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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]

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]

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]

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]

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]