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A practical inverse method based on the hybrid experiment-finite element (FE) simulation is proposed for identifying strain rate sensitivity of a metal covering intermediate to dynamic loading conditions. The methodology uses the dynamic split Hopkinson pressure bar (SHPB) test for measuring mechanical responses at medium strain rates by optimizing temperature increase, non-uniform strain rate distributed in the non-standard notched SHPB specimens. From the standard dynamic SHPB test, the thermal softening index of the Johnson–Cook (JC) model is first determined by fitting the FE simulation to temperature changes in the specimen. The discrepancy between the measured and predicted flow stresses with the conventional JC model can be attributed to the assumption of constant strain rate sensitivity. Therefore, the new approach using the notched SHPB specimens under dynamic loadings is introduced to identify mechanical responses covering a broader range of strain rate. Finally, the strain rate sensitivity parameter in the JC model as a function of strain rate is evaluated through the inverse FE scheme, in which the sigmoidal function is determined to be optimum by predicting the flow stresses under wider range of strain rate, especially in the intermediate range of strain rate. The present study provides a new methodology based on hybrid experiment and numerical simulation to fill the gap in predicting mechanical responses between quasi-static and dynamic tests using commonly available tensile test and SHPB test. [ABSTRACT FROM AUTHOR]

Based on the true stress–strain data obtained from dynamic compression experiments using split Hopkinson pressure bar, constitutive models including the Johnson–Cook model, modified Johnson–Cook model, Mechanical Threshold Stress model, and modified Arrhenius-type constitutive model are developed to describe the plastic flow behavior of GCr15 steel over a temperature range of 298 to 873 K and strain rates from 460 to 3940 s−1. The material parameters for the models are optimized using the Grey Wolf Optimizer, and the predictive performance is evaluated based on the correlation coefficient and average absolute relative error. Furthermore, the micromorphology of the specimen after impact is observed using a scanning electron microscope. The results indicate that all four constitutive models effectively reflect the plastic flow behavior of GCr15 steel. The modified Johnson–Cook model is more effective and accurate than the Johnson–Cook model, Mechanical Threshold Stress model, and modified Arrhenius-type constitutive model for predicting the dynamic compression behavior of GCr15 steel, with a correlation coefficient of 0.9711, an average absolute relative error of 2.6501% and a mean relative error of −0.2899%. [ABSTRACT FROM AUTHOR]

The modified Johnson–Cook (MJC) material model is widely used in simulation under high-velocity impact. There was a need to estimate a strain rate parameter for the application to the impact analysis, where the method typically used is the Split Hopkinson bar. However, this method had a limit to the experiment of strain rate. This study proposed to estimate the strain rate parameter of the MJC model based on the impact energy and obtained a parameter. The proposed method of strain rate parameter calculation uses strain parameters to estimate from the drop weight impact and high-velocity impact experiments. Then, the ballistic experiment and analysis were carried out with the target of the plate and cylindrical shape. These analysis results were then compared with those obtained from the experiment. The penetration velocities of plates could be predicted with an error of a maximum of approximately 3.7%. The penetration shape of the cylindrical target has a similar result shape according to impact velocity and had an error of approximately 6%. [ABSTRACT FROM AUTHOR]

Isothermal compression behaviors of 5CrNiMoV steel were studied at temperatures of 870, 800, 750, and 700 °C, with strain rates of 0.001, 0.005, 0.01, 0.05, and 0.1 s−1, the compression temperatures 870 and 800 °C are above Ac3, as well as 750 and 700 °C below Ac3 temperature. The Modified Johnson–Cook (MJC) model and the Strain–Compensated Arrhenius (SCA) model were employed to demonstrate the relationship between the flow stress and the compression parameters. The correlation coefficient (R) and average absolute relative error (AARE) between the calculational and experimental flow stress were used to evaluate the accuracy of the two models. The results show that the effect of dynamic softening on flow stress is much more significant at higher temperatures and lower strain rates, while this effect is not obvious when the strain rate exceeds 0.005 s−1 with the temperature below Ac3. The MJC model has a good accuracy close to the reference conditions (0.001 s−1 and 700 °C), and it is suitable to predict the plastic behavior when the flow stress is lower than 200 Mpa. The unbiased AARE values were 6.82 and 5.71 for MJC model and SCA model, respectively, which implied the SCA model has a higher accuracy than the MJC model. The SCA model was believed to be capable of being used to illustrate the thermomechanical behavior of 5CrNiMoV tool steel in a wide range of plastic deformation conditions. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration (UV) assisted plastic forming technology is an ideal way to improve the formability of titanium and its alloys at room temperature, due to the softening effect which is more effective than thermal input. Thus, UV assisted compression test of commercially pure titanium is carried out and the deformation behavior is focused in this study. For an accurate prediction of the flow behavior and further application in UV forming process, the original Johnson–Cook (JC) model and its modified formulae have been adopted to construct the constitutive relation of pure titanium deformed with high-frequency oscillation. The yield stress reduction is related to both the amplitude and its square. The other material constants in JC model are established as the function of the amplitude. The comparative analysis of the predicted stress through the built JC model with the measured one is performed, showing the improved JC model can precisely describe the stress-strain relation in a large deformation range at different vibration amplitudes and strain rates.

Constitutive models can be used as a powerful tool to predict the complex behavior of materials under different deformation conditions. These equations can model and control the flow behavior of materials with appropriate accuracy by considering the parameters affecting the behavior of the material. In this study, a modified Johnson- Cook model has been developed to predict the hot working behavior of L80 micro alloy steel at various deformation parameters such as temperature, strain rate, and strain. In order to develop this model, experimental data related to hot compression tests at a temperature range of 1173-1373 K and strain rates of 0.001-1 s-1 have been used. The results of the microstructure correctly describe the flow behavior of the material. The results show that the developed model, taking into account the softening effects of temperature as well as strain and strain rate hardening, provides a good prediction of the hot working behavior of micro-alloy steel and this developed model can be used to simulate the production processes of this steel at high temperatures. [ABSTRACT FROM AUTHOR]

In this paper, specimens were first pre-stretched to different pre-strain coefficients (0, 0.4 and 0.8) under quasi-static tensile for AA6061-O aluminum alloy. Then, the specimens with different pre-strain coefficients were stretched by a high-speed tensile machine (HTM) at different strain rates (200 s− 1, 400 s− 1 and 600 s− 1). Digital image correlation (DIC) technique was employed to measure the strains. The results showed that the yield ratio increased significantly with the pre-strain increased. As the pre-strain coefficient increased, high-speed tensile strain limitation decreased and the total tensile strain limitation increased. A modified Johnson-Cook (JC) model considering pre-strain coefficient was proposed. Numerical simulations were performed using LS-DYNA with the modified JC model. The strain field of the specimen taken by the camera agreed well with the simulated strain field. [ABSTRACT FROM AUTHOR]

Isothermal compression behaviors of 5CrNiMoV steel were studied at temperatures of 870, 800, 750, and 700 °C, with strain rates of 0.001, 0.005, 0.01, 0.05, and 0.1 s−1, the compression temperatures 870 and 800 °C are above Ac3, as well as 750 and 700 °C below Ac3 temperature. The Modified Johnson–Cook (MJC) model and the Strain–Compensated Arrhenius (SCA) model were employed to demonstrate the relationship between the flow stress and the compression parameters. The correlation coefficient (R) and average absolute relative error (AARE) between the calculational and experimental flow stress were used to evaluate the accuracy of the two models. The results show that the effect of dynamic softening on flow stress is much more significant at higher temperatures and lower strain rates, while this effect is not obvious when the strain rate exceeds 0.005 s−1 with the temperature below Ac3. The MJC model has a good accuracy close to the reference conditions (0.001 s−1 and 700 °C), and it is suitable to predict the plastic behavior when the flow stress is lower than 200 Mpa. The unbiased AARE values were 6.82 and 5.71 for MJC model and SCA model, respectively, which implied the SCA model has a higher accuracy than the MJC model. The SCA model was believed to be capable of being used to illustrate the thermomechanical behavior of 5CrNiMoV tool steel in a wide range of plastic deformation conditions.

Hot compression tests for 2219/TiB2 Al-matrix composite were conducted on a Gleeble-3500 isothermal simulator in the temperature range of 300~500°C and strain rates of 0.01, 0.1, 1, 10s-1 to obtain true stress strain curves. The original Johnson-Cook model was calculated and used to describe the constitutive relationship of hot deformation behavior of this composite. After precision evaluation and analysis, a new modified Johnson-Cook model was proposed. Comparing with the original model, the new model has a lower absolute average relative error (AARE) of 6.4415% and a higher relative error (R) of 0.9852, which indicates better prediction precision. Meanwhile, to understand the intrinsic workability of this composite, processing map based on dynamic materials model was constructed. Two stable regions locating at 300~400°C&0.01~0.1s-1 and 420~500°C &0.01~1s-1 were identified by the processing map and the instable microstructure in the instability region validated the reliability of the processing map. Furthermore, the microstructure evolution was analyzed and the results revealed that the θ-phase reduced with the increasing temperature.

The mechanical behavior of AZ31B magnesium alloy was studied through uniaxial tensile tests at strain rates of 0.001, 1, 100, and 1000/s. The results show that an increase in the strain rate results in a gradual increase in the flow stress. Considering that the original Johnson–Cook (J–C) model cannot adequately describe the flow stress of AZ31 magnesium alloy at different strain rates, a rate-dependent modified Johnson–Cook (M-J–C) model was proposed, and the coefficients were calibrated according to the experimental results. The calibration and validation show that the M-J–C model has a high accuracy in characterizing the flow stress of AZ31B magnesium alloy and can well predict the hardening curve of ZK60 and AM60 magnesium alloys at different strain rates in the literature. In addition, the variation in the fracture strain with different strain rates was characterized. The fractography was studied to reveal the mechanism of underlying fracture. The proposed M-J–C constitutive model combined with a failure criterion was developed and coded into LS-DYNA through the user subroutine UMAT. The comparison between the simulation and the experiment shows that the developed subroutine is accurate enough to simulate the plastic and fracture behaviors of AZ31B magnesium alloy at different strain rates. [ABSTRACT FROM AUTHOR]

The SnSbCu alloy is widely used as the material for the main bearing in low-speed marine engines, and an accurate constitutive model is the foundation for studying the frictional behaviors of bearings. In this work, the compressive flow behaviors of the SnSbCu alloy were considered under the different strain rates (1000-5000 s−1) and temperatures (20-110 °C) by quasi-static and split-Hopkinson pressure bar dynamic compression tests. First, the original Johnson–Cook model was used to describe the constitutive relation of the SnSbCu alloy at high strain rates, and the results predicted by the original model showed relatively large errors compared with the experimental results since the coupled effect of temperature and strain rate was omitted. Then, a modified Johnson–Cook constitutive model was developed to describe the compressive flow behaviors of the SnSbCu alloy, and the results predicted by this modified model agreed well with the experimental data. Moreover, a finite element analysis was also conducted to verify the accuracy of the modified Johnson–Cook model. [ABSTRACT FROM AUTHOR]

The ductile fracture behavior of 17-4PH martensitic stainless steel at high temperature was investigated based on the experimental data of hot uniaxial tensile test. The elongation and reduction of area indicated that the ductility was mainly enhanced during the deformation at the temperature 1150 °C–1200 °C with high strain rate more than 0.1 s ^−1 . The hot flow stress curves were obtained from the tensile experiments, and the true strain of necking initiation was determined by analyzing the contours of fractured specimens. Then, the true stress-true strain data of the deformations before necking were adopted to establish the tensile flow stress model. In order to express the combined influences of the strain, strain rate and temperature on flow stress, a modified Johnson-Cook model was proposed to describe the hot constitutive behavior of the presented steel. It indicates that reasonable agreements between the model-predicted results and the experimental data were achieved.

Turning modeling and simulation of different metallic materials using the commercially available Finite Element (FE) softwares is getting prime importance because of saving of time and money in comparison to the costly experiments. Mostly, the numerical analysis of machining process considers a purely isotropic behavior of metallic materials; however, the literature shows that the elastic crystal anisotropy is present in most of the ‘so-called’ isotropic materials. In the present work, the elastic anisotropy is incorporated in the FE simulations along with the effect of grain size. A modified Johnson-Cook ductile material model based on coupled plasticity and damage evolution has been proposed to model the cutting process. The simulation results were compared with experimental data on the turning process of Aluminum alloy (AA2024). It was found that the elastic anisotropy influences the average cutting force up to 5% as compared to the isotropic models while the effect of grain size was more pronounced up to 20%. [ABSTRACT FROM AUTHOR]

In this study, the flow stress behavior of ferritic-pearlitic steel (C45E steel) is investigated through isothermal compression testing at different strain rates (1 s−1, 5 s−1, and 60 s−1) and temperatures ranging from 200 to 700 °C. The stress-strain curves obtained from experimental testing were post-processed to obtain true stress-true plastic strain curves. To fit the experimental data to well-known material models, Johnson-Cook (J-C) model was investigated and found to have a poor fit. Analysis of the flow stress as a function of temperature and strain rate showed that among other deformation mechanisms dynamic strain aging mechanism was active between the temperature range 200 and 400 °C for varying strain rates and J-C model is unable to capture this phenomenon. This lead to the need to modify the J-C model for the material under investigation. Therefore, the original J-C model parameters A, B and n are modified using the polynomial equation to capture its dependence on temperature and strain rate. The results show the ability of the modified J-C model to describe the flow behavior satisfactorily while dynamic strain aging was operative.

In order to establish the constitutive model to predict deformation behavior during quenching process, uniaxial tension behaviors of an as-quenched AA2219 sheet were investigated over a wide temperature range (298-773K) at different strain rates (0.001-1s -1 ) in quasi-static regime. The experimental results show that the flow stress is closely related to temperature and strain rate. The material exhibits negative strain rate sensitivity (SRS) that the flow stress decreases with increase of strain rate below a critical temperature of T c . A model established by Kabirian et al. (Kabirian, F., Khan, A.S., Pandey, A. Int. J. Plast. 2014, 55) based on the KHL model considering the negative to positive SRS shows successful prediction of the flow stress in a temperature range of 296-473K. However, at higher temperatures (473-773K) the measured SRS deviates from the calculated values of Sigmoidal function given by Kabirianet al. with the increase of temperature. Therefore, in this paper, based on an extended Sigmoidal function and a proposed relation between flow stress and the coupling effects of strain and temperature, a modified Johnson-Cook model is proposed to describe the quasi-static stress-strain responses over a wider temperature range. Correlations using the modified model show good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

An accurate prediction of flow behavior of metals considering the combined effects of strain, strain rate and temperature is essential for understanding flow response of metals, and a key requirement for numerical modeling and simulation of machining. Thus, the effects of high strain rate and elevated temperature on the deformation behaviors of FeCr alloy specimen, obtained by laser additive manufacturing (LAM), were investigated by Split Hopkinson Pressure Bar tests with the strain rates of 1000–8000 s −1 and temperature range of 20–800 °C. Strain rate softening effect was found at high strain rate and discussed. Based on the experimental results, the Johnson-Cook model and modified Johnson-Cook model were established for the LAM FeCr alloy. The predictions of these constitutive models were compared using statistical measures like correlation coefficient and absolute average error. Analysis of statistical measures reveals that J-C model has more deviation from the experimental values. Whereas, the predictions of modified J-C model are very close to the experimental results, which is better model for predicting the dynamic behavior of the LAM FeCr alloy. [ABSTRACT FROM AUTHOR]

Tensile tests at different strain rates (0.0002, 0.002, 0.02, 1000 and 3000 s) were carried out for 7N01 aluminum alloy. Low strain rate experiments (0.0002, 0.002 and 0.02 s) were conducted using an electronic mechanical universal testing machine, while high strain rate experiments (1000, 3000 s) were carried out through a split Hopkinson tensile bar. The experimental results showed that 7N01 aluminum alloy is strain rate sensitive. By introducing a correction scheme of the strain rate hardening coefficient, a modified Johnson-Cook model was proposed to describe the flow behaviors of 7N01 aluminum alloy. The proposed model fitted the experimental data better than the original Johnson-Cook model in plastic flow under dynamic condition. Numerical simulations of the dynamic tensile tests were performed using ABAQUS with the modified Johnson-Cook model. Digital image correlation was used together with high-speed photography to study the mechanical characters of specimen at high strain rate. Good correlations between the experiments results, numerical predictions and DIC results are achieved. High accuracy of the modified Johnson-Cook model was validated. [ABSTRACT FROM AUTHOR]

Structural cables are widely adopted around the world in offshore construction, sports stadia, large scale bridges, Ferris wheels and suspended canopy and fabric structures. However, the robustness of such structures to blast or impact is uncertain with a particular concern related to the loss of a primary structural cable when damaged by high velocity blast fragmentation. This paper presents the first ever numerical and experimental study on commonly used high-strength steel spiral strand cables subjected to high velocity fragment impact. Spiral strand cables were impacted by 20 mm fragment simulating projectiles travelling at velocities between 200 and 1400 m/s. Complex 3D non-linear finite element models were developed and carefully compared with experimental tests. The penetration resistance of the cables and resultant damage were studied with respect to fragment impact velocity. It was found that for all the impact velocities, the fragment penetration depth was less than half of the cable diameter demonstrating a considerable amount of resilience. Considering the damage caused, the residual cable breaking strengths were estimated and found to be still higher than the minimum breaking load of an un-damaged cable. The numerical models were also able to reproduce the main features of the impact tests, including the extent of localised damage area, the fragment penetration depth and mode of individual wire failures, thus demonstrating their potential to be widely used in industry for structural resilience and robustness assessments by structural engineers. [ABSTRACT FROM AUTHOR]

Nickel based alloys are extensively used in the aerospace industry due to the excellent corrosion resistance and high mechanical properties that are maintained up to elevated temperatures (600–800 °C). However, these superalloys are classified as difficult-to-cut and therefore modelling and simulation of the machining processes has become a key in the machinability assessment of nickel based alloys. The reliability of Finite Element Models (FEM) largely depends on the quality of input parameters, one of the most relevant being the constitutive material model representing work material behavior under high strain, strain rate and temperatures. In order to develop a reliable material model, the present work deals with a complete characterization of Inconel 718. Uniaxial compression tests at testing temperatures close to those found in machining (21–1050 °C) and high strain rates (10°−10 2 s −1 ) were performed on the Gleeble 3500 testing machine. Moreover, the microstructural analysis and microhardness measurements of the testing samples were performed, in order to correlate the microstructural state with the mechanical properties of the Inconel 718. Based on this experimental work, a new coupled empirical model is proposed to describe the particular behaviour of nickel based alloys at elevated temperatures and high strain rates. This material behaviour model introduces softening phenomena as well as the coupling between the temperature and the strain rate known to occur experimentally, for machining FEM simulations with Inconel 718 superalloy. [ABSTRACT FROM AUTHOR]

The compression mechanical behaviors of 7050-T7451 alloy over a wide range of strain rates were studied. The quasi-static and dynamic uniaxial compression tests were presented over a wide range of strain rates (0.0001 s −1 , 0.01 s −1 , 2500 s −1 , 4000 s −1 , 7500 s −1 and 10,000 s −1 ) and temperatures (20 °C, 100 °C, 200 °C and 270 °C). The work hardening behavior changes from work hardening to flow softening with the increase of plastic strain at dynamic conditions. In addition, the dynamic recrystallization (DRX), grain refining and phase transition were observed from the microstructures of the cross-section of the compressed specimens. The microstructure evolution at dynamic condition leads to a smaller work hardening rate than that at most of the quasi-static conditions, indicating a coupling effect of the work hardening and strain rate for 7050-T7451 alloy. Besides, the calculated average thermal softening rate decreases with the increase of logarithmic strain rate, which indicates a coupled effect of thermal softening and strain rate. Based on the calculated work hardening and thermal softening behaviors, a modified Johnson Cook (JC) model was developed to incorporate the coupled effects into the items of work hardening and thermal softening. Most of the average absolute relative errors ( AARE ) between the predicted and measured flow stresses were less than 5%. In addition, the prediction accuracy of the proposed constitutive model was further evaluated by a loading condition jump test. [ABSTRACT FROM AUTHOR]

This paper introduces a new ‘strength model’, named Split Johnson–Cook (SJC). The model is a generalization of classical Johnson–Cook (JC) and provides a much improved coherence for the plastic material description. Specifically, the new model tackles the issue that the effects of equivalent plastic strain rate and temperature shall not be taken as equal for each equivalent plastic strain, avoiding then heavy modeling errors on the lower yield stress and on the subsequent plastic flow. The salient features of the original JC model are shortly reviewed first, paying specific attention to possible modeling incoherencies. Two main shortcoming issues are framed and discussed. Further, a review on several modifications of the JC model from the literature is outlined. Then, the new SJC model is introduced in such a framework and thoroughly described. A comprehensive discussion on its calibration strategies follows, by developing three alternative calibration approaches. The new model is then applied to the material description of three real material cases (a structural steel, a commercially pure metal and a stainless steel), by considering literature sets of hardening functions recorded at different equivalent plastic strain rates and temperatures. SJC predicted trends are checked against experimental data, for each calibration strategy, by evaluating the material prediction on both lower yield stress and plastic flow. Obtained results are also compared to those provided by plain JC. The SJC model shows the capability to remarkably improve the material description, as compared to plain JC. Moreover, the fact of presenting a form very similar to that of the original JC model allows to possibly reusing some of the JC material parameters, which may be already known from available calibrations. Also, the SJC model keeps the same computational appeal of the original JC model and need of experimental data toward calibration, while heaviness of calibration and computational weight remain almost unchanged. [ABSTRACT FROM AUTHOR]

The uniaxial quasi-static and dynamic tensile tests were conducted at different strain rates (10 –3 s −1 , 800 s −1 , 1900 s −1 and 2900 s −1 ) for 7050-T7451 aluminum alloy. Then, research of the strain rate hardening coefficient in the original Johnson–Cook model at different strains and strain rates showed that the coefficient is a function of strain and strain rate from the tensile experimental results. Furthermore, a modified Johnson–Cook model was proposed to describe the flow behaviors of the studied alloy based on the correction to the strain rate hardening coefficient. Comparisons between the experimental data and predicted results using the original JC model, Khan–Liu (KL) model and the modified JC model showed that a better agreement can be obtained applying the modified model than the other two models. Verifications for predicting three new high strain rates (1500 s −1 , 2500 s −1 and 3500 s −1 ) experimental data demonstrated the modified JC model can provide an accurate description for the dynamic behaviors of the studied alloy. [ABSTRACT FROM AUTHOR]

A modified Johnson-Cook constitutive equation of Ti-6Al-4V alloy is proposed based on hot compression tests performed in the temperature range of 1073-1323 K and strain rate 0.001-1 s. The experimental stress-strain data were employed to develop the modified Johnson-Cook constitutive equation of different phase regimes (α + β and β phase). The predicted flow stresses using the developed equation were compared with experimental data. Correlation coefficient ( R) and average absolute relative error (AARE) were introduced to verify the validity of the constitutive equation. The values of R and AARE for α + β phase were 0.990 and 7.81%, respectively. And in β phase region, the values of R and AARE were 0.985 and 10.36%, respectively. Meanwhile, the accuracy, the number of material constants involved, and the computational time required of the constitutive equation were evaluated by comparing with a strain-compensated Arrhenius-type constitutive equation. The results indicate that accuracy of modified Johnson-Cook constitutive equation is higher than that of compensated Arrhenius-type model at α + β phase, while lower at single β phase region. Meanwhile, the time required for evaluating the material constants of modified Johnson-Cook constitutive equation is much shorter than that of the strain-compensated Arrhenius type ones. [ABSTRACT FROM AUTHOR]

Abstract: Constitutive model is very important in finite element simulation of Inconel 718 cutting process. However, there are few constitutive models for Inconel 718 which are suitable for the cutting process. In this research, firstly, dynamic behavior of Inconel 718 at high strain rate and elevated temperature of the same order as the practical cutting process was obtained using SHPB(Split Hopkinson Pressure Bar) test. In the tests, the strain rate was 5000–11000s−1, and the temperature was 500–800°C. Secondly, thermal and strain rate effect were discussed. Strain rate softening effect was found at high strain rate and discussed, and it was temperature dependent. Finally, a modified Johnson–Cook model was established. [Copyright &y& Elsevier]

Abstract: IC10 is a newly developed Ni3Al-based superalloy. In order to investigate the flow behaviors of IC10, tensile experiments were conducted over a wide range of temperatures (25–800°C) and strain rates (0.00001–0.01s) on Material Test System (MTS809). Experiments show that: (1) flow behaviors are not sensitive to strain rates at ambient temperature; (2) flow behaviors vary with the temperature at the same strain rate; (3) the yield stress varies little with temperature. In order to describe the flow features of IC10, the Johnson–Cook model is employed and modified. In Johnson–Cook model, strain rate effect and temperature effect are multiplied simply with hardening effect. In the equation, the coupling effect is omitted. By introducing a temperature effect function, Johnson–Cook model is modified and used to predict flow behaviors of IC10 under different experiment conditions. The results show that it is valid. [Copyright &y& Elsevier]

Uniaxial compression tests were conducted with strain rates in the range of 0.001–2000 s−1 at room temperature for transverse direction (TD) of AZ31 magnesium hot-rolled sheet alloy. The true stress-true strain curves were characterized by inflection points between convexity and concavity. The deformation mechanism of AZ31-TD was systematically discussed by combining Schmid Factor (SF), critical resolved shear stress (CRSS), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The results showed that the dominant mechanism of plastic deformation before inflection point of true stress-true strain curve was { 10 1 ‾ 2 } tension twinning, while the dominant mechanism of plastic deformation after inflection point was non-base slip. Based on the deformation mechanism of AZ31-TD analysis, a modified JC model was proposed to predict the true stress-true plastic strain curves of AZ31-TD magnesium hot-rolled sheet alloy, which agreed well with the measured curves. This solved the difficult problem of predicting the change of curve shape caused by tension twinning in the initial stage of plastic deformation. [ABSTRACT FROM AUTHOR]

In this study, the flow stress behavior of ferritic-pearlitic steel (C45E steel) is investigated through isothermal compression testing at different strain rates (1 s−1, 5 s−1, and 60 s−1) and temperatures ranging from 200 to 700 °C. The stress-strain curves obtained from experimental testing were post-processed to obtain true stress-true plastic strain curves. To fit the experimental data to well-known material models, Johnson-Cook (J-C) model was investigated and found to have a poor fit. Analysis of the flow stress as a function of temperature and strain rate showed that among other deformation mechanisms dynamic strain aging mechanism was active between the temperature range 200 and 400 °C for varying strain rates and J-C model is unable to capture this phenomenon. This lead to the need to modify the J-C model for the material under investigation. Therefore, the original J-C model parameters A, B and n are modified using the polynomial equation to capture its dependence on temperature and strain rate. The results show the ability of the modified J-C model to describe the flow behavior satisfactorily while dynamic strain aging was operative. [ABSTRACT FROM AUTHOR]