Johnson-Cook Damage Research Articles

A reliable method for predicting serrated chip formation in high-speed cutting: analysis and experimental verification

Serrated chip formation influences almost every aspect of a high-speed cutting (HSC) process. This paper aims to develop a reliable method to accurately predict such chip formation processes. To this end, a systematic finite element analysis was carried out and a series of HSC experiments were conducted on a heat treated AISI 1045 steel. It was found that the integrative use of the Johnson–Cook thermal-viscoplastic constitutive equation, Johnson–Cook damage criterion for chip separation, and the modified Zorev’s friction model can precisely predict the serrated chip formation in HSC without artificial assumptions. This advancement has removed the major barrier in the current machining investigations by numerical simulation. The present study also found that the tool rake angle has a significant effect on serrated chip formation. As the rake angle increases, the chip sawtooth degree and cutting forces decrease, but the chip segmentation frequency increases.

Finite Element Simulation of Extremely High Speed Machining of Ti6Al4V Alloy

The finite element modeling and simulation of extremely high speed machining of Ti6Al4V alloy are presented in the paper. The Johnson-Cook’s constitutive model is used to describe the material behavior. The Johnson-Cook damage initiation criterion is used to predict the onset of damage due to void nucleation in ductile fracture. A damage evaluation law based on plastic strain energy and a fracture criterion combining the effect of different fracture mechanisms are proposed to model the progressive damage and fracture, respectively. Simulation results show that the predicted chip morphology agrees well with the experimental one. The distribution of temperature and specific cutting force are discussed later.

A fully coupled thermomechanical two-dimensional simulation model for orthogonal cutting: formulation and simulation

In this paper a fully coupled thermomechanical two-dimensional simulation model for orthogonal cutting is presented. The model is based on the arbitrary Lagrangian–Eulerian formulation with the remeshing technique. The material model used for the workpiece material includes Johnson–Cook plasticity, and as the chip separation criterion the Johnson–Cook damage law is employed. The different friction zones are modelled by the Coulomb friction law with a maximum limit for the friction. The capability of the model to represent the cutting process realistically is validated by performing simulations for different feed depths. The model is validated by comparison of the simulated values and measured experimental data for several different important process parameters, such as the feed force, the cutting force, the chip thickness ratio, the relative deformation widths, and the temperature distribution. The results from the simulations showed very good agreement with the experimental data.

Numerical Simulations of the Spall Damage of the Target Material Induced by Laser Driven Flyer Impacting

The spall phenomenon has been a subject of constant interest for many years, and it is still widely investigated in various ways including the experiment. This paper uses the method of smoothed particle hydrodynamics and the model of Johnson-Cook tensile cumulative damage to simulate the process of spall induced by the laser-driven flyer loading. Using this method, some numerical simulation results can be obtained, like the different time of the 2D image of damage distribution and the rear free surface velocity histories of target material. These results could offer some useful messages for the study on spall damage.

Modeling brittle–ductile failure transition with meshfree method

In this work, the element-free Galerkin (EFG) method is used to simulate the transition from brittle to ductile failure under finite deformation. A Galerkin formulation incorporating the Johnson–Cook damage model is implemented in numerical simulations. The constitutive update and the cracking method incorporated in the EFGM are described. Numerical simulations are compared with the experimental results performed by Kalthoff et al. They show that the proposed meshfree algorithm works well and it is confirmed that the proposed method provides a convenient and yet accurate means for study of failure transition.

Combined experimental and numerical approach for identification of dynamic material model parameters

Extraction of the material stress-strain curve from a dynamic tensile or shear experiment is not straightforward. Indeed, stress and strain are not homogeneously distributed in the specimen, and consequently no one-one relation exists between the measured elongation and strain on one hand, and the measured force and stress on the other hand. This work aims at improving the accuracy of the stress-strain curves calculated from high strain rate experiments and the modelling of the material behaviour. Therefore numerical simulations are used to determine the relationship between the average stress-strain and local effective stress-strain. The material model parameters used in these simulations are improved during an iterative procedure which combines the experimental results and the simulated stress and strain distribution. Stress triaxiality, local temperature and strain rate are taken into account. The method is applied to dynamic tensile and shear experiments on a Ti6Al4V alloy carried out on a split Hopkinson bar set up. The Johnson-Cook model is used to describe the strain rate and temperature dependent material behaviour. The two types of tests are used separately or simultaneously to extract and model the material behaviour. It is found that using tensile and shear experiments simultaneously has clear advantages. The same approach is used to identify parameters for the Johnson-Cook damage initiation criteria.

FEM INVESTIGATION FOR ORTHOGONAL CUTTING PROCESS WITH GROOVED TOOLS–TECHNICAL COMMUNICATION

Rigid-visco-plastic finite element models are used to simulate the chip formation and cracking in the turning processes with grooved tools. The Johnson-Cook constitutive equation and Johnson-Cook damage model, which are appropriate for high-speed machining, are assumed for the workpiece material properties. Thermal effects in cutting are considered. The tool material is considered as rigid, but heat-conducting, with the properties of tool material H11. The calculated chip back-flow angle, curling radius and thickness are analyzed as three typical chip shape parameters. The effects of land length and second rake angle of the grooved tool on chip formation, cracking and temperature are discussed. Some simulation results are compared with other published analytical and experimental results.

Investigation on the J-C ductile fracture parameters of 45 steel

In the FEM analysis of structure response under dynamic loading such as high velocity impact, the failure parameter is a important aspect of material behavior. With split Hopkinson tension bar tests and static material test at various stress states and temperatures, the effects of high strain rate, elevated temperature and stress triaxiality on the fracture behavior of 45 steel were studied. The Johnson-Cook damage fracture model parameters were exprimentally determined. The parameters were validated by comparison between the Taylor experiments and the simulations. The consistency between the experimental observation and numerical simulation indicates that the obtained parameters can describe the failure behavior of 45 steel under high speed deformation.

Evidence of Ductile Tearing Ahead of the Cutting Tool and Modeling the Energy Consumed in Material Separation in Micro-Cutting

Orthogonal cutting experiments using a quick-stop device are performed on Al2024-T3 and OFHC copper to study the chip–workpiece interface in a scanning electron microscope. Evidence of ductile tearing ahead of the tool at cutting speeds of 150m∕min has been found. A numerical finite element model is then developed to study the energy consumed in material separation in micro-cutting. The ductile fracture of Al2024-T3 in a complex stress state ahead of the tool is captured using a damage model. Chip formation is simulated via the use of a sacrificial layer and sequential elemental deletion in this layer. Element deletion is enforced when the accumulated damage exceeds a predetermined value. A Johnson–Cook damage model that is load history dependent and with strain-to-fracture dependent on stress, strain rate, and temperature is used to model the damage. The finite element model is validated using the cutting forces obtained from orthogonal micro-cutting experiments. Simulations are performed over a range of uncut chip thickness values. It is found that at lower uncut chip thickness values, the percentage of energy expended in material separation is higher than at higher uncut chip thicknesses. This work highlights the importance of the energy associated with material separation in the nonlinear scaling effect of specific cutting energy in micro-cutting.

Damage modeling for Taylor impact simulations

G. I. Taylor showed that dynamic material properties could be deduced from the impact of a projectile against a rigid boundary. The Taylor anvil test became very useful with the advent of numerical simulations and has been used to infer and/or to validate material constitutive constants. A new experimental facility has been developed to conduct Taylor anvil impacts to support validation of constitutive constants used in simulations. Typically, numerical simulations are conducted assuming 2-D cylindrical symmetry, but such computations cannot hope to capture the damage observed in higher velocity experiments. A computational study was initiated to examine the ability to simulate damage and subsequent deformation of the Taylor specimens. Three-dimensional simulations, using the Johnson-Cook damage model, were conducted with the nonlinear Eulerian wavecode CTH. The results of the simulations are compared to experimental deformations of 6061-T6 aluminum specimens as a function of impact velocity, and conclusions regarding the ability to simulate fracture and reproduce the observed deformations are summarized.

Meshfree simulations of thermo-mechanical ductile fracture

In this work, a meshfree method is used to simulate thermo-mechanical ductile fracture under finite deformation. A Galerkin meshfree formulation incorporating the Johnson-Cook damage model is implemented in numerical computations. We are interested in the simulation of thermo-mechanical effects on ductile fracture under large scale yielding. A rate form adiabatic split is proposed in the constitutive update. Meshfree techniques, such as the visibility criterion, are used to modify the particle connectivity based on evolving crack surface morphology. The numerical results have shown that the proposed meshfree algorithm works well, the meshfree crack adaptivity and re-interpolation procedure is versatile in numerical simulations, and it enables us to predict thermo-mechanical effects on ductile fracture.

A FEM study on mechanisms of discontinuous chip formation in hard machining

Chip types in machining are determined by the combined effects of workpiece material properties, cutting speed, and tool geometry. The understanding of chip formation plays an important role in machining process optimization and surface integrity. Discontinuous chips, one of the major chip types, are usually formed in hard machining at high speeds. In this study, a new method has been presented to simulate discontinuous chips in high-speed machining AISI 4340 (32 HRc). The workpiece material properties have been modeled using the Johnson–Cook (JC) plasticity model, and material crack formation and propagation simulated using the Johnson–Cook damage model. It has been shown that discontinuous chip is due to the internal crack initiation and propagation in front of the tool and above the cutting edge, rather than from the free surface. The simulated chip morphology correlated well with the experimental results.

Anisotropy-corrected MTS constitutive strength modeling in HY-100 steel

In this work, a microstructural-related model was developed to simulate micromachining of FCC polycrystalline copper. Indeed, a crystal plasticity framework was adopted to describe the anisotropy of the mechanical behavior. Some material microstructure characteristics (such as grain size, grain misorientation and crystallographic orientation) are explicitly considered through the constitutive model. For describing the material removal during chip formation, a modified thermodynamically consistent formulation of the Johnson-Cook damage model was used. The model was implemented in the ABAQUS/Explicit finite element solver with a user-defined subroutine, and the experimental validation was performed using data on the cutting forces available in the literature. Finally, the model was used to investigate the effect of the microstructure on the micro-machining cutting forces and chip formation process. According to the results, the proposed model allows capturing the cutting forces trends due to the crystallographic anisotropy.