capable to enhance the SCC resistance of HAZ microstructures by inhibiting the initiation and propagation of SCC cracks, with the SCC susceptibility decreased by ~ 5%, ~ 28% and 24% for CGHAZ, FGHAZ and ICHAZ, respectively. [ABSTRACT FROM AUTHOR]

In multiple physical fields, the mutual influence among these fields can significantly impact material elastoplasticity. This paper proposes a thermodynamic-based constitutive model that incorporates the mutual influence of multiple physical fields. Rather than treating physical field characteristics as adjustable "parameters" affecting material coefficients, the proposed model employs a thermodynamic dissipation potential derived from the Onsager reciprocity relations, accounting for thermodynamic forces coupling. This dissipation potential ensures that the thermodynamic flow in the stress field is influenced by both stress field and other physical fields thermodynamic forces, which describes the plastic flow under multiple physical fields, while preserving thermodynamic duality. The paper begins with the formulation of a generalized thermodynamic model applicable to diverse materials and types of coupled fields, which is then degraded to a specific model for AA5182-O AlMg alloy under the influence of temperature and strain rate fields coupling. Given the universal applicability of the generalized model, such degradation provides a structured approach framework for developing thermodynamics-based constitutive models. For different materials encountered in practical engineering, new thermodynamic forces can be introduced to describe their unique mechanical properties while preserving the overarching thermodynamics-based model framework, thereby facilitating model scalability. The paper concludes with a validation example, showing that within the Portevin-Le Chatelie (PLC) regime, the plastic flow stress of AA5182-O AlMg alloy decreases with increasing strain rate at low temperatures but increases at high temperatures. The accurate simulation of these distinct strain rate effects crucially relies on integrating the mutual influence of temperature field and strain rate field. [ABSTRACT FROM AUTHOR]

As one of the hotspots in rock mechanics research, coal rock's dynamic tensile properties are crucial to the parameter selection of blasting engineering, mechanism studies of rock burst disasters, and stability control. The stress states of coal rock during indirect tension with Brazilian splitting and direct tension with split Hopkinson tensile bar (SHTB) were compared using numerical simulations, revealing the superiority of the direct-tension test. On this basis, systematic dynamic direct-tension tests of coal rock under the strain rates (124 to 247 s−1) were carried out utilizing the improved SHTB, and quasi-static tensile tests were performed for comparison. The results reveal that the connection mode of using high-strength adhesive paste specimens and gradient reinforcement with steel wire mesh is reliable for SHTB tests. However, the stress equilibrium is no longer satisfied if the strain rate exceeds 300 s−1, and the layered fracture of the specimen will occur. With an increase in strain rate, the dynamic elastic modulus increases linearly, the dynamic tensile strength tends to increase as an exponential function, and the dynamic increase factor (DIF) tends to increase linearly in two stages. The DIF grows slowly once the strain rate is over 180 s−1 and the dynamic ultimate tensile strength of the coal rock lies around 8 MPa. Finally, based on the improved Zhu–Wang–Tang (ZWT) model and the introduction of dynamic damage factor, the unified damage constitutive equation that can describe the strain rate effect under dynamic tension of coal rock is constructed. Moreover, the rationality of the constitutive parameter value is verified. Highlights: Superiority of direct tension test over Brazilian disk tensile test is revealed Functional relationship between tensile DIF and strain rate of coal rock isobtained Unified damage constitutive model of coal rock under dynamic tension isconstructed [ABSTRACT FROM AUTHOR]

The long-term stability and safety of underground engineering greatly depend on a thorough understanding of the creep characteristics of fractured rock. This paper discusses the potential application of the damage evolution equation and the fractional derivative operator for describing the creep characteristics of fractured rock. By considering the initial damage of the original fracture and the internal damage induced by external loads, coupled damage evolution equations are proposed to account for different failure mechanisms. The introduction of damage and fractional calculus into basic mechanical elements allows for the deduction of creep constitutive relationships for both viscoelastic and viscoplastic bodies. A range of fractional-order damaged creep models is developed based on the Burgers model and the Nishihara model. Parameter sensitivity analysis shows that the inclusion of the damage evolution equation in the creep model is crucial for accurately capturing the accelerated creep deformation characteristics of rock, with the fractional derivative order primarily affecting the steady creep strain rate. By fitting the creep experimental data of fractured Beishan granite, it is evident that the damaged Nishihara model [H-N(D)/H(D)-N(D)/St. V model], which considers only the damage effect, and the fractional damaged Burgers model [H-N(A)-N(D)/H(D) model], which accounts for both the damage effect and the fractional operator, exhibit significant advantages in characterizing the entire process of creep deformation in fractured granite. Highlights: Coupled damage evolution equations for fractured rock with different inclination angles are proposed to account for different failure mechanisms. Fractional order damaged creep models are developed by incorporating damage equations and fractional calculus into basic mechanical elements. The inclusion of the damage in the creep model is crucial for capturing the accelerated creep deformation characteristics of the rock. The fractional derivative order mainly affects the steady state creep strain rate. The validity and applicability of the model are verified by fitting the experimental data of fractured granite. [ABSTRACT FROM AUTHOR]

Pure titanium due to its high corrosion resistance, low stiffness and good mechanical properties is commonly used in medicine for orthopaedic applications. However, its material properties (especially in the case of α -titanium) require a further enhancement to fulfil its role. The thermoplastic deformation in mid-temperature is proposed as a method for microstructure improvement. Titanium samples were compressed in different temperatures and strain rates to determine the best conditions for grain fragmentation—the main factor responsible for strength and hardness increase. The thermoplastic stress–strain curves were registered. Then microstructure observations and electron backscatter analysis were performed on the chosen samples. Finally, mechanical response of the previously deformed material was obtained in room temperature compression tests. A significant grain fragmentation was recorded for the material deformed in 400 ∘ C , at 0.1/s and 1/s strain rates. Desirable results were also noticed for the deformation performed at 500–600 ∘ C . However, high temperatures (700–800 ∘ C ) and strain rates (10/s) resulted in dynamic recrystallization, causing undesirable grain growth. An increase in hardness was observed in all cases, with higher values recorded in lower deformation temperatures. Room temperature compression tests revealed slight increase of ductility. [ABSTRACT FROM AUTHOR]

In this study, we address the challenge of hidden damages in FRP composites, such as delamination, matrix cracking, and fibre breakage resulting from transverse low-velocity impact (LVI)—damages often elusive on the surface. Our methodology operates at the meso-scale, depicting laminates as stacked homogenized plies incorporating interfaces. To capture the mechanical behaviour and damages, we extend an existing nonlinear mean-field debonding model (NMFDM), accommodating asymmetric matrix plasticity (AAMP), fibre–matrix interface debonding failure, and in-plane progressive failure. In a key enhancement, we introduce a strain rate term to the AAMP model, addressing strain rate effects associated with LVI loading. Additionally, we incorporate a novel strain-driven 3D failure criteria, offering a more precise assessment of progressive failure subjected to LVI loading. The interfaces between plies are modelled using surface-based cohesive behaviour to capture interaction phenomena. To validate the developed NMFDM, we conduct impact simulations at various energies on a UD composite laminate consisting of AS4/8552 carbon fibre and epoxy matrix. These simulations showcase the predictive capability and accuracy of the NMFDM in capturing the intricate behaviour and damage progression of UD composites subjected to LVI. [ABSTRACT FROM AUTHOR]

To what extent mechanical anisotropy is required to explain the dynamics of the lithosphere is an important yet unresolved question. If anisotropy affects stress and deformation, and hence processes such as fault loading, how can we quantify its role from observations? Here, we derive analytical solutions and build a theoretical framework to explore how a shear zone with linear anisotropic viscosity can lead to deviatoric stress heterogeneity, strain-rate enhancement, as well as non-coaxial principal stress and strain rate. We develop an open-source finite-element software based on FEniCS for more complicated scenarios in both 2-D and 3-D. Mechanics of shear zones with transversely isotropic and orthorhombic anisotropy subjected to misoriented shortening and simple shearing are explored. A simple regional example for potential non-coaxiality for the Leech River Schist above the Cascadia subduction zone is presented. Our findings and these tools may help to better understand, detect and evaluate mechanical anisotropy in natural settings, with potential implications including the transfer of lithospheric stress and deformation through fault loading. [ABSTRACT FROM AUTHOR]

This paper presents the stress–strain behaviour of three structured clays subjected to a number of stepwise changes in strain rate during shearing in a triaxial apparatus. Undrained compression tests were performed on clay specimens in both undisturbed and reconstituted states. As a result, it has been possible to identify the influence of structure on the rate-dependent response of the clays. Step changes in applied shearing strain rates for all tests resulted in predominately isotache-type behaviour within the range of strains from very small strains to large strains at failure. At very small strains, evidence of a limiting elastic modulus was established for both the stiff sedimentary and artificially cemented soil, which is consistent with published literature on other structured geomaterials. The stress–strain behaviour of all three materials was affected by both the degradation of structure with increasing strain and applied strain rate. The influence of structure on the time-dependent behaviour of the clays is discussed by comparing the response of undisturbed and reconstituted specimens and following normalisation by the equivalent pressure. Results indicate that the rate sensitivity evolves with increasing strains and reaches a maximum at strain levels associated with peak shearing resistance. [ABSTRACT FROM AUTHOR]

Rocks often have a rate effect on mechanical behaviors and exhibit a negative Poisson's ratio (NPR) effect after being thermally damaged. However, to date, their combined role in mechanical behaviors has not been clarified. This study micromechanically explores the rate and NPR effects on the compressive behaviors of thermal-damaged rocks using the compression-hardening grain-based model (CHGBM) implemented by the Universal Discrete Element Code (UDEC). The original, moderately, and highly thermal-damaged Suizhou granite samples were subjected to unconfined compression tests for calibrating UDEC-CHGBM. With developing thermal damage from the original state, the rock sample decreases in the peak stress and modulus, exhibiting a transition of pre-peak stress-stain relation from the approximately linear to nonlinear, and a transition of Poisson's ratio from the positive (lateral extension) to negative (lateral contraction). Our UDEC-CHGBM reproduced these experimental phenomena with reasonable accuracy. With increasing strain rates, the peak stress and modulus increase in a power law manner. The dynamic increase factors of the peak stress and modulus also increase with enhancing thermal-damaged degrees. Due to the thermal damage, the grain contact increased in the maximum allowable closure, thus enhancing compression-hardening capacity and nonlinear characteristics, resulting in a promotion of the rate effect. Lateral contraction deformation can reduce the proportion and magnitude of the tensile stress within the sample, and inhibit intergranular microcracking. The NPR effect depends on both the degree of thermal damage and strain rate. We shed light on the synergistic effects of the rate and NPR on macro- to micromechanical behaviors of thermal-damaged rocks. [ABSTRACT FROM AUTHOR]

A three-dimensional viscoelastic-viscoplastic constitutive model is presented for predicting the dynamic mechanical behavior of an epoxy resin at low-to-medium strain rates. The model utilizes the generalized Maxwell model, incorporating two Maxwell elements in parallel with a nonlinear spring to represent the viscoelastic response at low and medium strain rates. By utilizing an empirical logarithmic relationship to predict the material properties at different strain rates, a nonlinear exponential relation based on overstress concepts is proposed for modeling the viscoplastic behavior. Comparing the tensile and shear stress–strain curves predicted by the proposed model with the experimentally measured curves, a good agreement is observed. Implementing the viscoelastic-viscoplastic model in commercial finite element software, a three-dimensional numerical discretization is performed. Through simulations of stress-relaxation and loading–unloading tests at various strain rates using the proposed material model, relaxation and hysteresis responses are analyzed. The model successfully predicts the experimentally measured hysteresis response of a specific epoxy resin during the loading cycle, consistent with other nonlinear viscoelastic models. This material model not only well replicates the nonlinear viscoelastic responses below the yield strain but also captures plastic nonlinearities at different strain rates. [ABSTRACT FROM AUTHOR]

Conventional sheet metal forming processes have problems like low formability, non-uniform strain distribution, spring back, wrinkling, etc. High velocity processes like electrohydraulic forming can deform sheets at high strain rate and have capability to tackle such problems associated with conventional forming operations to a greater extent. Forming limit diagram (FLD) characterizes sheet deformation as measure of formability. Punch stretch test (PST) can assess formability of sheet in conventional low strain rate process, but no standard method is available to determine FLD at high strain rate. So in the present work, an experimental setup has been developed to characterize sheets at high strain rate using hydraulic forming process with a 40 kJ capacitor bank. A similar corresponding standard setup for punch stretch test is also developed for comparative study of formability with respect to dome height, forming limit curve, and strain distribution. Formability of aluminum alloy AA5754 is determined at quasi-static and high strain rates, and comparative analysis is reported for whole state of strain using dog bone samples of width ranging from 10 to 120 mm. An estimate of electrohydraulic forming parameters for high strain test of the Al alloy using the given setup is also determined. Study of comparative strain distribution behavior of samples of different widths is also carried out. Comparative analysis shows that there is an improvement in formability and strain distribution behavior of the alloy deformed using EHF as compared to PST. [ABSTRACT FROM AUTHOR]

Iron tailing porous concrete (ITPC) is a type of foamed concrete material that uses iron ore tailings powder to partially replace cement. As a relatively new concrete-like material, only very limited research on the dynamic material property of ITPC under high strain rates has been performed. To supplement the material properties for its practical applications, in this study, splitting Hopkinson pressure bar (SHPB) tests were carried out to measure the dynamic properties of ITPC specimens with a density range of 600 kg/m3–1,200 kg/m3 in a strain rate range of about 120 s−1–250 s−1. The influences of strain rate and density on the impact resistance performance of ITPC were analyzed based on the failure modes, stress–strain relations, compressive strengths, elastic moduli, peak strains, and dynamic increase factors (DIFs). The microstructures of ITPC after impact were also observed and characterized by scanning electron microscopy (SEM). Moreover, the energy dissipation characteristics were discussed and analyzed. The test results indicate that the dynamic properties of ITPC exhibit significant strain rate effects and density dependence. The dynamic compressive strength of ITPC increases quadratically and linearly with density and strain rate, respectively. Moreover, the empirical formulas for dynamic compressive strength, DIF, energy dissipation ratio, and energy dissipation capacity of ITPC as functions of strain rate and material density are proposed based on the experimental data; the variation trends of these key dynamic mechanical parameters of ITPC are analyzed and discussed in detail. [ABSTRACT FROM AUTHOR]

This investigation delves into the impact of temperature and tensile strain rate on the mechanical characteristics of high-strength Q960 steel. The inherent strength and stiffness properties of steel undergo degradation as temperatures rise, necessitating meticulous consideration in the fire-resistant structural design of steel constructions. Meanwhile, tensile strain rate will influence the mechanical properties of the steel at high temperature. Due to the absence of data specifically tailored to high-strength Q960 steel, design standards assume its high-temperature strength variation is equivalent to that of conventional mild steel. To fill this knowledge gap, tensile tests were conducted on Q960 standard specimens in the temperature range of 25°C–800°C, using three different tensile strain rates: 0.001/min ; 0.02/min ; and 0.2/min. In accordance with the stress-strain curves, mechanical properties parameters and corresponding reduction factors of the steel were obtained. The test outcomes were contrasted with those of other high-strength steel specimens. This comparison shows that the rate of strength and stiffness loss with temperature increases with increasing steel grade. The test results were also compared with the mechanical properties suggested in pertinent design codes or standards. A new predictive formula has been introduced specifically for the assessment of material properties of Q960 steel in high-temperature environments. [ABSTRACT FROM AUTHOR]

Concrete structures, such as armories, military bunkers, and petrochemical facilities, are susceptible to explosive loads during service. The superior mechanical properties of ultrahigh-performance concrete enable structures built with it to endure explosive loads. This study aims to characterize the behavior of ultrahigh-performance concrete at different ages, namely, 1, 3, 7, 14, and 28 days, at different strain rates. The compressive stress–strain response of ultrahigh-performance concrete is studied at static and high-strain-rate loading. The high-strain-rate response is characterized using a split-Hopkinson pressure bar of 100-mm diameter. The influence of age on strength, dynamic increase factor strain rate, elastic modulus, peak strain, and energy absorption are discussed. When tested at the same striker velocity, the dynamic increase factor and strain rate of ultrahigh-performance concrete of similar specimen size decrease with age. The elastic modulus and energy absorption increase from 1 to 14 days. There is no significant change in these quantities between 14 and 28 days. The strength, elastic modulus, and energy absorption increase with increasing strain rate for all ages. Experimental data are validated using the Tedesco model and current standards for stress, strain, and elastic modulus. The model from the standards overestimates strength, whereas the Tedesco model predicts strength conservatively. [ABSTRACT FROM AUTHOR]