Johnson-Cook Model Parameters Research Articles

Parameters of Holmquist–Johnson–Cook model for high-strength concrete-like materials under projectile impact

Holmquist–Johnson–Cook constitutive model has been widely used in analyzing the dynamic responses of concrete-like materials under projectile impact and explosive loadings, the constitutive parameters of which were always referred from the original documents and only applied to the normal strength concrete with the compressive strength of 48 MPa. Aiming to confirm the Holmquist–Johnson–Cook model parameters for high-strength concrete-like materials (compressive strength ≥60 MPa), based on the available test data from the quasi-static uniaxial compression, triaxial compression, Split-Hopkinson pressure bar, as well as the Hugoniot experiments, the strength parameters, the strain rate parameter, and the equation of state parameters of Holmquist–Johnson–Cook model for high-strength concrete-like materials are determined. Using the finite element program LS-DYNA, total eight sets of projectile penetration and perforation tests on high-strength concrete (uniaxial compressive strengths of 67.5–157 MPa) and high-strength rock targets (uniaxial compressive strengths of 60 and 154 MPa) are numerically simulated, respectively. By comparisons with the test data of penetration depths and residual velocities of the projectiles, the verifications of the proposed parameters are validated, which provides the reference for the design of protective structures.

Hemispherical nosed steel projectile high-speed penetration into aluminum target

Terminal ballistic performance of high-strength projectiles penetrating into metallic targets is mostly concerned by both weapon and armor designers. Most existing works are concentrated on the rigid-eroding penetration regime, and limited studies have addressed the rigid-deforming-eroding penetration regime. In this paper, nineteen shots of hemispherical nosed D6A steel projectiles penetration test on 5A06-H112 aluminum targets is conducted with a wide range of velocities (696m/s–1870m/s). The non-monotonic dependence of depth of penetration (DOP) on the impact velocity is observed, which successively corresponds to the three penetration stages, i.e., rigid projectile penetration, deforming projectile penetration without eroding and eroding projectile penetration. Then, for the non-monotonic rigid-deforming-eroding projectile penetration regime, the applicability of the existing six classical theoretical models for both rigid and eroding projectile penetrations is evaluated. Furthermore, the transition velocities (the upper limit of rigid penetration and the lower limit of eroding penetration) are discussed and an empirical judgement criterion for the occurrence of non-monotonic dependence is proposed. Finally, by conducting the dynamic compression test, quasi-static tension test under varying temperature, etc., the Johnson-Cook model parameters for the present target and projectile are calibrated and validated by numerically simulating the present test.

High-rate Deformation and Spall Fracture of Some Metals

An investigation of high-rate deformation and spall fracture of some metals in a wide range of strain rate was carried out by using the Kolsky method and plane-wave shock experiment. The dynamic stress-strain curves were obtained and speed dependences of the strength characteristics were constructed for commercially pure aluminum and copper, as well as for stainless steel. The strength limits and their dependences on the strain rate and temperature are determined. Based on the obtained mechanical characteristics, the parameters of Johnson-Cook model for stainless steel were determined with due allowance for the influence of the strain rate and temperature on the yield surface radius. It is noted that the time dependence of the spall strength weakly dependent on temperature. A rationale is offered that explains the results within the framework of Zhurkov's kinetic theory of strength.

Constitutive modeling for Ti-6Al-4V alloy machining based on the SHPB tests and simulation

A constitutive model is critical for the prediction accuracy of a metal cutting simulation. The highest strain rate involved in the cutting process can be in the range of 104–106 s–1. Flow stresses at high strain rates are close to that of cutting are difficult to test via experiments. Split Hopkinson compression bar (SHPB) technology is used to study the deformation behavior of Ti-6Al-4V alloy at strain rates of 10–4–104s–1. The Johnson Cook (JC) model was applied to characterize the flow stresses of the SHPB tests at various conditions. The parameters of the JC model are optimized by using a genetic algorithm technology. The JC plastic model and the energy density-based ductile failure criteria are adopted in the proposed SHPB finite element simulation model. The simulated flow stresses and the failure characteristics, such as the cracks along the adiabatic shear bands agree well with the experimental results. Afterwards, the SHPB simulation is used to simulate higher strain rate(approximately 3×104 s–1) conditions by minimizing the size of the specimen. The JC model parameters covering higher strain rate conditions which are close to the deformation condition in cutting were calculated based on the flow stresses obtained by using the SHPB tests (10–4–104 s–1) and simulation (up to 3×104 s–1). The cutting simulation using the constitutive parameters is validated by the measured forces and chip morphology. The constitutive model and parameters for high strain rate conditions that are identical to those of cutting were obtained based on the SHPB tests and simulation.

Determination and verification of Johnson–Cook model parameters at high-speed deformation of titanium alloys

Based on the available experimental data, dependences of true stress on true strain under dynamic loading for titanium alloys VT6, OT4, OT4-0 are constructed, and parameters for Johnson–Cook model are determined. Simulation results for deformation and fracture of fan case of aircraft engine at high-speed collision with the fan blade simulator in LS-DYNA software package are presented.

Determination of parameters of the Johnson-Cook model for the description of deformation and fracture of titanium alloys

Stress-strain curves of dynamic loading of VT6, OT4, and OT4-0 titanium-based alloys are constructed on the basis of experimental data, and the Johnson-Cook model parameters are determined. Results of LS-DYNA simulations of the processes of deformation and fracture of the fan casing after its high-velocity impact with a fan blade simulator are presented.

On the Selection of Johnson-cook Constitutive Model Parameters for Ti-6Al-4V Using Three Types of Numerical Models of Orthogonal Cutting

Abstract Johnson-Cook constitutive model is still the most used model in metal cutting simulation, although several drawbacks reported in the literature. A high number of Johnson-Cook model parameters can be found in the literature for the same work material. One question that may arise is “What is the most suitable set of Johnson-Cook model parameters for a given material?”. The present paper puts in evidence some issues related with the selection of these parameters from the literature. In this contribution, two sets of Johnson-Cook model parameters for Ti-6A-4 V are evaluated, using three types of metal cutting models. These models are based on three different formulations: Lagrangian, Arbitrary Eulerian-Lagrangian (ALE) and Couple Lagrangian-Eulerian (CEL). This evaluation is based on the comparison between measured and predicted chip geometry, chip compression ratio, forces, plastic deformation and temperature distributions.

Identification of Johnson–Cook and Tresca's Parameters for Numerical Modeling of AISI-304 Machining Processes

This paper presents a procedure for the identification of Johnson Cook model parameters and Tresca's law friction factor for orthogonal cutting of AISI 304. The process is described by a thermomechanical numerical model. The parameters are identified by minimizing the error in the prediction of cutting force, chip thickness, and chip curvature. Two optimization algorithms where tested: a pure Nelder–Mead method (NMM), and a hybrid procedure, in which the starting simplex for NMM is calculated by means of a genetic algorithm. The results emphasize the importance of the initial guess chosen in the optimization to obtain a reliable set of parameters. By using the optimized parameters in the numerical model, the cutting force, the chip thickness, and the chip curvature can be evaluated with an acceptable accuracy. The identified rheological and tribological coefficients are validated for different orthogonal cutting conditions.

Dynamic Tensile Behaviour and Full Field Strain Measurement of High Strength Steel

Uniaxial tensile tests were conducted on high strength steel 600 (HS600) in Split-Hopkinson Tension Bar at different strain rates in the range of 1100 to 3200s-1and in electromechanical universal testing machine at the strain rate of 1.1×10-3s-1. Digital image correlation was used together with high-speed photography to obtain full-field displacement and strain in the tensile specimens at dynamic strain rate tests. This high strength steel shows significant strain rate sensitivity. Based on the experimental results, the material parameters of Johnson-Cook model are determined. This model fits the experimental data well in the plastic zone.

Flow Stress Optimization for Machining Simulations

Flow stress is a vital input data for machining simulations, which is experimentally measured from Split Hopkinson pressure bar (SHPB) tests. However such flow stress does not fit machining conditions of strain, strain rate and temperatures and lead to serious simulation errors. In this research work an integrated Taguchi – Finite element (FE) methodology is adopted to optimize the flow stress of AISI 1045 steel material for orthogonal machining. The flow stress computed from the optimization approach along with thermo physical material properties are input into the FE code. The FE cutting forces and chip thickness ratio (CTR) showed an improvement of 6-8% and 2-4% over conventional Johnson – Cook (JC) models. An optimum set of JC model parameters were found from the study. The JC parametric analysis indicated high cutting force sensitivity to yield strength and CTR sensitivity to yield strength, strain hardening and thermal softening.

FEM on Constitutive Equation of High Strength Stress Steel GCr15

Accuracy of cutting simulation model mostly depends on whether its material constitutive equation describes workpiece physical property under cutting state. It is necessary to research on the constitutive properties of cutting material in the high strain state of temperature. In this paper high strength steel GCr15 is used as a research object under the high speed cutting state. By FEM Johnson-cook constitutive model in Hopkinson Experiment is simulated, and the sensitivity of constant on constitutive model is also analyzed. Also influence of temperature on workpiece material stress and strain is revealed. The result provides reference for Johnson-cook model parameters of high strength steel GCr15, and it provides theory basis of material properties analysis in cutting state as well.

Optimising flow stress input for machining simulations using Taguchi methodology

Flow stress is a vital input data for successful simulation of a machining process. However the flow stress data obtained from experiments do not represent the practical machining conditions which induce errors in the simulated output. In this research work the flow stress of Ti6Al4V titanium alloy is improved through a new integrated Taguchi – Finite element optimisation technique. The finite element (FE) outputs for cutting force, feed force and chip thickness ratio are compared with the results from the orthogonal machining process and an optimum set of material parameters of the Johnson – Cook (JC) flow stress equation is identified. The optimised flow stress is found to improve the simulated cutting forces by 3-16 %, feed forces by 2-25 %, chip thickness ratio by 0-19 % over flow stress computed from conventional JC model parameters. The yield strength parameter of the JC model impacts the simulation results the most and the JC material constitutive law is found to be robust in flow stress characterisation with the optimized parameters. (Received in March 2011, accepted in September 2011. This paper was with the authors 1 month for 1 revision.)

High-strain-rate behavior of maraging steel linear cellular alloys: Mechanical deformations

Abstract The high-strain-rate deformation response of 25% dense linear cellular alloy (LCA) structures made from high-strength high-toughness maraging 250 steel is investigated. Constitutive parameters for the Johnson–Cook strength model for this steel are determined and validated by correlating final and transient deformation states obtained from experiments on solid maraging 250 steel cylinders impacting a rigid high-strength steel anvil, with those predicted using AUTODYN-3D Lagrangian based finite element simulations. The constitutive parameters are then used to predict the deformation response of a 9-cell waffle-design LCA under axial impact against a rigid anvil. Experiments performed on the LCA structure under the same impact conditions reveal that the qualitative deformation response correlates well with simulations, indicating the unique response of the LCA structures is well captured by the validated Johnson–Cook model parameters.

Study on Calibration for Parameters of Johnson-Cook Constitutive Equation

Procedure of determination for parameters of Johnson-Cook model, which is widely used in numerical computation and design for manufacture process, is made. The paper describes fundamental investigation of Johnson-Cook constitutive equation firstly, then quasi-static compression experiment MTS is reviewed briefly, and dynamic compression experiment SHPB is studied from all aspects of experimental principle of one dimension stress wave, experimental measurement system to experimental data handling. In the end methods of Calibration for A, B, n, C and m of Johnson-Cook constitutive model’s parameters are discussed in details.

Study on the Dynamic Behaviors of X70 Pipeline Steel by Numerical Simulation

Using the commercial code ANSTS/LS-DYNA, this study has established a Split Hopkinson Pressure Bar (SHPB) finite element model (FEM) of X70 pipeline steel. Moreover, the stress-strain behavior of X70 pipeline steel has been investigated by a simplified Johnson-Cook model. The stress and strain relationship of X70 pipeline steel under different compact speeds is obtained under the high strain rate of 103S-1. The results obtained by numerical simulation agree well with those by experiments, and the parameters of Johnson-Cook model describe accurately the mechanical behaviors of X70 pipe line steel under high strain rate. This conclusion will serve as an important reference for developing and applying materials.