Johnson-Cook Damage Research Articles

Crystal plasticity finite element modeling and simulation of diamond cutting of polycrystalline copper

Microstructural-related deformation behavior leads to anisotropic machining characteristics of polycrystalline materials. In the present work, we develop a crystal plasticity finite element model of ultra-precision diamond cutting of polycrystalline copper, aiming to evaluate the influence of grain boundaries on the correlation between microscopic deformation behavior of the material and macroscopic machining results. The crystal plasticity dealing with the anisotropy of polycrystalline copper is implemented in a user subroutine (UMAT), and an efficient element deletion technique based on the Johnson-Cook damage model is adopted to describe material removal and chip formation. The effectiveness of as-established crystal plasticity finite element model is verified by experiments of nanoindentation, nanoscratching and in-situ diamond microcutting. Subsequent crystal plasticity finite element simulation of diamond cutting across a high angle grain boundary demonstrates significant anisotropic machining characteristics in terms of machined surface quality, chip profile and cutting force, due to heterogeneous plastic deformation behavior in the grain level.

Determining biaxial tensile stresses by fracture cruciform specimen at different temperatures and strain rates for Ti–6Al–4V alloy

Fracture loci of a ductile sheet metal, in some stress subspaces, can be predicted by determining the fracture stress points in the same subspace. This paper deals with determining the fracture stress points for Ti–6Al–4V alloy, under biaxial tension loading, at different temperatures and strain rates. For this purpose, biaxial tension of a fracture cruciform specimen was numerically simulated, using the ABAQUS software. In order to validate the finite element simulations, biaxial tensile fracture of an AA5083 cruciform specimen was numerically and experimentally studied. The material properties of AA5083 needed as the input data for simulations, were determined by performing experimental tests. Moreover, a dependent biaxial tensile mechanism was designed, manufactured and installed on an INSTRON-1343 uniaxial testing machine, to conduct the biaxial experimental tests. The numerical predictions for the location of fracture initiation, the path of fracture evolution and the force diagram in each of the specimen arms were compared with the experimental results. A good correlation was observed which confirms the validity of the finite element simulations. Then, the simulations were repeated for Ti–6Al–4V specimen. Hill1948 criterion was used to model the anisotropic plasticity, while Johnson–Cook damage model was incorporated to predict the fracture initiation and evolution path for different temperatures and strain rates. The results showed that the biaxial fracture stress points, corresponding to different displacement ratios, are mainly accumulated in the vicinity of equi-biaxial stress state. It can be concluded that, regardless of the anisotropy model, the fracture cruciform specimen cannot reveal a wide range of biaxial tension stress points.

A smooth particle hydrodynamic model for two-dimensional numerical simulation of Ti–6Al–4V serrated chip deformation based on TANH constitutive law

The saw-tooth chip formation is one of the main machining characteristics in cutting of titanium alloys. The numerical simulation of saw-tooth chip formation, however, is still not accurate, since most of these numerical simulation models are based on traditional finite element method, which have difficulties in handling extremely large deformation that always occurs in the cutting process. Furthermore, these models adopt the Johnson–Cook damage constitutive law that is implemented in commercial codes such as ABAQUS® and LS-DYNA® to describe the dynamic mechanical properties of material, but Johnson–Cook damage constitutive law cannot account for the material of behavior due to strain softening and the dynamic recrystallization mechanism that occurs in the cutting process of Ti–6Al–4. Therefore, this work introduces a material constitutive model named hyperbolic tangent (TANH) and an improved smooth particle hydrodynamics method, and then develops an improved cutting model for Ti–6Al–4V titanium alloy through our in-house code to predict saw-tooth chip morphology and cutting forces. When compared to the experiments and Johnson–Cook damage model, the improved cutting model better explains and predicts the shear localized saw-tooth chip deformation as well as cutting forces.

Determination of the Johnson-Cook damage parameter D4 by Charpy impact testing

Abstract This study proposes to design a road support structure subjected to high-strain-rate loading occurring during vehicle collisions. The strain-rate affects both the hardening process and the material failure process. For modeling the strain-rate influence on material, various mathematical material models are used including the Johnoson-Cook model. The main goal of the study is to presenta method for determining the parameters for the Johnson-Cook damage model, a hybrid method which requires Charpy impact tests on a standard specimen with an annular notch and a series of calculations using finite element method simulating the test. The advantages of the presented method compared to existing methods are the high availability of the equipment, simple and quick processing of results and significantly lower costs.

Determination of ductile damage behaviors of high strain rate compression deformation for Ti-6Al-4V alloy using experimental-numerical combined approach

Ductile damage behavior of Ti-6Al-4V alloy was characterized by the evolution of flow curves and deformed specimens in compression tests at high strain rates and various temperatures. Cracks along the shear bands of deformed specimens were observed at lower temperatures (20 °C and 100 °C) and high strain rates (2500–10,000 s−1). The failure initial strains (FIS) during crack generation were calculated according to the measured flow stresses at the transition from stable plastic to damage evolution stage. Special emphasis is placed on the influence of strain rate and temperature on the ductile failure initiation. The failure initiation parameters of Johnson-Cook (JC) damage model were obtained by genetic algorithm (GA) optimization using a combined experimental–numerical approach. That is, the ductile damage parameters were optimized according to the measured FIS and the simulated stress triaxiality, equivalent strains, stresses and temperatures, using compression simulation without damage model. At lower temperatures (T < 300 °C), the failure parameters were used to simulate the flow stresses and deformation of specimen by the JC plastic and damage models. To further validate the failure parameters, at higher temperatures (T ≥ 300 °C), a coupling modified JC (JCM) plastic and energy density based damage model was proposed to characterize the flow curves at damage evolution stage by compression simulation using a subroutine program. The predicted flow stresses and the deformed specimens were consistent with the experimental results.

Finite element analysis of AHS steel under dynamic loading using a micromechanical modelling

Currently, advanced high strength (AHS) steel sheets have been increasingly used in the automotive structural parts, where improved crashworthiness and lightweight design are required at the same time. Such steel sheets provide an excellent combination between high strength and great energy absorption. Most AHS steels exhibit microstructures containing several phases and constituents with different morphologies and mechanical properties. In this work, the dual phase (DP) steel grade 780 was investigated under dynamic tensile loading by means of a finite element modelling on the micro-scale. A representative volume element (RVE) model was applied to take into account the effects of microstructure characteristics on the mechanical behaviour of steel sheets at high strain rates. For the RVE modelling, the Johnson-Cook constitutive model was applied to describe the stress-strain response, whereas the Johnson-Cook damage model and damage locus were employed for predicting failure development of each individual phases of examined steel. The RVE simulations were performed under varying strain rates and states of stress and the results were subsequently compared.

An evaluation of fracture properties of type-304 austenitic stainless steel at high deformation rate using the small punch test

Among stainless steel, type-304 austenitic stainless steel is the most widely used because of high corrosion-resistance as well as favourable mechanical properties due to strain-induced martensitic transformation (SIMT). In order to utilize the application of type-304 austenitic stainless steel in dynamic loading condition, the fracture behaviours with the effect of the local distribution of SIMT in the bending deformation using a relatively small specimen need to be investigated. The effect of SIMT as well as thermal softening phenomenon at a high deformation rate has been examined insufficiently and mechanism for rate-sensitivity of fracture-mechanical characteristic is still unclear. In present study, experiment and FE simulations are performed for the SP test at different deflection rates for type-304 austenitic stainless steel. In order to describe the damage and fracture process of materials, a modified version of the Johnson–Cook damage model is applied. After confirming the validity of computation, the rate-sensitivity of fracture-mechanical characteristics of the steel is examined at room temperature. In addition, the effects of temperature and SIMT on the force-deflection curve and fracture properties are discussed to clarify the mechanism for an improvement of impact fracture-mechanical characteristics of the steel.

DETERMINATION OF MATERIAL RESPONSE AND OPTIMIZATION OF JOHNSON-COOK DAMAGE PARAMETERS OF ALUMINIUM 7075 ALLOY

The effects of rolling direction and notch radius on the mechanical response of aluminium 7075-T651 alloy were investigated and the Johnson-Cook damage parameters of aluminium 7075-T651 alloy on both rolling directions were determined. Specifically, mechanical responses of aluminium 7075-T651 along the rolling direction and perpendicular to the rolling direction were obtained from monotonic tensile tests. 56 tensile tests in total were performed on notched specimens with 3 different notch radiuses and smooth specimens. Tensile tests were repeated 7 times for each case to ensure the consistency and to obtain the closest mechanical response to the real mechanical response with minimum error. Experimental findings revealed that being perpendicular to the rolling direction deteriorates the elongation at failure dramatically but can increase the mechanical properties in elastic region. The final areas of the fractured samples, used for the calculation of Johnson-Cook damage parameters, were measured by an optical microscope. The Johnson-Cook damage parameters of aluminium 7075-T651 alloy for different applications were computed by Levenberg-Marquardt optimization method. Collectively, this study opens the venue for accurate damage simulations of aluminium 7075-T651 along the rolling direction and perpendicular to the rolling direction for different applications.

A New Experimental and Numerical Framework for Determining of Revised J-C Failure Parameters

Since damage evolutions of materials play important roles in simulations, such as ballistic impacts and collisions, a new experimental and numerical method is established to determine the revised Johnson–Cook (JC) failure parameters of a 2618 aluminum alloy and a Ti-6Al-4V titanium alloy. Not only the strain distributions, but also the stress triaxialities of designed specimens with different notches, are analyzed and revised using the finite element (FE) model. Results show that the largest strain concentrated on the surface of the circumferential area where the initial damage happened, which coincided with the practical damage evolution in the FE model. The complete damage strain, which denoted the largest strain before fracture calculated by the picture, is put forward to replace the traditional failure strain. Consequently, the digital image correlation (DIC) method and the micro speckle are carried out to measure the complete strain from the circumferential area. In addition, the relationships between the complete damage strain, the revised stress triaxiality, the strain rate and the temperature are established by conducting the quasi-static and dynamic experiments under different temperatures. Finally, the simulations for the ballistic impact tests are conducted to validate the accuracy of the parameters of the revised JC damage model.

Numerical Modelling and Optimization of Dry Orthogonal Turning of Al6061 T6 Alloy

In this paper, the influence of machining parameters, Cutting Speed, Feed Rate, and Depth of cut, on surface finish during dry orthogonal turning of Al 6061 – T6 alloy, is studied using the response surface methodology (RSM). This paper proposes a unique way to predict the surface finish in turning, using the effective plastic strain (PEEQ) values obtained from the simulations. A comprehensive finite element model was proposed to predict the surface finish accurately, by correlating the variance of the PEEQ. The Johnson-Cook damage model is used to define the damage criteria and Johnson-Cook material model is used to explain the material constitutive behavior. A dynamic, explicit method is used along with the Adaptive Lagrangian-Eulerian (ALE) method to predict material flow accurately. The influence of machining parameters was studied by assuming Central Composite Design (CCD). The output response, PEEQ, was fitted into analytical quadratic polynomial models using regression analysis, which shows that feed rate was the most dominant factor for PEEQ than the other parameters considered in this study. Using the individual desirability function method, the objective, optimal setting of the machining parameters was obtained for better surface finish.

Development of a simulation model to study tool loads in pcBN when machining AISI 316L

This paper presents the development of a FE-simulation model to predict the mechanical stresses and thermal loads that a cutting tool of polycrystalline cubic boron nitride (pcBN) is subjected to, when machining AISI 316L. The serrated chip formation of AISI 316L has a major impact on the periodic loads acting on the cutting tool. Therefore, it is vital to correctly model this serrated chip formation. One of the major difficulties with FE-simulations of metal cutting is that the extreme deformations in the workpiece material, often leads to a highly distorted mesh. This paper uses the Coupled Eulerian-Lagrangian (CEL) formulation in Abaqus/Explicit, where the workpiece is modelled with the Eulerian formulation and the cutting tool by the Lagrangian one. This CEL formulation enables to completely avoid mesh distortion. To capture the chip serration process, the workpiece material is described with the Johnson-Cook damage model. The FE-simulation results are validated via comparison of the modelled cutting forces, chip serration frequency, and contact length against experimental ones.

Numerical Modelling and Optimization of Surface Finish during Peripheral Milling of AISI 4340 Steel using RSM

The effect of machining parameters, Cutting Speed, Feed Rate, and Depth of cut, on surface finish during peripheral milling of AISI 4340 steel, studied using response surface methodology. This paper suggests a distinctive way to calculate the surface finish, using the variance of effective plastic strain values obtained from the numerical model. The Johnson-Cook damage and material models are used in the numerical model along with the ALE. The variance of PEEQ was optimized using ANOVA, which shows that cutting speed was the most dominant factor. The optimal settings of the machining parameters was obtained for better surface finish.\\

Effect of Variation of Johnson-Cook Parameters on Kinetic Energy and Simulation of 4340 Steel Projectile

Computer simulations have been used for decades in the modelling of high velocity impact and general large deformation problems. Several computer codes have been developed to simulate these types of problems under a variety of geometric conditions and for any variety of materials. The Johnson-Cook material model is widely used in the simulation of high velocity impacts and even penetration of target structures. This research work represents the study of effects of variation of Johnson-Cook material constants on ballistic impact and its effect on residual kinetic energy of projectile. In the Johnson-Cook damage model, there are five material constants viz. D1, D2, D3, D4 and D5, and it is very difficult to find out all of these material constants by experiments. The main objective of the present research is to determine the most sensitive parameter out of these constants. To accomplish this target, experimental testing was done and additionally the impact physics was likewise recreated numerically utilizing ABAQUS. For the impact phenomenon 4340 steel, 10 mm diameter projectile and a 1006 steel target plate were chosen. From this study, it is concluded that the most sensitive Johnson-Cook damage model constant is ‘D3’

Numerical simulation of two tool turning process

Double tool turning process is used to improve productivity. A 2D finite element model was developed using commercially available finite element analysis software Abaqus 6.13. The workpiece and the cutting tool materials are modelled as elasto-plastic and elastic material respectively. Johnson-Cook damage criterion was used for chip separation. The friction between the cutting tool and the workpiece is modelled based on penalty contact approach. The coefficient of friction between the chip and the first and second cutting tool was taken as 0.8 and 0.6 respectively. In this numerical investigation the effect tool separation distance over the cutting force, feed force and cutting temperature were studied. Three different tool separation distances were considered. The simulation result shows that cutting force and feed force of the front cutting tool and the rear cutting tool do not change appreciably with the variation of the tool separation distance. It was revealed that the temperature rise of the work material due to machining by two cutting tool is well below the recrystallization temperature. Hence the forces on front and rear cutting tool remain same for various tool separation distances. It was also observed that the cutting temperatures remained unchanged for the various tool separation distances.

Computational Investigation of Effects of Grain Size on Ballistic Performance of Copper

ABSTRACTNumerical simulations were conducted to compare ballistic performance and penetration mechanism of copper (Cu) with four representative grain sizes. Ballistic limit velocities for coarse-grained (CG) copper (grain size ≈ 90 µm), regular copper (grain size ≈ 30 µm), fine-grained (FG) copper (grain size ≈ 890 nm), and ultrafine-grained (UG) copper (grain size ≈ 200 nm) were determined for the first time through the simulations. It was found that the copper with reduced grain size would offer higher strength and better ductility, and therefore renders improved ballistic performance than the CG and regular copper. High speed impact and penetration behavior of the FG and UG copper was also compared with the CG coppers strengthened by nanotwinned (NT) regions. The comparison results showed the impact and penetration resistance of UG copper is comparable to the CG copper strengthened by NT regions with the minimum twin spacing. Therefore, besides the NT-strengthened copper, the single phase copper with nanoscale grain size could also be a strong candidate material for better ballistic protection. A computational modeling and simulation framework was proposed for this study, in which Johnson–Cook (JC) constitutive model is used to predict the plastic deformation of Cu; the JC damage model is to capture the penetration and fragmentation behavior of Cu; Bao–Wierzbicki (B-W) failure criterion defines the material's failure mechanisms; and temperature increase during this adiabatic penetration process is given by the Taylor–Quinney method.

A Computational Study of the Effects of Strain Hardening in Micro-asperity Friction Models

In this paper, we study the effects of plastic strain hardening and damage on the friction response of a surface at the microscopic and macroscopic scales. At the microscale, the role played by hardening and damage in the response of a single asperity is determined using three-dimensional finite element analysis. The sample materials for the asperity are Al 2024-T3 and Ti6Al4V, which are modeled as isotropic bilinear plastic and include Johnson–Cook damage. The friction responses for two different damage models (Johnson–Cook and Bao–Wierzbicki) are also compared for the perfectly plastic case. In the simulations the asperity is initially compressed in order to induce a normal preload and then sheared to study the friction response. Then a statistical homogenization approach is used to propagate these effects to the macroscale. Toward this end, the surface is modeled as an isotropic Gaussian random process. The computed microscale responses are parameterized, and the overall macroscopic response of the surface is determined. Results of this study show that, at the microscale, strain hardening increases the coefficient of friction, particularly at low interference values. Similarly, material response plays a significant role at the macroscale over a wide range of normal force values.

Quasi-static and high strain rate fracture behaviour of Ti6Al4V

Static and dynamic experiments on sheet and bar titanium Ti6Al4V alloy are presented. Aiming at a comprehensive set of data on the materials damage and failure properties, different sample geometries and loading modes are considered. For the Ti6Al4V sheet, tensile loading of in-plane shear, two different in-plane tensile and plane strain samples are used, for the bar, tensile loading of cylindrical samples and torsion of thin-walled tubes. High strain rates, up to 1500s−1, are achieved in split Hopkinson bar tensile and torsion setups. The evolution of the surface strain fields in the samples is obtained by a digital image correlation technique. Insight is gained in the underlying fracture mechanisms by post mortem evaluation of fracture strains, fracture surface morphologies and voids in the material adjacent to the fracture surfaces, using optical and SEM micrographs. Further analysis and interpretation of the test results is supported by finite element (FE) simulations which give valuable information on the stress and strain state at and in the vicinity of the fracture location, including the loading path up to the onset of fracture. In the FE simulations, strain rate and temperature dependent hardening is taken into account with the Johnson–Cook hardening law. Two models are used to describe the fracture behaviour of the Ti-alloy: for the sheet the phenomenological Johnson–Cook damage initiation criterion combined with an energy-based ductile damage law, for the bar a physically based Gurson-type failure model. Although, neither of the models is able to capture the full complexity of the fracture process, the FE simulations provide key information for an in-depth understanding of the fracture behaviour of Ti6Al4V.In all samples and test conditions, a ductile fracture is observed which is mainly affected by the stress triaxiality. At the lower triaxialities, the process of void nucleation and growth is abruptly ended by strain localization in narrow bands. The effect of strain rate is mainly felt through the induced thermal softening which favours strain localization.

Three-dimensional numerical modeling, simulation and experimental validation of milling of a thin-wall component

Study on mechanics of milling of thin-wall components using a helical end mill is important in view of its complex nature and prominent applications in aerospace, automobile and electronics areas. This article presents a realistic three-dimensional, thermo-structural, finite-element-based mathematical model for thin-wall milling of aerospace grade aluminum alloy. Lagrangian formulation with explicit solution scheme was employed to simulate the interaction between helical milling cutter and the workpiece. Behavior of the material at high strain, strain rate and temperature was defined by Johnson–Cook material constitutive model. Johnson–Cook damage law and friction law were used to account for chip separation and contact interaction. Experimental work was carried out to validate the results predicted by the mathematical model. The developed model predicted the forces in radial, feed and axial directions with errors of 14%, 26% and 33%, respectively. The prediction errors for deflections at top, middle and bottom portions of thin wall were within 11%–39%. The simulated chip dimensions were in good agreement with experimental results while the computed cutting temperature varied by 17% with respect to the experimental value. Overall, it was found that the developed model predicts the process responses with fair and acceptable prediction accuracy. Using the developed model, a study on the effect of process parameters on the performance parameters, namely cutting and thrust forces, stress distribution, cutting temperature, part deflection and chip morphology was carried out, which is not possible using a two-dimensional orthogonal or oblique cutting model. It was found that the developed three-dimensional mathematical model provided very useful insights into the complex physical interaction of helical cutting tool and workpiece during thin-wall milling of aerospace alloys.

Finite element and experimental analysis of machinability during machining of high-volume fraction SiCp/Al composites

The machinability, including machined surface, edge quality, and the distribution of the subsurface residual stress, was studied during the orthogonal cutting of high-volume fraction SiCp/Al composites by both finite element analysis and experiments. The effect of cutting parameters on surface roughness, sizes of edge breakout, and residual stress were investigated. The elastic-plastic constitutive model and Johnson–Cook damage model for the Al alloy matrix, and the elastic-brittle failure for SiC particle were implemented in the mechanical properties of composites during the cutting simulation. The results indicate that the surface morphology is primarily dependent on the fracture models of SiC particles, and the formation of the negative shear plain is the main reason of edge breakout. Due to the inhomogeneity in the composites, the distribution of surface and subsurface residual stress is not uniform, and the high residual stress was distributed in the interface between irregular particles and matrix. The average value of residual stress of SiC particle is similar to that of the matrix. The predicted machined surface morphology and edge breakout sizes correlated well with the experimental observation. This study highlights the important role of the fracture model of SiC particles on surface finish and the edge quality. It provides useful information for better understanding of the mechanics in machining of the SiCp/Al composites.

Experimental and numerical analyses of magnesium alloy hot workability

Abstract Due to their hexagonal crystal structure, magnesium alloys have relatively low workability at room temperature. In this study, the hot workability behavior of cast-extruded AZ31B magnesium alloy is studied through hot compression testing, numerical modeling and microstructural analyses. Hot deformation tests are performed at temperatures of 250 °C to 400 °C under strain rates of 0.01 to 1.0 s−1. Transmission electron microscopy is used to reveal the presence of dynamic recrystallization (DRX), dynamic recovery (DRY), cracks and shear bands. To predict plastic instabilities during hot compression tests of AZ31B magnesium alloy, the authors use Johnson–Cook damage model in a 3D finite element simulation. The optimal hot workability of magnesium alloy is found at a temperature (T) of 400 °C and strain rate ( e ˙ ) of 0.01 s−1. Stability is found at a lower strain rate, and instability is found at a higher strain rate.