Johnson-Cook Strength Model Research Articles

Pore collapse, shear bands, and hotspots using atomistics-consistent continuum models for RDX (1,3,5-trinitro-1,3,5-triazinane): Comparison with molecular dynamics calculations

Shock-induced energy localization is a crucial mechanism for determining shock sensitivity of energetic materials (EMs). Hotspots, i.e., localized areas of elevated temperature, arise when shocks interact with defects (cracks, pores, and interfaces) in the EM microstructure. The ignition and growth of hotspots in a shocked energetic material contribute to rapid chemical reactions that can couple with the passing shock wave, potentially leading to a self-sustained detonation wave. Predictive models for shock-to-detonation transition must correctly capture hotspot dynamics, which demands high-fidelity material models for meso-scale calculations. In this work, we deploy atomistics-guided material models for the energetic crystal RDX (1,3,5-trinitro-1,3,5-triazinane) and perform tandem continuum and all-atom molecular dynamics (MD) simulations. The computational setup for the continuum and MD simulations are nearly identical. The material models used for the calculations are derived from MD data, particularly the equations of state, rate-dependent Johnson–Cook strength model, and pressure-dependent shear modulus and melting temperature. We show that a modified Johnson–Cook model that accounts for shear-induced localization at the pore surface is necessary to represent well—relative to MD as the ground truth—the inelastic response of the crystal under a range of shock conditions. A head-to-head comparison of continuum and atomistic calculations across several metrics of pore collapse and energy deposition demonstrates that the continuum calculations are in good overall agreement with MD. Therefore, this work provides improved RDX material models to perform physically accurate meso-scale simulations, to enhance understanding of hot spot formation, and to use meso-scale hot spot data to inform macro-scale shock simulations.

Uncovering the influence of mechanical properties on wave formation during high-velocity impact welding by numerical simulation

The formation of wavy interface is one of the distinctive features of high-velocity impact welding. It is known that the geometric parameters of waves (amplitude a and length λ) depend not only on the impact conditions, but also on the mechanical properties of the materials being welded. However, until now, the impact of mechanical properties on the formation of waves has only been explored in a limited number of studies. To address this issue, in this paper, we use extensively a numerical simulation. First, we demonstrate that the numerical model, in conjunction with the smooth particle hydrodynamics (SPH) solver, effectively replicates the outcomes of a carefully controlled high-velocity impact welding experiment. Secondly, based on the validated model, we conducted a systematic study of the influence of strength on the wave formation process. Using numerical simulations with Johnson-Cook and ideal elastic-plastic strength models, we show that various characteristics of strength have a profound influence on the wave formation process. Furthermore, it is crucial to consider not only the yield strength of a material, but also factors such as strain and strain-rate hardening, along with thermal softening, to fully understand the wave formation during high-velocity impact welding.

Milling of additively manufactured AlSi10Mg with microstructural porosity defects, finite element modeling and experimental analysis

Metal additive manufacturing finds its applications in various sectors, especially the automotive and aerospace industries, wherein weight reduction of components is of paramount importance with respect to performance and fuel consumption. However, additively manufactured metallic components usually undergo post-processing steps to make them ready for end use application. One of these steps is finish machining that is employed to overcome the surface irregularities and poor tolerances produced as a result of additive manufacturing (AM). These finish machining processes involve turning, milling, drilling, reaming, or grinding. This paper presents a three-dimensional (3D) finite element (FE) model to simulate the chip formation during the milling of an AM aluminum alloy AlSi10Mg, while taking microstructural porosity defects into consideration. The material was chosen for its significance in the aerospace and automotive industries. The proposed numerical model was developed using ABAQUS™ and is capable of predicting the cutting forces during the milling of AM AlSi10Mg. The Johnson-Cook strength and fracture models were utilized to simulate the deformation mechanics of the workpiece material subjected to high strains, high strain rates, and high temperatures caused by machining. Two algorithms have been proposed and discussed to model the microstructural defects in the AM metal. Machining tests were performed on an AM AlSi10Mg specimen block to validate the proposed finite element model. To further demonstrate the capability of the proposed model in capturing the influence of porosity on cutting forces, a study has been conducted revolving around the impact of different pore sizes. The chips produced during the machining tests were also collected to compare the morphologies between the numerically simulated chips and the ones obtained experimentally, to further strengthen the validity of the proposed model.

Parametric study in analysing the effect of spinning on the deformable projectiles undergoing impact

Projectiles spin as they move through the air due to the rifled barrels. The projectile consists of both translational and rotational velocities called spinning when the projectile reaches the target. In this parametric study dealing with influencing factors such as residual velocity, residual mass, residual energy etc. in analysing the effect of spinning on deformable projectiles undergoing impact are carried out based on the Finite Element Analysis (FEA) using commercial LS-DYNA software. The projectile and the target materials are considered deformable and modelled based on Johnson-Cook (JC) strength and failure models. Initially, the model is validated by using the experimental results available in the literature. The validated model is extended to study the effect of above cited parameters including projectile materials and target obliquity etc. on projectile spinning. In the present research, steel and lead materials are considered for the projectile. Al 7075-T651 material is considered for the target. The residual energy which is a function of residual mass and residual velocity has been computed for the projectile with different materials. It has been found that the projectiles made up of lead experienced more damage with the spin compared to steel. Accordingly, the lead material is not suitable for the projectile with spinning. Hence, the subsequent analysis is extended with the projectile made up of steel only and allowed to impact the target with different orientations. It has been observed that the projectile path is slightly deviating when it is impacted on an inclined target compared to normal impact conditions. So, the energy required to defeat the target with spin and without spin is evaluated to understand the spinning effectiveness. Based on the results obtained, it can be concluded that, for 90° target inclination, 1x spin is favourable compared to without spin that is, 0x. As the target inclination is decreased further, 2x spin is preferred compared to no spinning.

Strain-rate response of 3D printed 17-4PH stainless steel manufactured via selective laser melting

This research work aims at investigating the strain rate effects on the 17-4PH stainless steel produced by Selective Laser Melting (SLM), with the final goal of adding knowledge about its mechanical performance for applications under certain dynamic conditions. Mechanical characterization of 3D-printed samples was performed using a universal quasi-static electro-mechanical machine, a hydro-pneumatic machines, and a split Hopkinson Tensile Bar device for quasi-static, intermediate (5 s−1) and high strain-rates (100 s−1 and 300 s−1), respectively. The use of this technology represents the most interesting breakthrough of the paper, allowing to identify and to evaluate the performance of 3D-printed metals in relation to impacts or other dynamic conditions typical of different areas of engineering, which are impossible to be obtained by other technologies. The conducted tests allowed to identify the main information on the material behaviour, from the quasi-static to the high strain-rate regime, mainly in terms of stress–strain curves and fracture, and the behaviour after fracture was assessed by applying the Bridgman equations.The effect of horizontal and vertical printing directions, as well as of an annealing heat treatment, are also discussed. According to the evaluation of the main mechanical parameters, the strain-rate increase affects the mechanical behaviour both in the horizontal and vertical directions: samples built horizontally show increased yield stress and ultimate strain and decreased ultimate strain, whereas specimens printed vertically exhibit a remarkable increase in yield stress and a decrease of the ultimate stresses and strains. However, the better behaviour observed, with respect to the horizontally printed specimens, for vertically printed specimens in the quasi-static regime was no longer observed for intermediate and high strain rates. Moreover, all heat-treated specimens present higher strain-rate sensitivity than not heat-treated ones.Finally, the applicability of the existing Johnson-Cook material strength model to represent the mechanical behavior of 3D printed 17-4PH stainless steel is examined. The obtained results represent an important contribution to the current literature, because the dynamic behaviour of 17-4PH stainless steel produced by SLM, under the studied strain rates values, have been scarcely investigated so far.

Multi-Layer Fabric Composites Combined with Non-Newtonian Shear Thickening in Ballistic Protection-Hybrid Numerical Methods and Ballistic Tests.

Multi-layer fabrics are commonly used in ballistics shields with a lower bulletproof class to protect against pistol and revolver bullets. In order to additionally limit the dynamic deflection of the samples, layers reinforced with additional materials, including non-Newtonian fluids compacted by shear, are additionally used. Performing a wide range of tests in each case can be very problematic; therefore, there are many calculation methods that allow, with better or worse results, mapping of the behavior of the material in the case of impact loads. The search for simplified methods is very important in order to simplify the complexity of numerical fabric models while maintaining the accuracy of the results obtained. In this article, multi-layer composites were tested. Two samples were included in the elements subjected to shelling. In the first sample, the outer layers consisted of aramid fabrics in a laminate with a thermoplastic polymer matrix. The middle layer contained a non-Newtonian shear-thickening fluid enclosed in hexagonal (honeycomb) cells. The fluid was produced using polypropylene glycol and colloidal silica powder with a diameter of 14 µm in the proportions of 60/40. The backing plate was made using a 12-layer composite made of Twaron® para-aramid fabrics with a DCPD matrix-not yet used in a wide range of ballistics. Then, numerical simulations were carried out in the Abaqus/Explicit dynamic analysis. The Johnson-Cook constitutive strength model was used to describe the behavior of elastic-plastic materials constituting the elements of the projectiles. For the non-Newtonian fluid, a Up-Us EOS was used. The inner layers of the fabric were treated as an orthotropic material. Complete homogenization of the sample layers was carried out, thanks to which each layer was treated as a homogeneous continuum. As a parameter of fracture mechanics for shield components, the strain criterion was used with the smooth particles hydrodynamics method (SPH). Then, the results of simulations were compared with the results of the ballistic test for both samples placed next to each other, which resulted in the formation of a multi-layer composite in one ballistic test subjected to impact loads during firing with a 9 × 19 mm Parabellum FMJ projectile with an initial velocity of 370 ± 10 m/s. The results of numerical tests are very similar to the ballistic tests, which indicates the correct mapping of the process and the correct conduct of layer homogenization. The applied proportions of the components in the non-Newtonian fluid allowed a reduction in the deflection compared to previous studies. Additionally, the proposal to use a DCPD matrix allowed to obtain a much lower deflection value compared to other materials, which is a novelty in the field of production of ballistic shields.

Computational and experimental studies of penetration resistance of Ceramic-Metal composites

Study of penetration resistance of combinations of different types of materials has important application in design of body armours, vehicle armours, protection from landmines, etc. We report the development of indigenous Material Point Method (MPM3D) and Smoothed Particle Hydrodynamics (SPH3D) codes along with appropriate material strength and failure models and their validation against published results for different impact velocities. Mie-Gruneisen equation of state, Johnson-Cook strength and Johnson-Cook failure models are used for metals. Johnson-Holmquist model is used for ceramics. Comparison and strengths of these codes are discussed. Simulations are also performed independently for indigenous experiments to study the ballistic limit of three targets, viz. (i) Al-6061 plate (ii) Ceramic plate (iii) Ceramic backed by Al, upon impact by a flat nosed steel-4340 projectile accelerated to desired velocities using an electromagnetic coil gun. The residual velocities for given impact velocities are compared. Simulations carried out using commercial FEM software are also reported. The simulation and experimental results agree very well within 3%. Ballistic limit enhances greatly when ceramic plate is used along with Al plate.

Computational modeling of composite armour and effect of CNT inclusion using orthotropic material model

We report development of indigenous Material Point Method (MPM3D) and Smoothed Particle Hydrodynamics (SPH3D) codes for modeling and design of composite body armour. Typical armour consists of a ceramic backed by a polymer matrix composite. The ceramic plate contributes to blunting of bullet nose, its erosion and reduction in speed. The polymer matrix with high tensile strength arrests the bullet. Mie-Gruneisen EOS, Johnson-Cook strength and failure models were used for projectile. Johnson-Holmquist (JH2) model was used for ceramics. An orthotropic model which accounts for different compression and tensile properties in through-thickness and in-plane directions was implemented and used for Ultrahigh Molecular Weight Polyethylene (henceforth termed as ‘PE’). The codes were validated against published results for impact onto PE targets. Then the codes were used to simulate various published experiments (of coauthors) on ceramic/PE composite targets performed according to NIJ standards. Back Face deformation (BFS) is measured. In all cases, the projectiles do not penetrate through the armour panels, consistent with experiments. Typically, the SPH and MPM codes compute BFS values which only deviate within 10–20 % of measured values. The simulation results are also compared with the commercial FEM code simulations. Experiments and simulations were carried out for PE reinforced with Carbon Nanotube (CNT) inclusions. The mechanical moduli and other strength parameters of PE are adjusted to account for the increase in flexural strength due to inclusion of CNT. The CNT inclusion greatly reduces the BFS. The simulations results qualitatively follow these trends.

Study of dynamic mechanical behavior of 1060-H112 aluminum alloy: Experimental and numerical simulation

1060-H112 aluminum alloy with high ductility is widely used in industrial engineering. The study of its dynamic mechanical behavior has theoretical and engineering application value. In this paper, quasi-static tensile tests from room temperature to 250°C and high strain rate compression tests were conducted using a universal material testing machine and a Hopkinson compression bar. By using a hybrid test-numerical simulation method, a modified Johnson-Cook (MJC) strength model and Cockcroft-Latham (C-L) fracture criterion parameters were calibrated. Subsequently, Taylor impact tests were performed on 1060-H112 aluminum alloy specimens with a diameter of 12.66 mm and a length of 50.64 mm in the range of 176.3–483.03 m/s. Upsetting and tensile tearing were observed in the tests. A 12.68 mm diameter blunt nosed projectile impact test on 2 mm 1060-H112 aluminum alloy plate was also conducted with a light gas gun system, and the speed related parameters and failure modes were obtained. Finally, a three-dimensional model corresponding to the test was established in ABAQUS/Explicit finite element simulation software, and the failure modes of the Taylor rod and the velocity parameters and failure modes of the target impact test were predicted. The results show that the MJC strength model and the C-L fracture criterion can predict the experimental results of the two tests accurately. It shows that the MJC strength model and C-L fracture criterion have high accuracy, and they will play an important role in the application of 1060-H112 aluminum alloy in industrial engineering.

Effect of Unit Cell Height on the Ballistic Performance of the Body-Centered Lattice Structures

Lattice structures, produced by metal additive manufacturing technology, can be a potential alternative in armor applications, which are important parts of defense technologies due to their shock wave damping, energy absorption and light-weight properties. Despite the fact that the protection of metal lattice structures against explosives has been frequently investigated in the literature, their perforation performance is rarely studied. In this research, numerical ballistic penetration tests were carried out with Johnson-Cook strength and failure model parameters by using LS-DYNA software. AlSi10Mg alloy was chosen as a lattice material, which has high energy absorption ability. Both width and length were chosen as 4 mm for the body-centered lattice structure, while eight different cell height (3, 4, 5, 6, 7, 8, 9 and 15 mm) were used as unit cell parameters. The results show that the ballistic performance of lattice structures could be improved by optimizing the unit cell height for the body-centered lattice structures.

On the contact behavior of aluminum plate targets subjected to ogive nosed projectile impact

This study presents the effect of contact friction on the impact resistance of monolithic aluminum 1100-H12 plate targets against ogive nosed EN24 steel projectiles. The projectiles were propelled using a pneumatic air pressure gun against circumferentially clamped circular targets measuring 255 mm in diameter. The initial as well as residual velocities of the projectile were captured using a high-speed camera working at 10,000 fps. Finite element modelling of the ballistic impact was carried out using ABAQUS/Explicit module. Johnson-Cook strength and damage model was employed to model the flow and fracture characteristics of the target material, whereas, the projectile was modelled as a rigid body. The coefficient of tangential friction between the surfaces of projectile and target was varied and its influence on the deformation and the failure of the targets was investigated. The ballistic performance of the aluminum targets was compared in terms of velocity drop, ballistic limit, local as well as global target deformations and energy absorption in the target.

Damage characteristics of semi-infinite aluminium targets subjected to normal and oblique projectile impact

The present study investigates the ballistic performance of 50 mm thick 7075-T651 aluminum target against 7.62 API projectile. The focus of this study is to understand the dissipation of total energy engendered by the projectile in impacting the plate target at 0 (normal), 30° and 60° obliquities. Further, the penetration mechanisms and local as well as global plastic deformations developed in the target and projectile were explored. The ballistic experiments on the targets were performed by employing a universal gun and the depth of penetration of the projectile in the target was observed. Three-dimensional computational modelling of projectile and target was carried out in ABAQUS/Explicit module. The material response of both projectile and target was described by the Johnson-Cook strength and damage model. The influence of projectile deformation on the impact resistance of targets was also studied. The plastic strain energy dissipation in the target as well as projectile was evaluated using the validated numerical results and discussed in terms of the damage evolution and local as well as global deformation modes developed in the target and projectile during the impact process.

Experimental and numerical study on the ballistic resistance of 6061-T651 aluminum alloy thin plates struck by different nose shapes of projectiles

The aim of the present paper is to study the effect of shapes of projectile nose on the ballistic resistance of 6061-T651 aluminum alloy thin plates, and to evaluate the effect of Lode angle dependent fracture criterion when predicting the ballistic resistance of 6061-T651 aluminum alloy thin plates struck by projectiles with different nose shapes through finite element (FE) simulations. To this end, the ballistic impact tests are firstly conducted using different nose shapes of projectiles. Ballistic limit velocities (BLVs) of different projectile-plate pairs considered are calculated by using initial versus residual velocity data obtained from the experiments. It can be found that the BLV of spherical projectile is the highest, followed by ogival-, blunt- and hemispherical-nosed projectiles. Subsequently, a 3D FE model corresponding to the test is built by ABAQUS/Explicit software and then they are adopted to predict the ballistic resistance of the plate. In these simulations modified Johnson-Cook (MJC) strength model accompanied with either the Lode angle independent and slightly modified Johnson-Cook (MJC) fracture criterion or the Lode angle dependent and modified Mohr-Coulomb (MMC) fracture criterion are adopted to describe plate material properties. Finally, the predicted ballistic resistance of the plates is compared with those observed in the experiments. The numerical predictions of the plate struck by different nose shapes of projectiles show that the BLV predicted by Lode angle dependent MMC fracture criterion is more accurate for spherical and ogival-nosed projectile, while the BLV predicted by Lode angle independent MJC fracture criterion is more accurate for blunt- and hemispherical-nosed projectile. In addition, the results show that the Lode angle's effect is related to the curvature radius of the nose shape of projectile, i.e., the Lode angle's effect decreases with the increase of the curvature radius.

Investigation of the explosive type on the high strain forming of OFHC copper tube

The paper computationally investigates the explosive forming of the oxygen-free high thermal conductivity (OFHC) copper tube subjected to five different explosives. To investigate the effect of explosive type on the formability of OFHC copper tube, commonly used explosives, including C-4, TNT, HMX, Comp-B, and PBXN, was compared by using the finite element method. To verify the developed finite element model (FEM), the explosive forming experiments were carried out by using C-4. In the simulations, Coupled-Eulerian-Lagrangian (CEL) method to model the large deformations, Jones-Wilkins-Lee (JWL) equations of state (EOS) to define the explosive properties and Johnson-Cook (J-C) strength and damage models to specify the metal’s mechanical behavior were utilized. Besides, Hillerborg’s fracture energy was calculated with the Charpy impact test results and given as input to the FEM. The results of FEM were compared and verified using the results of explosive forming tests considering the mesh density and friction coefficient. The simulations revealed that the explosive type affected both the final shape and also the strain rate of the copper tube. When the simulation results for C-4 was taken as reference, HMX and PBX-N increased the strain rate as 110%, roughly. However, Comp-B and TNT reduced the strain rate by nearly 10% and 22%, respectively. Also, the explosive type changed the final hardness of the metal. OFHC Copper had the lowest hardness (112.7 HV) when the simulations were conducted with TNT. In contrast, the highest hardness value (129.5 HV) was reached when HMX was used in the simulations. In addition, simulations put forth that Hillerborg’s fracture energy criteria could be used in the explosive simulations to predict the damage on the metals.

Energy dissipation characteristics of single curvature metallic shells subjected to ballistic impact

The impact resistance of single curvature semi-cylindrical shell targets of aluminum 1100-H12 was explored against hard steel cylindrical projectiles. Experimental as well as numerical investigations were carried out to observe the performance of shell targets against ogive, conical, blunt and hemispherical nosed projectiles. Effect of oblique impact was studied on the ballistic performance of the shell targets at 0 (normal), 15 and 30° obliquity. Further, the impact performance of 2 mm thick monolithic and in-contact layered targets of equivalent thickness was evaluated and compared. The projectiles were driven by a pneumatic air gun and the projectile flight path was captured with a high-speed camera. The experimental results obtained in terms of incidence and residual velocities, and deformation profile of the targets, were validated with the numerical analyses conducted in ABAQUS/Explicit solver. Johnson-Cook constitutive strength and damage material model was employed to simulate the deformation and damage evolution in the targets. The ballistic performance of both monolithic and layered targets impacted at oblique incidence, was compared in terms of ballistic limits, failure mechanisms, local and global plastic deformations and plastic strain energy absorbed in radial, circumferential, axial and shear deformation modes. The in-contact layered shell targets exhibited significantly higher impact resistance than the monolithic targets against all projectiles. Target configurations impacted at oblique incidence with conical and ogive nosed projectiles showed increase in global deformation, while, opposite behaviour was observed in case of blunt and hemispherical nosed projectiles. The plastic strain energy absorbed in various deformation modes correlated with the failure patterns observed in the target material during ballistic impact.

High strain-rate behaviour of as-cast and as-build Inconel 718 alloys at elevated temperatures

The restoration of Inconel 718 components through conventional processes typically require cost-intensive machining operations. Moreover, the refurbishment and reuse are extremely important in structural components likely to be subjected to harsh operating conditions (dynamic loads and elevated temperatures). That is why additive manufacturing processes are rising as disruptive techniques for the restoration of Inconel 718 components. However, a limited number of studies have evaluated the mechanical properties of this nickel-base superalloy in harsh conditions. The objective of this study is to evaluate the coupled effect of strain-rates (0.001, 200 and 800 s−1) and temperatures (20, 350 and 550 °C) on Inconel 718 additive manufactured samples produced by Direct Energy Deposition. A raw Inconel 718 material for the preparation of as-cast samples has been also investigated, and the mechanical results have been compared. The mechanical characterisation at high strain-rates has been performed through a SHTB equipped with a water-cooled induction heating system. Similar mechanical behaviour has been observed between samples realised with a power laser of 400 W and as-cast samples. A gradual decrease of the mechanical strengths is observed for increasing temperatures. The calibration of the Johnson-Cook strength model highlighted the necessity of using specific thermal softening values as a function of fixed strain-rate and temperature.

Crater shape as a possible record of the impact environment of metallic bodies: Effects of temperature, impact velocity and impactor density

Metallic bodies that were the cores of differentiated bodies are sources of iron meteorites and are considered to have formed early in the terrestrial planet region before migrating to the main asteroid belt. Surface temperatures and mutual collision velocities differ between the terrestrial planet region and the main asteroid belt. To investigate the dependence of crater shape on temperature, velocity and impactor density, we conducted impact experiments on room- and low-temperature iron meteorite and iron alloy targets (carbon steel SS400 and iron‑nickel alloy) with velocities of 0.8–7 km s−1. The projectiles were rock cylinders and metal spheres and cylinders. Oblique impact experiments were also conducted using stainless steel projectiles and SS400 steel targets which produced more prominent radial patterns downrange at room temperature than at low temperature. Crater diameters and depths were measured and compiled using non-dimensional parameter sets based on the π-group crater scaling relations. Two-dimensional numerical simulations were conducted using iSALE-2D code with the Johnson–Cook strength model. Both experimental and numerical results showed that the crater depth and diameter decreased with decreasing temperature, which strengthened the target, and with decreasing impact velocity. The decreasing tendency was more prominent for depth than for diameter, i.e., the depth/diameter ratio was smaller for the low temperature and low velocity conditions. The depth/diameter ratios of craters formed by rock projectiles were shallower than those of craters formed by metallic projectiles. Our results imply that the frequency distribution of the depth/diameter ratio for craters on the surface of metallic bodies may be used as a probe of the past impact environment of metallic bodies.

Towards joinability of thermal self-piercing riveting for AA7075-T6 aluminum alloy sheets under quasi-static loading conditions

The self-piercing riveting (SPR) owns more advantages of acquiring high joint strength for similar and dissimilar metal sheets than the traditional spot welding. However, the conventional SPR may not obtain good joint quality for AA7075-T6 aluminum alloy sheets due to its high strength and low ductility. Thereby, the possibility of self-piercing riveting under elevated temperatures improving the riveting quality and mechanical behavior has thus been raised as an interesting topic. In this paper, a modified thermal self-piercing riveting (T-SPR) technology for AA7075-T6 sheets was proposed based on the process that the substrate was firstly heated and conducted by the subsequent riveting and heat treatment process. The post-riveted quality and quasi-static mechanical behavior of T-SPR joints under designated temperatures were intrinsically investigated by quantifying the interlocking parameters and the single-lap shear test to assess the optimized riveting temperature. Subsequently, an improved Arcan test was employed to investigate the quasi-static mechanical behavior of cruciform joints under different loading conditions. The failure modes of cross-lap joints were analyzed in detail by combining the experiments and FE simulations coupled with Johnson-Cook (J-C) strength and damage models. The influences of loading angle and loading speed on the mechanical behavior of T-SPR joints were further discussed. The outcomes show that the joinability of T-SPR for AA7075-T6 aluminum alloys can be largely improved by increasing the riveting temperature to 400°C. The loading angle and loading speed also have a significant impact on the mechanical behaviors and failure modes of T-SPR joints under quasi-static loading conditions.

Experimental Development of Johnson–Cook Strength Model for Different Carbon Steel Grades and Application for Single‐Pass Hot Rolling

Johnson–Cook (JC) high‐temperature strength material models have been widely used in finite‐element analysis (FEA) to solve variety of hot rolling problems. Herein, the temperature‐ and strain rate‐related parameters of JC model are experimentally calibrated for eight different steel grades including SAE 1018 and SAE 1045, structural steels (ASTM A572‐60, ASTM A690, and ASTM A992), two V‐modified 1535/45 grades, and one automotive advanced high‐strength steel grade. Experimental data are obtained from tensile tests performed at strain rates from 0.001 to 20 s−1 and at temperatures between 900 and 1200 °C. A genetic algorithm approach is used to determine JC model parameters for different steel chemistries and to calculate the rolling pressure for a simple flat rolling process using both a common analytical formulation and a finite‐element model (FEM). A model for the effects of steel chemistry on the JC model parameters is also discussed.

Simulation of Fragmentation Characteristics of Projectile Jacket Made of Tungsten Alloy after Penetrating Metal Target Plate using SPH Method

A smooth particle hydrodynamics (SPH) model was used to simulate the fragmentation process of the jacket during penetrator with lateral efficiency (PELE) penetrating the metal target plate to study the fragmentation characteristics of PELE jacket made of tungsten alloy. The validity of the SPH model was verified by experimental results. Then the SPH model was used to simulate the jacket fragmentation under different impact velocity and thickness of target plate. The influence of impact velocity and thickness of target plate on the jacket fragmentation was obtained by analysing the mass distribution and quantity distribution of the fragments formed by the jacket. The results show that the dynamic fragmentation of tungsten alloy can be simulated effectively using the SPH model, Johnson-Cook strength model, maximum tensile stress failure criterion and stochastic failure model. When the thickness of target plate is fixed, the greater the impact velocity, the greater the pressure produced by the projectile impacting the target plate; with the increase of impact velocity, the mass of residual projectile decreases, the number of fragments formed by fragmentation of jacket increases linearly, and the average mass of fragments decreases exponentially. When the impact velocity is constant, the greater the thickness of the target plate, the longer the pressure duration by the projectile impacting the target plate; with the increase of the thickness of target plate, the mass of residual projectile decreases, the number of fragments formed by fragmentation of jacket increases linearly, and the average mass of fragments decreases exponentially. The numerical calculation model and research method adopted in this paper can be used to study the impact fragmentation of solid materials effectively.