Combined Effects Of Strain Rate Research Articles

Hot deformation behavior and microstructure evolution model of 7055 aluminum alloy

Hot compression tests were conducted on 7055 aluminum alloy under different strain rates, temperatures, and reduction ratios. The influence of deformation parameters on microstructure evolution and hot deformation behavior was studied through EBSD and TEM characterization. An Arrhenius constitutive model was established and the recovery and recrystallization characteristics of the alloy under different conditions were analyzed. Results showed that the softening mechanism during the hot compression process of 7055 aluminum alloy was mainly attributed to recovery and partial recrystallization. The Zener-Holloman (Z) parameter was utilized to reveal the combined effects of strain rate and temperature on recrystallization behavior. Under conditions of high LnZ values (20 < LnZ), the alloy exhibited predominantly discontinuous dynamic recrystallization (DDRX) characteristics, while at low LnZ values (14 < LnZ <17), it displayed significant continuous dynamic recrystallization (CDRX) characteristics. The alloy showed a coexistence of CDRX and DDRX phenomena under conditions of moderate LnZ values (17<LnZ <20). In addition, based on the characterization, statistical analysis, and examination of the hot-compressed microstructure of the 7055 aluminum alloy, models for recrystallization fraction, grain size evolution, and deformed grain size were established, and an average grain size model was further developed. Comparison between the finite element simulation results based on the models and experimental results demonstrated good agreement in predicting the average grain size.

Experiment and meso-scale modelling on combined effects of strain rate and specimen size on uniaxial-compressive failures of concrete

This paper presents experimental and meso-scale modelling studies on the combined effects of strain-rate and specimen size on uniaxial compressive failure behaviour of concrete. A series of uniaxial compressive tests and meso-scale simulations were conducted on concrete with various specimen sizes under different strain-rates covering the strain-rate range of seismic load, with special focus on the quantitative contribution of end-friction to compressive strength and its corresponding strain-rate effect as well as size effect. Results indicate that the uniaxial compressive failure with end-friction follows an hourglass failure pattern while that without end-friction exhibits a columnar failure pattern. The end-friction effect can form different confined zone distributions for various sized specimens, which can cause the contribution of end-friction to compressive strength is size dependent as well as enhance the influence of specimen size on static and dynamic strength. The contribution proportion of end-friction to compressive strength is around 20∼25%. Moreover, larger-sized specimen performs a stronger strain-rate effect and the increasing strain-rate can weaken the influence of specimen size on the real compressive strength. The proposed real DIF empirical formula considering the size-dependency (covering the low strain-rate range) can well estimate the strain-rate effect for concrete with different sizes, which can provide a valuable reference for the numerical calculation of dynamic mechanical response and the safety design of concrete structures.

Experimental study on the competing effects of strain rate and water weakening on compressive strength of saturated rocks

Measuring the rock compressive strength under combined effects of strain rate and water weakening is of great importance and at the same time a major issue for engineers. In this study, we explore the ability to detangle the contributions of strain rate and water-weakening effects on rock compressive strength within a wide static and dynamic strain rate range. To this end, we conduct a series of compression tests and acoustic emission (AE) tests on two types of rock with specific mineral compositions (i.e., limestone and granite). The correlations between rock compressive strength, including static compressive strength σcs and dynamic compressive strength σcd, and water-weakening factors fw with strain rate are derived. The experimental AE waveform data is analyzed using a new methodology named statistical analysis of dominant frequency, from which we infer the intrinsic rock progressive failure and evaluate the competing effects of water weakening and strain rate. Our results show that water saturation causes a drastic loss in the compressive strength of limestone and a small reduction in the compressive strength of granite. The strain rate effect governs the changes in the compressive strength of dry rocks, characterizing a reduction in low dominant frequencies of AE waveforms with increasing strain rates. Whether the strain rate effect or water-weakening effect plays a dominant role depends largely on the rock types and loading regimes. We proposed that the primary effects on σcs of saturated limestone are strain rate under relatively low static strain rate (lower than 8.33 × 10−5 s−1) and pore water pressure under relatively high static strain rate (beyond 8.33 × 10−5 s−1), respectively, and that on σcd of saturated limestone is strain rate. The variations of σcs and σcd of saturated granite are both determined by the strain rate effect within the strain rate range investigated. Additionally, the exertions of various water-weakening effects of limestone and granite at different strain rates, which are responsible for their fw variations, are evaluated in detail.

On strain rate and temperature dependent mechanical properties and constitutive models for additively manufactured polylactic acid (PLA) materials

Fused deposition modeling (FDM) has demonstrated its effectiveness in the additive manufacturing (AM) field thanks to its numerous merits, such as low cost and ease of implementation. Polymeric polylactic acid (PLA) has been widely used in FDM attributed to its recyclable, renewable, degradable and biocompatible characteristics. However, the material properties of polymeric materials can be largely affected by temperature and strain rate; and the mechanical behavior of polymer printed by FDM are fairly different from those manufactured by traditional technology. In this study, uniaxial tensile tests of the PLA specimens printed by FDM are performed under different strain rates and temperatures. For the first time, the digital image correlation (DIC) technique is employed to capture the surface strain of the AM specimens under loading, allowing us to quantify thermal stress concentration in the FDM printed polymer. Significant strain localization induced by the embrittlement of PLA is identified by the DIC system. The scanning electron microscope (SEM) technique is used to characterize the failure modes and failure mechanisms of the printed PLA samples. With increasing strain rate or decreasing temperature, the ductile to brittle failure modes can be observed by SEM. The modified Zener model is developed here to predict the stress–strain responses accounting for the combined effects of strain rate and temperature with proper modeling accuracy. The Cowper–Symonds material model is also employed to describe the effect of the strain rate on yield strength with a maximum 3.2% relative error between the experimental results and the theoretical model. Further, the yield strength, failure strain and Young’s modulus show a strong linear correlation with temperature. This study is anticipated to provide an effective and precise material model for the mechanical analysis of composite structural components made by the additive manufacturing process.

The role of strain rate and texture in the deformation of commercially pure titanium at cryogenic temperature

In this work, we explore the effect of strain rate and crystallographic texture on the hardening behaviour and ductility of grade 2 commercially pure titanium (CP–Ti) plate at both room (298 K) and cryogenic temperature (123 K). EBSD technique was used to characterise the microstructural features and analyse the deformation twins and active slip systems in α-Ti. Using the SEM fractography, the necking resistance was estimated by measuring the reduction of cross-sectional area. As the strain rate decreases, the elongation was improved with the enhancement of strain-hardening and necking resistance, whereas this behaviour was relatively strain rate insensitive at 298 K. Consequently, the total elongations were increased from 38% (298 K) to 65% (123 K), and from 28% (298 K) to 35% (123 K) in tension parallel and transverse to the rolling direction of the plate, respectively. The combined effect of strain rate and (cryogenic) temperature affected the transition of deformation mechanisms involved in the twinning and dislocation slip, thereby leading to the three or four multi-stage strain-hardening behaviour. The results reveal that in addition to the dislocation slip, the deformation twinning contributed to the strain-hardening, and improvement of total elongation of α-titanium at cryogenic temperature.

Comparative Study of the Dynamic Deformation of Pure Molybdenum at High Strain Rates and High Temperatures.

To study the dynamic plastic properties of high-purity molybdenum materials at high temperature and high strain rate, we designed tests to compare the mechanical behaviour of two high-purity molybdenum materials with different purities and two with different processing deformation conditions under dynamic impact compression in the temperature range of 297–1273 K. We analysed the molybdenum materials’ sensitivities to the strain-hardening effect, strain rate-strengthening effect, and temperature-softening effect as well as the comprehensive response to the combined effect of the strain rate and temperature, the adiabatic impact process, and the microstructure at high temperature and high strain rate. Furthermore, based on a modified Johnson–Cook constitutive model, we quantitatively analysed the flow stresses in these materials. The calculation results strongly agree with the test results. Our findings indicate that the high-purity molybdenum materials show consistent sensitivity to the combined effect of strain rate and temperature regarding the dynamic plastic properties. The materials with higher purity are less sensitive to the combined effect of the strain rate and temperature, and those with less processing deformation experience more pronounced strain-hardening effects. Under high strain rate at room temperature, these materials are highly susceptible to impact embrittlement and decreases in dynamic plastic properties due to intergranular fracture in the internal microstructure. However, increasing the impact environment temperature can significantly improve their plastic properties. The higher the temperature, the better the plastic properties and the higher the impact toughness.

Modelling the influence of strain and strain rate on the thermal softening during dynamic loading of ductile metals

Although the combined effect of strain rate and temperature on the behaviour of metals is widely recognized, no universally accepted viewpoints are available about the physical phenomena. Experiments on a highly ductile A2-70 steel, performed at moderate dynamic rates (10 s-1) and different initial temperatures (20 to 150 °C), are firstly aimed here at assessing whether the thermal softening previously verified at static rates on the same steel is also suitable for describing now the mixed effect of dynamic rates and consequent variable temperatures, or further contributions to the thermal softening are necessary for describing such mixed effects. A general multiplicative model of the dynamic hardening is proposed, based on a static flow curve at room temperature to be increased by the dynamic amplification and to be decreased by the thermal softening, the latter incorporating the known “static component” depending on both strain and constant temperatures, together with a new “dynamic component” incorporating the dependence on the temperature variation and promoted by fast straining. The dynamic amplification of the stress is then obtained from another series of dynamic tests ran at initial room temperature and four nominal strain rates between 1 and 1800 s-1. The trend obtained is compatible with the seizing of the strain rate effect beyond necking onset, already found for other metals in previous works. All the experiments are based on the acquisition of the current load (by load cells for the testing machine and by strain gauges for the Hopkinson bar) and of the current cross section through optical diameter measurements by a fast camera; then, the effective current values of true stress-true strain-true strain rate are measured on a semi-local basis over the neck section at different instants during the test.

Dynamic compressive properties of dry and saturated coral rocks at high strain rates

Coral rock is characterized by a high porosity of 48.51 ± 5.43% and a low compressive strength of 9.91 MPa due to its biological origin. To experimentally investigate the uniaxial compressive behaviors of both air-dried and fully saturated coral rocks, the quasi-static and dynamic compression tests were performed employing an electro-hydraulic servo-controlled device and a split Hopkinson pressure bar (SHPB) apparatus. The combined effects of strain rate and water saturation on the mechanical properties of coral rock were assessed in terms of the uniaxial compressive strength, Young's modulus, brittleness, energy dissipation as well as the failure pattern. The dynamic uniaxial compressive strength and Young's modulus of saturated coral rocks is consistently lower than those under dry condition, while the losses in them reduces with an increase in stain rate. The coral rock behaves in a more brittle manner in dry state than in saturated state, which is validated by the digital image correlation (DIC) in conjunction with high-speed camera images. Likewise, the change in brittleness or specific energy absorption (SEA) with strain rate under dry and saturated conditions exhibits a similar trend to the dynamic compressive strength. Furthermore, the dynamic failure of dry coral rock appears to be more dependent on the inherent flaws and defects than the saturated one, as the failure pattern doesn't follow a fixed shearing or splitting fracture mode. Overall, the difference of dynamic behaviors between dry and saturated coral rocks are mainly controlled by the coupling weakening and strengthening effects induced by free water. The strengthening effect of water saturation is manifested by making the strength and deformability of coral rock more sensitive to the loading strain rate.

Deformation mechanism and force modelling of the grinding of YAG single crystals

YAG single crystals are the primary host materials for solid-state lasers at multi-kW scale and must be processed using ultra-precision grinding to achieve a satisfactory dimensional precision and surface integrity. However, the deformation mechanism of YAG crystals is not well understood, which has thus hindered the development of high efficiency grinding technology for the crystals. In this work, precision grinding of YAG single crystals was investigated. Ductile-like surfaces that are free of cracks and brittle-ductile surfaces that consist of fractured spots and ductile striations were found after grinding. The deformation mechanisms associated with the two types of surfaces were explored with the aid of transmission electron microscopy (TEM). The results indicated that the deformation involved in the formation of the ductile-like surface was mainly caused by the slippage of (0 0 1) crystal planes, along with the formation of dislocations and stacking faults and the distortion of atomic planes. The brittle-ductile surfaces were generated by the plastic deformation due to the formation of nanocrystals and nanovoids, combined with brittle fracture caused by the crack propagation initiated at intersections of slip lines. A theoretical model was developed to predict the grinding force in the ductile-like grinding process, which has taken the combined effect of strain rate, random distribution of abrasive radii and elastic-to-plastic transition depth into account for the first time. The key model parameters were obtained using a genetic algorithm trained using the experimental force data. The modelled force agrees well with the measured. This model enabled an in-depth understanding of the deformation mechanism of a crystal solid involved in ultraprecision grinding and the effect of strain rate on its material removal.

Numerical modelling of a steel catenary riser section in the touchdown zone under cyclic loading

The fatigue life of steel catenary risers is significantly influenced by cyclic riser–seabed–water interaction in the touchdown zone. In this study, the penetration and extraction of a shallow embedded riser section, subjected to cyclic vertical loading, are simulated using a computational fluid dynamics approach with ANSYS CFX. An empirical strength degradation model is proposed for soil softening due to undrained remoulding and clay–water interaction in the highly sheared interface, termed ‘shear wetting.’ The combined effects of strain rate and softening on the mobilized shear strength of deepwater offshore clay are implemented in CFX. A sufficiently large number of loading cycles is simulated using this computationally efficient numerical technique to achieve a stable response. A significantly large reduction of vertical resistance of a shallowly embedded riser section due to cyclic loading, as observed in physical model tests, is obtained using the proposed strength degradation model with shear wetting, which cannot be explained simply by undrained remoulding.

On the microstructure evolution in friction stir processed 2507 super duplex stainless steel and its effect on tensile behaviour at ambient and elevated temperatures

The microstructures and mechanical properties of friction stir processed 2507 super duplex stainless steel were examined. Experimental results revealed that there is an optimum traverse speed for a given rotational speed that gives minimum grain size. The individual and synergistic effects of FSP parameters such as heat input, strain rate and strain on the grain size of the material were evaluated. The results indicate that counteracting effect of heat input and the combined effect of strain rate and strain results in achieving minimum grain size at an intermediate traverse to rotation speed ratio. The twin boundaries (particularly Σ3 CSL boundaries) in the stir zone of friction stir processed material reduced considerably compared to that in the base material. Both the base material and the friction stir processed material with the smallest grain size achieved were subjected to tensile testing at ambient and elevated temperatures under different strain rates. The results obtained are presented and discussed here.

Effect of the strain rate on the intermediate temperature brittleness in Zr-based bulk metallic glasses

In this work, the effect of strain rate on the ductility, intermediate temperature brittleness and fracture surface of Zr-based BMG over a wide range of temperatures from 0.1 Tg to near Tg, has been systematically investigated. The results showed two remarkable ductile to brittle transition at low cryogenic and intermediate temperatures. At low temperatures, below 0.4 Tg, the activation of diffusion mediated phenomena is negligible and the combined effects of strain rate and temperature contribute to the plasticity of material by changing the STZ volume, hence the possibility of forming multiple shear bands. At the temperature range from 0.4 Tg to the temperature at which the intermediate brittleness happens, the activation of fewer STZs takes place during inelastic shuffling of caged atoms by nearly constant loss (NCL). At higher temperatures, with the onset of Johari-Goldstein β-relaxation, which is accompanied by the NCL caged dynamics termination, more atoms can leave the cages and cooperate together, thus facilitate the activation of STZs. Furthermore, increase of strain rate shifts the intermediate temperatures brittleness to higher temperatures. Moreover, an intriguing correlation between the shear offset and the width of stable crack region with ductility is reported by studying the fracture surface topography.

Numerical simulation of strain rate effect on the inelastic behavior of metal matrix composites

AbstractThe primary goal of this paper is to investigate the combined effects of strain rate and microscopic parameters (fiber off-axis orientation, array pattern and cross-sectional shape) on the mechanical behavior of metal matrix composites (MMCs). To this end, a rate-dependent micromechanical model by the combination of finite-volume theory and Bodner-Partom viscoplastic model is developed to analyze the inelastic response of MMCs. In the simulations, the fibers are modeled as linearly elastic while the metal matrix exhibits viscoplasticity. The macroscopic stress-strain response, local stress and strain fields are obtained simultaneously. An acceptable agreement has been found between the model’s prediction and finite-element results, which demonstrates the good predictive capabilities of the proposed method. It is concluded that the composite response is strongly affected by strain rate, fiber array pattern and cross-sectional shape in the elastic-plastic region but to a lesser extent in the elastic region. Furthermore, the clustering array provides stiffer response than random and square ones; the square fiber predicts stiffer response than circular and elliptical ones. However, increasing the strain rate will weaken the influence of clustering array and square fibers.

Comparison between dynamic mechanical properties of dam and sieved concrete under biaxial tension-compression

A comparative study on the dynamic properties of dam and sieved concrete was conducted based on dynamic biaxial tensile-compressive tests. Specimens were designed to be prismatic shape with a size of 250×250×400mm for dam concrete and 150×150×300mm for sieved concrete, respectively. Each specimen was biaxially loaded by constant tensile-compressive (T-C) stress ratios (0:−1, 0.05:−1, 0.1:−1, 0.25:−1, 0.5:−1, and ∞) at the strain rate of 10−5s−1, 10−4s−1, 10−3s−1, and 10−2s−1 by a servo-hydraulic multi-axial testing machine. The failure modes of specimens have been compared under various biaxial T-C loading conditions at each strain rate, thus the fracture surface of sieved concrete specimen is smoother than dam concrete. The dynamic strength of dam concrete is lower than sieved concrete under the same loading condition, and the ratio of them is insensitive to strain rate. The growth rates of dynamic strength for dam concrete is consistent with sieved concrete, whereas much larger than ordinary concrete. By regression of the test results, the dynamic T-C failure criterions for dam and sieved concrete were proposed after considering the combined effects of strain rate and stress ratio.

Numerical investigation on the penetration of gravity installed anchors by a coupled Eulerian–Lagrangian approach

Gravity installed anchors (GIAs) are released from a height of 30–150m above the seabed, achieving velocities up to 19–35m/s at the seabed, and embed to depths of 1.0–2.4 times the anchor length. Challenges associated with GIAs include the prediction of anchor initial embedment depth, which determines the holding capacity of the anchor. Based on the coupled Eulerian–Lagrangian approach, a numerical framework is proposed in this paper to predict the embedment depth of GIAs, considering the effects of soil strain rate, soil strain-softening and hydrodynamic drag (modeled using a concentrated force), with the anchor-soil friction described appropriately. GIAs are influenced by the hydrodynamic drag before penetrating into the soil completely, hence the anchor accelerates less than the previous investigations in shallow penetration, even decelerates directly at the terminal impact velocity. The hydrodynamic drag has more influence on OMNI-Max anchors (with an error of ∼4.5%) than torpedo anchors, and the effect becomes more significant with increasing impact velocity. An extensive parametric study is carried out by varying the impact velocity, strain rate and strain-softening parameters, frictional coefficient, and soil undrained shear strength. It is concluded that the dominant factor affecting the penetration is the soil undrained shear strength, then are the impact velocity, strain rate dependency and frictional coefficient, and the minimal is the strain-softening of soil. In addition, although the strain rate dependency is partly compensated by the softening, the anchor embedment depth accounting for the effects of strain rate and strain-softening is lower than that for ideal Tresca soil. Strain rate dependency dominates the combined effects of strain rate and strain-softening in the dynamic installation of GIAs, on which should pay more attention, especially for the calibration of the related parameters and the measured solutions. In the end, the theoretical model based on the bearing resistance method is extended by accounting for the hydrodynamic drag effect.

Hot deformation behaviour and microstructural evolution of biomedical Ti-13Nb-13Zr alloy in high strain rate range

The deformation behaviour and microstructural evolution of biomedical Ti-13Nb-13Zr alloy are investigated at strain rates of 1×103s−1, 2×103s−1 and 3×103s−1 and temperatures of 25°C, 650°C and 800°C using a compressive split-Hopkinson pressure bar (SHPB) system. The results show that the flow stress, strain rate sensitivity and temperature sensitivity increase with increasing strain rate or decreasing temperature. In addition, adiabatic shearing occurs in the specimens deformed at 25°C and 650°C under the maximum strain rate of 3×103s−1. For the specimen deformed at 25°C, the adiabatic shear band results in catastrophic failure. The microstructural observations reveal that single β phase is formed under the highest temperature of 800°C. The volume fraction of α' martensite and the dislocation density increase, but the grain size decreases, as the temperature is reduced or the strain rate increased. The average thickness of the α' laths reduces as the strain rate and temperature increase. The interaction between the grain size, dislocation density and α'martensite volume fraction leads to a significant strengthening effect. The higher flow stress caused by this strengthening effect can be estimated using an empirical model of the form σ=σo+KD−1/2+K'ρ1/2+Ωξ, where K, K'and Ω are equal to 69.82MPaμm1/2, 6.62 MPaμm and 105.4MPa, respectively. The average error in the flow stress estimates is found to be just 2.04% for the temperature and strain rate conditions considered in the present study. Overall, the results presented in this study provide a useful insight into the combined effects of strain rate and temperature on the hot working behaviour and deformability of Ti-13Nb-13Zr alloy. In general, the results confirm that Ti-13Nb-13Zr alloy is well suited to the fabrication of orthopaedic implant devices and structural components in the biomedical and engineering fields, respectively.

ACMEG-TVP: A thermoviscoplastic constitutive model for geomaterials

In this paper, a thermoviscoplastic constitutive model for geomaterials is presented. The model is formulated based on two aspects: (i) the nonstationary flow surface theory, which is used to describe the viscous behaviour of geomaterials, and (ii) the thermoplasticity concept, which is adopted to introduce the effect of temperature on geomaterials. In the model, the yield surface evolves with the viscoplastic strain, viscoplastic strain rate and temperature. Thus, it allows the description of combined effects of strain rate and temperature on the mechanical behaviour of geomaterials. The model has been used to simulate various tests involving different thermomechanical loading paths, including non-isothermal constant rate of strain tests, cyclic heating and cooling tests, creep tests with temperature changes and stress relaxation tests. The simulation results agree well with measurements, demonstrating the capacity of the proposed model to reproduce the various thermoviscoplastic behaviour of geomaterials.

Deformation behavior and microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures

The impact deformation behavior and associated microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures are investigated using a compressive split-Hopkinson pressure bar (SHPB) system. Cylindrical specimens are deformed at strain rates of 1×103s−1, 2×103s−1, 3×103s−1 and 5×103s−1 and temperatures of 0°C, −100°C and −196°C. It is shown that the flow stress is strongly dependent on the strain rate and temperature. For a given temperature, the flow stress varies with the strain rate in accordance with a power law relation with an average exponent of 0.157 and an activation energy of 0.7kJ/mol. Moreover, the coupled effects of the strain rate and temperature on the flow stress are adequately described by the Zener-Hollomon parameter (Z). For all test temperatures, catastrophic failure occurs only under the highest strain rate of 5×103s−1, and is the result of adiabatic shear. An increasing strain rate or reducing temperature leads to a greater dislocation density and a smaller grain size. Finally, the dependence of the flow stress on the microstructural properties of the impacted 7075-T6 specimens is well described by a specific Hall-Petch constitutive model with constants of K= 108.3MPaμm1/2 and K′=16.1MPaμm, respectively. Overall, the results presented in this study provide a useful insight into the combined effects of strain rate and temperature on the flow resistance and deformability of 7075-T6 alloy and confirm that 7075-T6 is well suited to the fabrication of fuel tanks and related structural components in the aerospace field.

Effect of strain rate on pore pressure evolution and effective stress path of soft soil under different stress history conditions

Soft marine soils are highly plastic fine-grained soils and known for their high compressibility, large water content and low shear strength behaviour. The previous research on soft soils is restricted to stress–strain response under conventional loading conditions with and without its treatment. The effect of strain rate on pore pressure evolution and effective stress path of soft soil under different stress history conditions has not been explored. In the current research, an extensive experimental research has been performed on Kanjurmarg soft marine soil to evaluate its pore pressure evolution, effective stress path, obliquity and effective stress ratio at different strain rates and varying stress history conditions. A wide range of strain rate, 0.005% per min to 5% per min, was used to perform the CU triaxial tests on soft soil. Such large strain rates are used to analyse the behaviour of soil under various field conditions such as rapid excavation, rapid application of surcharge, aircraft wheel loading on runways, fast installation process of pile and projectile penetration. The effect of stress history on soft soil was also explored for OCR values of 1, 2, 5, 10 at different strain rates. The soil was also tested at different confining pressures at varying strain rates to evaluate the combined effect of strain rate and confining pressure.

Flow and fracture characteristics of near alpha titanium alloy

To understand the flow and fracture behavior of near-α titanium alloy, the influence of stress triaxiality and strain rate on the failure behavior of this alloy was considered. The combined effect of strain rate, temperature and stress triaxiality on the behavior was studied by testing both smooth and notched specimens. Johnson-Cook (J-C) constitutive and fracture models were established based on high strain rate tensile data obtained from Split hopkinson tension bar (SHTB) and quasi-static tests. The Johnson Cook constitutive and fracture models have been calibrated. A modified Johnson–Cook model was established and proved to have high accuracy. The calibrated model has been validated by simulating the tension tests at various triaxialities using ANSYS autodyn software. Finite element simulations were used to predict the effective plastic strain versus triaxiality history within the deforming specimens. The fracture surfaces of specimens tested under various strain rates and temperatures were studied under scanning electron microscopy (SEM).