Papers by Keyword: Johnson-Cook Model

Abstract: This paper integrates a comprehensive overview of cylindrical shell simulations by means of finite element analysis, focusing on both ductile and brittle fracture behaviors under explosive loading. Special attention is given to high-carbon alloy steels that exhibit pronounced cleavage or quasi-brittle behavior and can produce smaller, higher-velocity fragments under certain conditions. We discuss key numerical approaches for fragmentation modeling and shrapnel kinetic energy calculations, and explore the relevant constitutive equations—particularly the Johnson-Cook law for high strain-rate plasticity and Linear Elastic Fracture Mechanics (LEFM) parameters for cleavage-type fracture. Emphasis is placed on microstructural factors (grain size, carbide distribution) that govern fracture and fragment mass distribution. We incorporate experimental findings on brittle fracture of steels under internal blast, highlighting how microcrack formation, alloy carbides, and high hardness can alter fragmentation and shell initial velocity.

Abstract: Cold spray technology is a solid-state deposition process where solid particles are accelerated to very high velocities by expanding a compressed gas through a supersonic nozzle. The particles impact a substrate located approximately 25 mm from the exit plane of the nozzle. Predicting the deformation and resultant properties helps in developing process parameters and tailoring coatings to get the desired properties. In this study, aluminum, copper, and nickel coatings were produced using a range of process parameters that produced different particle impact velocities. The Hollomon power law relationship and Johnson-Cook flow stress model were utilized to predict the hardness of cold spray coatings. Results showed there was good agreement between the predicted and measured hardness of the respective coatings. Additionally, a methodology was developed to measure deformation in the form of a flattening ratio of the deposited particles. There was good agreement between the predicted and measured flattening ratio, especially for the Al and Ni feedstock powders.

Abstract: High-speed cutting (HSC) is frequently adopted to manufacture parts in many industries, including aerospace and automotive. To manufacture high-quality parts, adiabatic shear banding (ASB), often observed on serrated chips of various metallic materials during the HSC process, should be suppressed and studied. ASB is formed due to work hardening of metallic materials and work softening induced by adiabatic heating. The onset of ASB during the orthogonal cutting of Ti6Al4V is modeled based on the continuum mechanics, taking both work hardening and work softening into considerations. The model is validated by finite element method (FEM) and experiments. Moreover, the ASB onset process is simulated in FEM to reveal the ASB formation mechanism. The effect of the mechanical properties of Ti6Al4V on the onset of ASB is investigated based on the Johnson-Cook model. The investigation reveals the main factors that affect the onset of ASB during the HSC process. Future work includes characterizing the mechanical behavior of Ti6Al4V after the onset of ASB during a cutting process by coupling the continuum mechanics and micromechanics.

Abstract: Polycrystalline diamond (PCD), is a tool material and widely used in nonferrous metal processing due to its excellent properties, such as high hardness, high wear resistance, high thermal conductivity and low friction coefficient. Considering the friction between the cutter and the workpiece, the heat generated by the elastic-plastic deformation and the heat transfer between the cutter and the workpiece. The finite element analysis software ABAQUS was used to study the effect of different processing parameters on the temperature field distribution and cutting force of the cutter, in the case of welded PCD double-edge end milling copper. The temperature distribution of cutting tools and the changing trend of cutting force with milling parameters was obtained. These technological parameters include the milling rotation speed n, the axial milling depth a_p, and the feed rate f. The simulation results show that the tool temperature increases with the increase of milling depth, feed per revolution and rotation speed. However, the tool temperature has little effect on the tool life. Under the condition of satisfying the work-piece surface quality and machining efficiency, low speed, small milling depth and small feed should be selected as far as possible. Milling depth has a great influence on cutting force. When milling speed is about 2400 r/min, the axial milling depth is 0.3 mm, and the feed is 0.2 mm/r, which can obtain small milling force and lower tool temperature, and further extend the life of PCD tool.

Abstract: This work compares the pure copper (T2 copper)’s stress-strain relationship at different strain rates in the uni-axial tension test and Split Hopkinson Pressure Bar (SHPB) test. Small samples were utilized in the high strain rate SHPB test in which the accuracy was modified by numerical simulation. The experimental results showed that the T2 copper’s yield strength at high strain rates largely outweighed the quasi static yield strength. The flow stress in the stress-strain curves at different strain rates appeared to be divergent and increased with the increase in strain rates, showing great strain strengthening and strain rate hardening effects. Metallographic observation showed that the microstructure of T2 copper changed from equiaxed grains to twins and the interaction between the dislocation slip zone grain boundary and twins promoted the super plasticity distortion in T2 copper.

Abstract: In high speed machining, to dynamically control the mechanical behaviour of the materials, it is essential to control temperature, stress and strain by appropriate speed, feed and depth of cut. In the present work, to predict the mechanical behaviour of Ti6Al4V and 316L steel bio-materials an explicit dynamic analysis with different cutting speeds was carried out. Orthogonal cutting of 316L steel and Ti6Al4V materials with 720 m/min, 900 m/min and 1200 m/min cutting speeds was performed, and the distribution of stress and temperature was investigated using Jonson-Cook material model. Additionally, the work aimed at determining the effect of cutting speed on work piece temperature, when cutting is carried out continuously. From the investigation, it was found that, while machining Ti6Al4V material, for the increase in cutting speed there was increase in tool-chip interface temperature. Specifically, this could found till the cutting speed 900 m/min. But, there was a decrease in tool-chip interface temperature for the increase in speed from 900 m/min to 1200 m/min. Similarly for 316L steel, the tool-chip interface temperature increased when increasing the cutting speed till 900 m/min. But reduction in temperature from 650 °C to 500 °C for steel and 1028 °C to 990 °C for Ti6Al4V were found, when the cutting speed increased from 900 m/min to 1200 m/min. The study can be used to conclude, at what temperature range the adoption of material with controlled shape and geometry is possible for potential applications like, prosthetic design and surgical instruments prior to fabrications.

Abstract: Aluminium sheet metal is nowadays used to fabricate lighter, crashworthy, fuel efficient and environment friendly vehicles. Ductile damage of sheet metals affects significantly the crashworthiness, as it naturally exhibits anisotropic behavior due to the grain orientation. Johnson-Cook (J-C) damage model is widely used in numerical simulation for assessing the failure modeling of crash component in particular at high strain rate. The Johnson-Cook material model available in literature is meant for isotropic material behavior which cannot be used directly for anisotropic behavior of materials. To characterize the plastic anisotropy of the rolled sheet, the modified Johnson-Cook material model should be developed. In this research the combination of experimental work and numerical analysis with clear and simpler calibration strategy for damage model is demonstrated. It aims to reduce laboratory tests using advanced numerical analysis to predict failure in order to save overall cost and development time.

Abstract: In this work experimental tensile tests were performed on a DP1000 steel at different temperature levels in the range (293-600) K. This experimental database was used for the identification of a Johnson-Cook constitutive model taking into account temperature effects. A critical void area fraction and a corresponding critical equivalent plastic strain were also identified from each temperature using a metallographic analysis previously described. This critical equivalent plastic strain was considered as a fracture criterion instead of the traditional fracture strain of the Johnson-Cook model and a corresponding damage parameter was determined in these specific conditions. Finally numerical simulations were carried out to analyze the influence of the temperature on the macroscopic critical fracture during a forming operation by bending.

Abstract: Microalloyed steels have been the subject of theoretical and experimental studies revealing their exceptional mechanical response under nonlinear deformation conditions. In microalloyed steels, especially in multiphase steels, the mechanical properties are adjusted by combination of microstructure components with different levels of theirs mechanical responses, including hardness and ductility. A comprehensive studies have revealed that a transition from the development of usual bulk dislocation microstructures to more architecture ones occurs when the applied strain path allows to cumulate the deformation energy what is also strictly connected with the chemical and structural compositions of analyzed materials. The study presented here aims at understanding the complex strengthening mechanisms as well as microstructure evolution and to provide a link with the mechanical behaviour of investigated steels under nonlinear deformation conditions. The proper choice of the work hardening model for the cyclic plastic deformation is essential for predicting the inhomogeneities occurring during metal forming. Aim of the current work is to discuss the differences between various hardening models with respect to their capabilities in capturing complex deformation models and possibilities of their direct application to finite element modelling of such deformation processes. The results of experimental studies are integrated with computer modelling and dislocation theory to provide insight into the unprecedented combination of properties achieved in certain multiphase steels such as ultra-high flow strengths, good ductility and workability. Finally, based upon results obtained in performed computer simulations, conclusions regarding the possibilities of potential application of the work hardening models in the identification process parameters, trough the inverse analysis, are drawn.

Abstract: The split Hopkinson pressure bar (SHPB) technique is widely-used to describe the impact compressive behavior of different materials including metals. During the impact test, the specimen deforms in a wide range of impact strain rate from 10² to 10⁴ s^-1. It is a reason why the method is studied for many years even though the structure of the apparatus based on the SHPB is simple. Actually, the cylindrical specimens are widely used for a compressive test and it is clearly seen that stress measured by the test includes the increment of stress (an error) derived by friction effect between a specimen and pressure bars. Therefore, it is important that the measured stress should indicate similar value as the proper stress of the material by reducing friction effect during not only quasi-static but also the impact test. Various attempts to reduce a friction effect in past have been conducted. A method to reduce friction effect is in general a use of lubricants. However, it is ineffective because it can be considered that this method contributes to an attenuation of the stress wave for obtaining the stress-strain curve under impact loading. Thus, rise time of waves obtained by the experiment becomes longer compared with a case not to use lubricants. Recently, a study can be found using a ring specimen, however, the determined thickness of the specimen is quite thin and it can be considered that a buckling effect cannot be vanished. In this study, a use of hollow specimen is suggested to solve the problem related to reduce the friction effect by decreasing a contact area between a specimen and pressure bars instead of a cylindrical specimen. The compressive experiments at various strain rates are conducted by using a hollow specimen.