High Strain Rate Research Articles

Optimization of Mechanical Machining for Heat-Resistance Ta-W Alloy by Using Orthogonal Cutting Method

Tantalum and tantalum alloys, which have superior thermal properties, including a high melting temperature, low specific heat, low thermal conductivity, and high density, are promising candidates for highperformance parts exposed to high temperatures and hazardous environments in aerospace, defense, and other industries. However, those alloys are hard to cut and mechanically machine, and the poor machinability of tantalum alloys has precluded their wide use. This study investigates mechanisms for cutting Ta-10%W alloys using orthogonal cutting methods for precision part manufacturing. During orthogonal cutting processes, the cutting forces are increased dramatically because of the surface folding phenomenon of Ta-W alloys. As a result of experiments and simulation calculations, the tool’s rake angle and depth of cut are critical parameters for controlling the cutting shear angle, which makes a significant difference in chip thicknesses and surface folding phenomenon. Based on the results, about 12 degrees of cutting shear angle is suitable for the mechanical machining of a Ta-W alloy. Additionally, cutting speed may be one of the critical parameters to consider for changing the mechanical responses of Ta-W alloys. With this perspective, the mechanical properties of Ta-W alloys at high strain rates seem to be an important factor in orthogonal cutting. Based on these results, the cutting mechanisms and optimal cutting parameters for Ta-W alloys are discussed.

Variation law of micro-void distribution characteristics in early stage of spallation damage

The development trend of spallation damage mechanics is to construct a physical model that couples information with micro-mesoscale structure of materials, which also promotes the development of numerical calculation methods, experimental techniques and theoretical research. The mechanism responsible for plastic deformation and failure of structural metal materials at high strain rates is complex and ainfluenced by heterogeneities in the micro-mesoscale structure that comprises the distribution of grain boundaries, interfaces, and pre-existing densities voids. The distribution of these mesoscale heterogeneities can provide either strengthening behavior or void nucleation sites and influence spall failure behavior. Due to the lack of evolutionary information of micro-mesoscopic void distribution characteristics, the current spallation damage model is not only restricted in its application in extreme environments with high strain rates, high pressures, and shock, but also does not effectively provide some information about the correlation between material damage and final material fragmentation particle size, which is of very concern in engineering. Therefore, it is urgent to develop a spallation damage model that can reflect the variation law of micro-mesoscopic void distribution characteristics in damaged materials. The probability distribution function of void nucleation based on cosine function is given in this work by analyzing various influencing factors in the process of void nucleation, combining the characteristics of early void growth, and considering the convenience of analytical solution. The analytical calculation results of the new probability function of void nucleation are consistent not only with the results of the variation of void number with time calculated by molecular dynamics, but also with the experimental results of tantalum spallation in the early stage of damage development, that is to say, the new probability function of void nucleation can reflect the variation law of micro-void distribution characteristics in the early stage of spallation damage to a certain extent.

Strain hysteresis and Mullins effect of rubber vulcanizates with a reversible sacrificial network.

The incorporation of reversible sacrificial bonds is an important strategy for enhancing the mechanical properties of elastomers. However, the research on the viscoelasticity of vulcanized rubber with a reversible sacrificial bond network lags seriously. In this paper, the effects of metal coordination bonds on the mechanical properties of butadiene-styrene-vinylpyridine rubber vulcanizates (VPR) were systematically investigated. The experimental results showed that lower temperature and higher strain rate under smaller strain were advantageous in reflecting the significant contribution of sacrificial bonding. Compared with the conventional rubber nanocomposites, the sacrificial bond enhanced the energy dissipation while also improving reversible hysteresis energy and its proportion, revealing the origin of better self-healing and damping properties. The high-temperature rearrangement of sacrificial bonds promoted not only the recovery of mechanical properties, but also the recovery of covalent networks. The evolution mechanism of the network structure and viscoelasticity research under different thermal-mechanical coupling conditions could help to control the rubber network structure, providing a promising method for the regulation of the nonlinear behavior of rubber composites.

“Rigid-flexible” dynamic polymers based on borate bonds

Strain-dependent materials, such as non-Newtonian fluids and "solid-liquid" dynamic polymers, are soft in the normal state and exhibit significant stiffness only at higher strain rates. No material has been reported...

Directed energy deposition (DED) of Inconel 718-SS316L bimetallic structures: Experimental investigations and optimization through artificial humming bird algorithm for improved high strain rate and mechanical properties

Directed energy deposition (DED) of Inconel 718-SS316L bimetallic structures: Experimental investigations and optimization through artificial humming bird algorithm for improved high strain rate and mechanical properties

Deformation mechanism and microstructure evolution of newly developed Ti-42.5Al-4Nb-0.5Mo-0.1B-(C, W, Y) alloy

A novel Ti-42.5Al-0.5Mo-0.1B-0.2W-0.25C-0.05Y alloy with a nearly lamellar structure was explored to better understand the deformation behavior and microstructure evolution during hot compression test at a high strain rate of 10s-1. Cylindrical samples were compressed in the temperature range of 1373K to 1523K, with the true strain reaching 69%. The results show that the crystal structure and phase transformation have an influence on the deformation mechanisms. Regarding the Tα2→α transformation within the deformation temperature range of 1373K - 1473K, the nucleation and growth of dynamically recrystallized (DRXed) γ and α grains can alternate in dominating the hot deformation of the present alloy. When the deformation temperature is 1523K, the softening mechanism mainly is the dynamic recovery (DRV) of the α phase. Moreover, the deformation temperature also has a significant effect on phase fractions and the critical values of dynamic recrystallization. Specifically, as the temperature rises, the proportion of the α phase increases, the proportion of the γ phase decreases sharply, the content of the β phase remains stable, and the critical values of dynamic recrystallization decrease. Additionally, fine equiaxed α2 grains with an average size of 8 μm were obtained at 1523K and 10s-1, which provided a reference for obtaining a fine near-lamellar or full-lamellar microstructure in TiAl alloys.

Microstructure evolution and dynamic recrystallization mechanism of tantalum-tungsten alloys under hot compression

Ta-W alloys exhibit outstanding comprehensive properties at high temperatures, allowing them to have great application prospects in the high-temperature field. High-temperature compression tests (1573~1873 K) were conducted to evaluate the high-temperature mechanical properties of Ta-12W alloy, and the strain-compensated Arrhenius-Type model and hot processing map were developed to predict the optimal processing window. The electron backscatter diffraction, Transmission electron microscope, and DEFORM-3D software were performed to investigate the microstructure evolution and distributions of strain. The results demonstrated that the flow stress of Ta-12W alloy presented apparent negative temperature sensitivity and positive strain rate sensitivity. Based on the thermal processing diagrams and EBSD analysis, the results show that the low deformation temperature and high strain rate introduce stress concentration and deformation instability in the Ta-12W alloy. The optimized processing temperature and strain rate are at 1800 ~1873 K/0.001 s-1~0.05 s-1, and the microstructure at 1873 K/0.001 s-1 is more uniform and exhibits a low residual stress level. As the temperature increases, dynamic recovery and dynamic recrystallization cause significant softening effects, and continuous dynamic recrystallization dominates the high-temperature deformation behavior. Moreover, multiple continuous dynamic recrystallizations occur simultaneously, including sub-grain nucleation inside large grains, sub-grain nucleation at grain boundaries, and grain fragmentation accompanied by grain rotation. This study revealed the mechanisms of microstructural evolution during hot deformation of Ta-12W alloy, providing important guidance for optimizing the thermomechanical processing parameters.

The Effect of Sub-Zero Temperature and High Strain Rate on Mechanical Strength of 9/7 ‘Oak’ Gun Propellant

The Effect of Sub-Zero Temperature and High Strain Rate on Mechanical Strength of 9/7 ‘Oak’ Gun Propellant

Measurement of Dynamic Mechanical Property Parameters of 12X18H10T at High Strain Rates

To measure the dynamic mechanical properties of 12X18H10T stainless steel at high strain rates, dynamic impact tests were conducted on 12X18H10T specimens at three high strain rates using the SHPB apparatus. The dynamic engineering stress-strain data and true stress-strain data of 12X18H10T stainless steel at different strain rates were obtained using the classical three-wave method theory. The engineering stress-strain data and the Cowper-Symonds constitutive model were used to fit least squares data to obtain the dynamic yield strength and strain rate-dependent parameters separately. This provides input data for the drop test simulation of shipping containers of radioactive materials considering the strain rate effect.

Static Properties of Kaolinite Samples from Different Structures and the Influence of Strain Rate

This paper conducts triaxial undrained tests on flocculated and dispersed kaolin samples at strain rate range 0.005–1%/min to investigate the effects of structure and strain rate on shear strength. The test results show that the flocculated samples exhibit strain hardening behaviour, while the dispersed samples show strain softening behaviour. The strain rate sensitivity parameter reflects the degree to which shear strength increases with increasing strain rate. The structure affects the strain rate sensitivity parameter, with values of 4.79% and 2.31% for flocculated and dispersed samples, respectively. When the strain rate is 1%/min, due to the low permeability of the dispersed sample, the high strain rate causes a rapid increase in local pore pressure, while the postponed dissipation of excess pore pressure destroys the sample. When studying the influence of clay structure, it is important to use the same strain rate; otherwise, the differences in shear strength may be underestimated.

Tensile Properties, Strain Rate Sensitivity and Microstructural Analysis of SN100C Solder Alloys

Sn-Cu-Ni-Ge (SN100C®) is a high-performance Pb-free solder alloy widely used in the electronics manufacturing industry due to its excellent soldering performance and lower cost. SN100C has a huge potential to replace the commonly used Sn-Ag-Cu solders. This work investigates the effect of different strain rates (10-3 to 8×10-1s-1) on tensile performance for bulk SN100C samples at room temperature. The tensile properties, e.g., elastic modulus (E), yield strength (σy) and tensile strength (σT) are determined from the stress-stress curves. The value of σy and σT increases with increasing strain rates and this increase becomes less prominent at higher strain rates. Necking and ductile fracture are observed for all samples with a significant number of dimples, voids and tongues formed. The level of ductility of the samples decreases with increasing strain rates, which is further confirmed by the stress-strain behaviour. The microstructural evolution of the samples is evaluated by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) to reveal the generation of recrystallisation and fracture of the intermetallic compounds (IMCs) at the fracture tips and identify the embedded of IMCs within the sample matrix.

Cardiac Magnetic Resonance Imaging with Myocardial Strain Assessment Correlates with Cardiopulmonary Exercise Testing in Patients with Pectus Excavatum.

Objectives: To evaluate correlations between cardiac magnetic resonance imaging (cMRI) at rest including strain imaging and variables derived from quantitative cardiopulmonary exercise testing using a treadmill in patients with pectus excavatum. Methods: We retrospectively correlated the results of cMRI and cardiopulmonary exercise testing in 17 patients with pectus excavatum, in whom both examinations were performed during their pre-operative clinical evaluation. In addition to cardiac volumetry, we assessed the strain rates of both ventricles using a feature-tracking algorithm of a piece of commercially available post-processing software. Results: Right ventricular (RV) ejection fraction correlated negatively with heart rate at anaerobic threshold (rho = -0.543, p = 0.024). A positive correlation between radial strain rate at the RV base and percentage of predicted maximum heart rate (rho = 0.72, p = 0.001) was shown, with equivalent results for circumferential strain rate (rho = -0.64, p = 0.005). Radial strain rate at the RV base correlated in a strongly negative way with maximum oxygen uptake (rho = -0.8, p < 0.001), with a correspondingly positive correlation for circumferential strain rate (rho = 0.73, p = 0.001). Conclusions: Quantitative parameters derived from cMRI at rest, especially those acquired at the most severely compressed RV base, correlated with cardiopulmonary exercise testing variables. The compression of the RV base by the sternum might be partially compensated by an increased strain rate to induce higher heart frequencies during exercise. However, high strain rates were associated with a higher disease severity and a lower maximum oxygen uptake, indicating a limitation of this compensation mechanism.

The tensile behaviour of paper under high loading rates

AbstractThis work deals with the strain-rate dependent characterization of paper under uniaxial tension at high strain-rates. Experiments were performed involving a Split Hopkinson bar for high strain-rate testing, comparing the results with conventional quasi-static tests. Tests were conducted in a strain-rate range between 0.0083 and 212 s−1, which is equivalent to testing velocities between 0.0003 and roughly 13.6 m/s. For the first time the change in tensile behaviour of paper is comprehensively characterized and modelled, using the Cowper-Symonds model for strain-rate hardening. The experimental tests showed that the tensile strength as well as the initial stiffness were gradually increasing with increasing strain-rate. The increase in tensile strength between the lowest and the highest strain-rate was 58% on average whereas the mean increase in stiffness between these two strain-rates was almost 115%. Regarding the fracture strain, it was observed that it significantly decreases with increasing strain-rate. While the average fracture strain of the quasi-static tests was at roughly 6% it was close to 3% for the dynamic tests. In case of the Split Hopkinson bar tests, high-speed videos of the samples were made to determine their elongation via target tracking and digital image correlation (DIC). We found that strain localization, which is a highly relevant mechanism for quasi-static tensile failure, is likely related to short term plastic creep of the material as strain localization nearly entirely disappears at high loading rates of paper.

The mechanical behavior and deformation mode of multilayer composite structures based on triply periodic minimal surface elements

In this paper, the mechanical behavior and compression deformation mode of three types of composite multilayer structures based on triply periodic minimal surfaces (TPMS) were conducted through experiments and finite element analysis. The results indicate that the load-displacement curves under varying stain rates manifest a double-platform characteristic for all three structure types. The P-G four-layer structure and P-G six-layer structure have no discernible extrusion of the structural layers during compression, and the entirety of the structure displays an almost regular cubic configuration after compression. Nevertheless, local separation was observed in the extruded portion of the P-H six-layer structure after the structural deformation at higher strain rates. For the other conditions, the structure exhibited a bulge but did not display any local detachment or separation phenomena. During the deformation of the P-H six-layer structure, a dome-shaped region emerges in the first and fifth layers. The “crown” layer displays an inverted bell-shaped failure mode for the first layer structure, exhibiting downward extrusion. In contrast, the fifth layer structure displays an upward extrusion and exhibits a bell-shaped failure mode. The P-H 6-layer structure has the best energy absorption performance under quasistatic compression conditions for the P-G 4-layer, P-G 6-layer and P-H 6-layer structure. However, the energy absorption performance of the identical structure remains largely consistent across varying strain rate conditions.

Dynamic compressive properties and constitutive model of waste crumb rubber (CR) modified ultra-high performance engineered cementitious composites (UHP-ECC)

Ultra-high-performance engineered cementitious composites (UHP-ECC) are well-known for their outstanding mechanical properties under static and dynamic loads. However, the effect of modifying UHP-ECC with crumb rubber (CR) on its performance, especially under high strain rates, remains poorly understood. This study systematically examined the dynamic compressive behavior and characteristic failure patterns of CR-modified UHP-ECC under high strain rates using a split Hopkinson pressure bar (SHPB) system. The study focused on evaluating the dynamic compressive strength, stress-strain response, and strain energy density (SED). A dynamic increase factor (DIF) formula was developed based on experimental data, and a nonlinear viscoelastic constitutive model was proposed to predict compressive behavior across various strain rates. Results indicate that while the addition of 10% CR slightly reduces the quasi-static compressive and flexural strength, it significantly enhances tensile ductility. Under high strain rates, CR-modified UHP-ECC shows no substantial effect on peak compressive stress but a marked increase in peak compressive strain. The SED also increased by 20.2%, outperforming other high-performance materials such as UHPC and normal ECC. These findings demonstrate that incorporating 10% CR into UHP-ECC offers considerable advantages, particularly in enhancing structural resilience under dynamic loading conditions. The proposed nonlinear viscoelastic model accurately predicts the compressive behavior of CR-modified UHP-ECC, presenting significant implications for practical engineering applications where high strain rate performance is crucial.

Design of a novel high-speed tensile method for testing the high strain rate tensile behavior of aluminum alloys.

The high-strain rate mechanical behavior of aluminum alloys is crucial for the stability of electromagnetic launch systems. However, current high-strain rate testing methods are not suitable for large-scale screening of materials needed in electromagnetic launch systems due to their low precision and high cost. In this paper, a novel method for high-strain rate tensile testing of aluminum alloys based on magnetic pulse driving was proposed. The method can generate a fast-rising edge and adjustable stress pulses to enable uniaxial tensile deformation, reaching a target strain rate quickly and keeping it constant. Based on the theory of stress wave transmission, a single-point method for measuring stress-strain relationship of the specimen combining digital image correlation (DIC) technology is proposed. Finite element simulations using the explicit finite element software LS-DYNA demonstrate a good agreement between the strains and strain rate with experimental values. Tensile tests were conducted on AA7075 in the strain rate range of 1000-3000s-1, the stress-strain relationship obtained from DIC agrees well with the results of traditional Hopkinson bar experiments.

Mechanical Responses and Deformation Mechanisms of Low-Cost High-Entropy Alloy AlCrFe2Ni2 with Heterogeneous Structure Subjected to High-Strain Rate Deformation

Introducing heterogeneous structures into metallic materials through composition design is a promising strategy for simultaneously improving the strength and ductility of the materials. In this work, a novel dual-phase low-cost AlCrFe2Ni2 high-entropy alloy (HEA) was designed and prepared. Its phase constitution, microstructure, dynamic mechanical responses at strain rates ranging from 1100[Formula: see text]s[Formula: see text] to 4800[Formula: see text]s[Formula: see text] as well as deformation mechanisms were investigated. It was found that the HEA consists of FCC, B2 and BCC phases and has a heterogeneous microstructure containing dual-phase alternate lamellar and high-density precipitates. The HEA displays the optimal mechanical properties at the strain rate of 4800[Formula: see text]s[Formula: see text], of which the yield strength, maximum flow stress and strain are 1222.9[Formula: see text]MPa, 2340.8[Formula: see text]MPa and 30.5[Formula: see text]%, respectively, better than that of most single-phase FCC or BCC HEAs, dual-phase HEAs and traditional alloys. The deformation mechanism of the HEA at the strain rate of 4800[Formula: see text]s[Formula: see text] involves both dislocation slip and deformation twinning, with the former dominating. This work could provide guidance and insights for designing metallic materials with excellent mechanical properties at high strain rates.

Effect of the flow behavior and dynamic recrystallization of EH420 marine steel on the morphology evolution of martensite substructures

The hot deformation behavior of EH420 marine steel was investigated by isothermal compression tests in the temperature range of 850~1050°C and the strain rate range of 0.01~10s−1. A high-temperature constitutive model and a hot processing map were developed. The results indicated that the microstructure of EH420 marine steel after hot deformation was mainly bainite and lath martensite. The martensite blocks gradually coarsened with the increase in temperature within the range of 950~1050°C/0.01s-1, and the average width increased from about 0.7 μm to 2.3 μm. At high strain rates, martensite blocks became coarse and disordered due to flow instability. The flow stress curve showed a single peak when the strain rate was low. There were more dynamic recrystallization (DRX) structures, resulting in fine and ordered martensite blocks. Under the deformation conditions of 0.1~10s-1/1000°C, the proportion of high-angle grain boundaries (HAGBs) decreased from 53.5% to 40.7% as the strain rate increased. Meanwhile, the hot deformation mechanism shifted from discontinuous dynamic recrystallization (DDRX) to the combined effect of DDRX and dynamic recovery (DRV) and finally transformed into DRV. The flow stress derived from the constitutive model was consistent with the experimental results. The activation energy of EH420 marine steel was 3.16×105J/mol. The optimal hot processing parameters were 950~1050°C and 0.01~0.1s-1.

Determination and verification of parameters in the dynamic constitutive for Inconel 718 superalloy

Abstract Inconel 718, which is a nickel-based superalloy material used in aero engines, may be subjected to intense dynamic loading in an accidental engine failure. However, the material models for Inconel 718 employed in existing studies can not describe the mechanical behaviors under complex stress states, high strain rates and elevated temperatures satisfactorily. In this paper, various parameters of a previously proposed dynamic constitutive model for Inconel 718 are determined and verified. First, the parameters of strength, strain rate effect, temperature effect and failure for precipitation hardened Inconel 718 are calibrated against various material tests. Then, the parameters are verified by comparing the numerical results obtained from the dynamic constitutive model with the corresponding ballistic test data. It transpires that the numerical results agree well with the test data, which demonstrates the accuracy and effectiveness of the dynamic constitutive model for Inconel 718. It can also be concluded that the consideration of Lode angle effect and precise descriptions of strain rate and temperature effects are significant for the reproduction of mechanical responses of Inconel 718 plates under intense dynamic loadings in numerical simulations.

New constitutive model and hot processing map for A100 steel based on high-temperature flow behavior

To predict the flow behavior and identify the optimal hot processing window for A100 steel, a constitutive model and a hot processing map were established using true stress-strain data extracted from isothermal compression tests performed at temperatures ranging from 1073 to 1353 K and strain rates varying between 0.01 and 10 s−1. The results indicate a strong linear trend between the logarithmic stress and the reciprocal of temperature, along with a significant quadratic relationship between the logarithmic stress and logarithmic strain rate. With a correlation coefficient of 0.9913, the new constitutive model demonstrates an excellent predictive capability for the flow behavior of A100 steel. A significant dynamic recrystallization occurs when the energy dissipation rate exceeds 25 %, resulting in a uniform equiaxed grain structure after deformation. The unstable regions primarily occur in high strain rate and low-temperature zones, where the microstructures are typically coarse and elongated. This structural characteristic adversely affects the mechanical properties. Avoiding these conditions during hot forming of A100 steel is crucial. The optimal hot forming windows for A100 steel are achieved within a temperature range of 1153–1353K and a strain rate range of 0.01–10 s−1, where complete dynamic recrystallization occurs.