Johnson-Cook Material Constitutive Model Research Articles

3D finite element simulation for tool temperature distribution and chip formation during drilling of Ti6Al4V alloy

A comprehensive 3D finite element simulation study has been conducted to investigate the tool temperature distribution along cutting edge and chip formation during drilling of Ti6Al4V alloy by using commercial finite element software Abaqus/Explicit. The Johnson–Cook material constitutive model and material failure criterion were implemented across the formulations to achieve the tool temperature and chip formation in the drilling process. The effect of different mesh sizes on simulation results was also analyzed. To assess and verify the accuracy of the simulation model, the corresponding experiment studies were carried out by measuring the thrust force, tool temperature, and chip morphology. Compared results show that the predicted thrust force, temperature distribution, and chip morphology are in good agreement with those tested from experiments. According to the combination of both simulations and experiments, it can be not only found the whole varying pattern of the thrust force but also reveal that the temperature decreases from drill center to outer corner along the primary cutting edge. In addition, it can provide a more detailed and profound knowledge about chip formation. All these are assumed to be recommendations for the optimization of tool geometry and drilling processing.

Research on Airflow Cooling Characteristics of Titanium Alloy Engine Blade Surface Machining

This paper studied the airflow cooling during blade surface processing and explained the applicable occasions of airflow cooling. The flat heat transfer model was used to study the characteristics of the cooling airflow during blade surface processing. The study of the model showed that the cooling coefficient of the airflow was affected by speed and pressure. Furthermore, the generation and strength of the autogenous cooling airflow were closely related to the physical properties of the grinding tool. In terms of processing heat generation, this paper used the Johnson‐Cook material constitutive model to calculate the residual heat on the surface of the processed blade, and the surface temperature rise was within a controllable range. For the airflow intensity generated by the high‐speed rotation of the tool, the airflow preset method was used to verify whether it meets the processing conditions.

Quantitative evaluation of the microjet velocity and cavitation erosion on a copper plate produced by a spherical cavity focused transducer at the high hydrostatic pressure

Cavitation erosion at the high hydrostatic pressure causes the equipment to operate abnormally for the huge economic losses. Few methods can quantitatively evaluate the cavitation erosion intensity. In order to solve this problem, the cavitation erosion on a copper plate was carried out in a spherical cavity focused transducer system at the hydrostatic pressure of 3, 6, and 10 MPa. Meanwhile, the corresponding cavitation threshold, the initial bubble radius, and the microjet velocity in the ultrasonic field are theoretically analyzed to determine the dimension and velocity of microjet based on the following hypotheses: (1) the influence of the coalescence on the bubble collapse is ignored; (2) the dimension of the microjet is equal to the largest bubble size without the influence of gravity and buoyancy. Using the Westervelt equation for the nonlinear wave propagation and the Johnson-Cook material constitutive model for the high strain rate, a microjet impact model of the multi-bubble cavitation was constructed. In addition, through the analogy with the indentation test, an inversion model was proposed to calculate the microjet velocity and the cavitation erosion intensity. The microjet geometric model was constructed from the dimension and velocity of the microjet. The continuous microjet impact was proposed according to the equivalent impact momentum and solved by the finite element method. The relative errors of the pit depth are 4.02%, 3.34%, and 1.84% at the hydrostatic pressure of 3, 6, and 10 MPa, respectively, and the relative error in the evolution of pit morphology is 7.33% at 10 MPa, which verified the reliability of the proposed models. Experimental and simulation results show that the higher the hydrostatic pressure, the greater the pit depth, pit diameter, the pit-to-microjet diameter ratio, and the cavitation erosion intensity, but the smaller the pit diameter-to-depth ratio. The cavitation erosion intensity becomes significant with the ongoing ultrasonic exposure. In addition, a comparison of the cavitation pit morphology in the microjet pulsed and continuous impact modes shows that the continuous impact mode is effective without the elastic deformation caused by the residual stress. Using the cavitation pit morphology at the different hydrostatic pressures, the microjet velocity can be estimated successfully and accurately in a certain range, whose corresponding errors at the lower and upper limit are 5.98% and 0.11% at 3 MPa, 6.62% and 9.14% at 6 MPa, 6.54% and 5.42% at 10 MPa, respectively. Our proposed models are valid only when the cavitation pit diameter-to-depth ratio is close to 1. Altogether, the cavitation erosion induced by multi-bubble collapses in the focal region of a focused transducer could be evaluated both experimentally and numerically. Using the cavitation pit morphology and the inversion model, the microjet velocity in a certain range could be estimated successfully with satisfactory accuracy.

Effect of vibration on machining and mechanical properties of AZ91 alloy during FSP: modeling and experiments

The objective of the research is to determine the effect of friction stir processing (FSP) parameters and vibration on the machining behavior of AZ91 alloy. The article displays the state of the art of AZ91 alloy machinability including chip formation, chip morphology, and cutting forces. In this method, the vibration was applied to the process line through the fixture under the workpiece during the FSP. The three-dimensional finite element (FE) modeling was applied for simulating the small-hole drilling process of AZ91 alloy. The large deformation of work and the chip formation in drilling process is realized by incorporating Johnson-Cook material constitutive model and material failure criterion. It was concluded that the microstructure from 150 (μm) for base metal was modified to 28 (μm) and 16 (μm) for FSP and FSVP samples, respectively. It has been indicated that mechanical properties increase as vibration applied during the FSP. The vibration improves adiabatic shearing and thus leads to more discontinuous chips. To enhance the mechanical and machining properties of processed zone the friction stir vibration process as an “easy to apply” FSP method is recommended for different industries.

A Finite Element Modeling Prediction in High Precision Milling Process of Aluminum 6082-T6

This study investigates micro-end-milling machining prediction using three-dimensional finite element modeling method. The FE model was developed for contouring up-milling operation for prediction of chip flow, burr formation, cutting temperature and cutting forces in an integrated model. The flow stress behavior of the workpiece was modeled by the Johnson–Cook material constitutive model. Different cutting conditions were simulated to consider the effect of the process variables that might be difficult or impossible to follow in the physical experiments at this scale. The tool was precisely 3D modeled to describe the detailed geometry of the tool which is one of the critical aspects of the model and is characteristic of the cutter tool micro-geometry design. Furthermore, the tool deflection was studied using a FE model under the experimental cutting forces measured in the different cutting conditions in order to consider the micro-end-mill deviation from the nominal position. 3D simulations of chip flow and temperature distribution are compared in various cutting conditions. The results of the burr formation, temperature distribution and cutting forces in three directions predictions are compared against the experiments. Simulations were able to predict the burr height with an accuracy between 1 and 4 µm depending on cutting parameters settings. The results of this study are beneficial to comprehend the micro-end-milling chip and burr formation to increase the machinability of the workpiece and to understand the influence of cutting parameter in order to prevent several experimental tests prior to the final machining.

An improved material constitutive model considering temperature-dependent dynamic recrystallization for numerical analysis of Ti-6Al-4V alloy machining

Titanium alloys are well-known as hard-to-machine materials with a low thermal conductivity which gives rise to heat and thermal stress localization near the tool-chip interface during machining. The constitutive model that describes material behavior during severe deformation is fundamental to the fidelity of numerical simulations that offer a cost-effective method to study the machining process. However, the lack of understanding on the coupled temperature effects involved in the evolution of chip morphology, the constitutive model, which is essential for optimizing a machining process, is underexploited. This paper presents an improved Johnson-Cook material constitutive model (JCM-IM) to account the temperature-dependent factor, and its coupled effects between the critical strain and temperature on flow-softening of Ti-6Al-4V alloy during machining. Along with the procedure for implementing and calibrating the JCM-IM in a machining FEA software, the best-fit parametric values of the JCM-IM for characterizing orthogonal cutting of Ti-6Al-4V alloy are presented. The calibrated JCM-IM, which has been verified by comparing the simulated forces, chip morphology and overall/critical shear strains in the primary shear band over a wide range of cutting speeds and feed-rates, is capable of predicting different deformation mechanisms around the dynamic recrystallization onset temperature for machining of Ti-6Al-4V alloy. Several sets of simulation results, which agree well with experimental data, illustrate the effects of cutting speed on temperature distribution around friction/shear zones, chip morphology evolution, and shear strains in the primary shear zone. The numerical findings offer intuitive insights into the transition from a continuously smooth flow to a periodically serrated flow as the cutting speed increases.

FE modeling of burr size in high- speed micro-milling of Ti6Al4V

This article is focused on the finite element modeling of burr formation in high speed micromilling of Ti6Al4V. Studies show that the burr produced at the up milling side at the exit of the micromilling tool is the biggest among burrs at other locations. Therefore, side exit burr at the up milling side has been modeled through finite element modeling. Johnson cook material constitutive model has been implemented in the formulation of burr formation. Experimental work has been performed to validate the developed model. It is found that the burr height and width obtained from the simulation has been validated experimentally with a maximum error of 15%. It was found from the literature review that the cutting speed is the factor, which influences the burr formation. Therefore, the model has been further extended to study the effect of cutting speed on the burr size. A maximum tool rotation of 200,000rpm was considered with a tool diameter of 500μm. It is predicted from the simulation that, the burr size was reduced by 96% (both height and width) if cutting tool speed was increased from 10,000 to 200,000rpm. Therefore, it is concluded that the cutting speed is the major factor to reduce the burr size in micromilling of Ti6Al4V. This study shows that the high speed micromachining center can be helpful in producing the micro parts with less or no burrs. It is expected that further extension of the burr formation model can minimize the burr size to zero/near zero size.

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 simulation for Ti-6Al-4V alloy deformation near the exit of orthogonal cutting

Ti-6Al-4V alloy is known as a typical difficult-to-machine hard material due to its inherent properties such as low thermal conductivity, low elastic modulus, and high reactivity with cutting tool materials. This paper proposes a two-dimensional coupled thermo-mechanical model of plane strain orthogonal cutting for Ti-6Al-4V alloy deformation near the exit edge. Johnson–Cook material constitutive model and Cockroft–Latham damage criterion are utilized in the model for better understanding the plastic behavior and chips formation during the cutting process. The machining parameters such as cutting speed, tool edge radius, rake angle, and cutting depth are taken into account in the simulation. The results show that an edge defect generates at the exit edge after machining. The edge defect consists of two fracture surfaces, namely, the first fracture surface of opening-mode crack and the second fracture surface of sliding-mode crack. Besides, the edge defect sizes are greatly sensitive to machining parameters. This study provides a better understanding of burr/breakout formation mechanism near the exit surface and optimization of machining parameters in cutting Ti-6Al-4V alloy.

On the application of 3D finite element modeling for small-diameter hole drilling of AISI 1045 steel

This paper studies the three-dimensional finite element (FE) modeling for simulating the small-hole drilling process of AISI 1045 by using FE package Abaqus/Explicit. The large deformation of work and the chip formation in drilling process is realized by incorporating Johnson-Cook material constitutive model and material failure criterion. In order to verify the simulation model, the simulation and corresponding drilling tests are performed for the drilling process with 3-mm diameter solid carbide drills at several combination groups of rotational speeds and feed velocities. The estimated thrust force, torque and chip morphology from the simulation are in good agreement with those tested from experiments. The combination of both simulations and experiments not only reveals obvious varying pattern of thrust force, torque with the increasing of rotational speeds and feed velocities, which is consistent with the cutting theory, but also provides a more detailed and profound knowledge about the cutting mechanism including the contribution of chisel edge, drilling stage, and stress and strain distribution, which is assumed to be helpful for the optimization of the drill structure, geometry and drilling parameters.

Three-dimensional finite element modeling of high-speed end milling operations of Ti-6Al-4V

This article presents the development of a three-dimensional finite element model to simulate the high-speed end milling of Ti-6Al-4V titanium alloy based on the commercial finite element package Abaqus/Explicit. The Johnson–Cook material constitutive model was employed to model the flow stress behavior of the workpiece. Zorev’s friction model was used to determine the frictional behavior of the tool–chip interface, and Johnson–Cook shear failure criterion was used to realize chip separation. Based on the three-dimensional finite element model, cutting forces in three directions were predicted under different cutting conditions, and chip evolution and morphologies of different cutting parameters were also analyzed. Corresponding high-speed end milling tests were conducted, and cutting forces were measured using a piezoelectric dynamometer in order to validate the finite element model. The simulation results demonstrate an acceptable agreement with experimental results in both the chip morphologies and cutting forces in the range of cutting speed and feed rates considered.

High Strain Rate Tensile Behavior of Aluminum Alloy 7075 T651 and IS 2062 Mild Steel

Investigations on the effect of strain rate on tensile properties of two materials, namely, aluminum alloy 7075 T651 and IS 2062 mild steel, are presented. Experimental studies were carried out on tensile split Hopkinson pressure bar (SHPB) apparatus in the strain rate range of 54–164/s. Uncertainty analysis for the experimental results is presented. Johnson–Cook material constitutive model was applied to predict the tensile yield strength of the tested materials at different strain rates. It is observed that the tensile yield strength is enhanced compared with that at quasi-static loading. During tensile SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. An explanation to this is provided based on the increase in dislocation density and necking in the tested specimens during high strain rate loading and the consequent stress wave attenuation as it propagates within the specimen. The fracture behavior and effect of high strain rate testing on microstructure changes are examined. The peak force obtained based on strain gauge mounted on the transmitter bar is lower than the peak force obtained based on strain gauge mounted on the incident bar. There is an increase in tensile yield strength at high strain rate loading compared with that at quasi-static loading for both materials. The enhancement is more for IS 2062 mild steel than that for aluminum alloy 7075 T651. In the range of parameters considered, the strength enhancement factor was up to 1.3 for aluminum alloy 7075 T651 and it was up to 1.8 for IS 2062 mild steel. Generally, there was a good match between the experimental values and the Johnson–Cook model predictions.

Temperature Simulation in High-Speed Grinding by Using Deform-3D

Grinding is one of the most important operations in material processing. The study on grinding mechanism is difficult to carry out because of the difficulty in measuring the actual grinding temperature, stress and strain by experiments. Finite element analysis software Deform-3D is employed to create the Johnson-Cook material constitutive model for high-speed grinding simulation. Grinding model was constructed to reflect the temperature, strain and strain rate in the process of grinding 40Cr steel. The temperature of grinding area in simulation is analyzed to verify whether the finite element model is reasonable.

The Failure Investigations on the Thin Film Interface under the Dynamic Loading

The film spallation, a typical film / substrate failure style, could be caused by many reasons. The strong impact on the film/substrate can also lead to this failure phenomenon. So the film spallation induced by the strong impact is explored in this paper. Here the strong impact comes from the laser-driven flyer loading. In the numerical simulating process, the Finite Element Method (FEM) and Johnson-Cook material constitutive model have been used, moreover, some ideal film spallation results were got, which are helpful for us to understand this failure phenomenon.