Search Results (64)

This study presents a systematic investigation into the mechanical responses of two tungsten-based alloys—84W–11.2Ni–4.8Fe and 88W–8.4Ni–3.6Fe—fabricated via selective laser melting (SLM). Quasi-static compression tests using a universal testing machine and dynamic impact experiments employing a split Hopkinson pressure bar (SHPB) were conducted over a temperature range of 298–598 K and strain rates spanning from 1 × 10⁻³ s⁻¹ to 2.3 × 10³ s⁻¹. Both alloys exhibited significant strain-rate hardening and thermal softening effects. Based on the experimental data, a Johnson–Cook (J–C) constitutive model was established. The fidelity of the calibrated model for the 84W alloy was rigorously validated through pulsed X-ray radiography and static armor penetration tests. The SLM-fabricated 84W-shaped charge liner produced a well-collimated jet with a tip velocity of 5101.5 m/s and achieved a penetration depth of 87 mm into rolled homogeneous armor (RHA)-equivalent steel targets. Numerical simulations using the developed J–C model showed close agreement with experimental measurements, with a maximum discrepancy of only 9.19%, thereby confirming the predictive capability of the constitutive model. These results demonstrate that the proposed J–C model can reliably characterize the large-deformation behavior of SLM-processed 84W and 88W liners under the extreme thermomechanical conditions characteristic of shaped charge jet formation—namely high temperature, high pressure, and ultra-high strain rate. Collectively, this work establishes a foundational framework for the application of SLM technology to shaped charge liner design and provides a critical basis for further research into jet formation physics and penetration mechanics of tungsten-based alloys. Full article

To support vehicle crash simulation in lightweight automotive design, this study develops high-precision constitutive and fracture models for a giga casting Mg-7Al-1.5La-1Zn magnesium alloy. Through mechanical testing and microstructural analysis, the plastic hardening, strain-rate strengthening, and ductile fracture behaviors are systematically investigated. A weighted mixed hardening model combining the saturation-type Hockett–Sherby and unsaturated Swift models is established. To overcome the limitations of the classical Johnson–Cook (J-C) model in capturing strain rate–plastic strain coupling, a modified dynamic increase factor incorporating equivalent plastic strain is proposed. Comparative fitting with the Cowper–Symonds model confirms that the modified J-C model better captures the twinning deformation mechanism under high strain rates and achieves higher accuracy. Among three fracture models Johnson–Cook (J-C), Modified Mohr-Coulomb(MMC), and Damage Initiation and Evolution Model (DIEM), the MMC model, which incorporates both stress triaxiality and Lode angle, shows the best predictive performance, with an average accuracy of 86.46% for fracture displacement across the full stress range. Microstructural characterization reveals grain refinement and dispersed Al₁₁La₃ precipitates that improve grain boundary properties. The established parameter set and calibration methods provide a reliable reference for material card calibration in crash simulation of giga casting magnesium alloy body structures. Full article

Aerospace canopies require both high impact resistance and optical transparency for pilot safety and aerodynamic shielding. While polycarbonate (PC) and poly(methyl methacrylate) (PMMA) are widely utilized, their vulnerability to strain-rate-dependent failure during high-velocity bird strikes necessitates advanced reinforcement strategies. This study presents a multiscale computational framework for nanoparticle-reinforced PC nanocomposites. To circumvent the prohibitive computational costs of atomistic simulations, a novel Strain-Rate Dependent Micromechanics (SRDM) framework is proposed for silica-, alumina-, and zirconia-reinforced PC systems, integrating the Goldberg constitutive model with Halpin–Tsai micromechanics to generate rate-dependent stress–strain responses and calibrate Johnson–Cook (J-C) parameters for impact-scale simulations. Unlike conventional approaches relying on atomistic simulations or empirical fitting, the proposed framework directly links micromechanical nanocomposite modeling with finite element bird-strike simulations. Bird-strike analyses were performed in LS-DYNA on a generic fighter canopy model. The framework further incorporates literature-based optical transparency criteria considering nanoparticle size and refractive-index compatibility. Among the investigated nanofillers, silica-reinforced PC provided the most favorable response. At the most critical impact location, the maximum canopy deformation decreased from 118.6 mm for neat PC to 61.9 mm, corresponding to an approximately 48% reduction. Although the reinforced canopy exhibited a reduction in peak internal energy absorption from approximately 10 kJ to 5 kJ due to its increased stiffness and reduced plastic deformation, it provided improved deformation resistance and structural stability under impact loading. Overall, this work provides a computationally efficient framework for designing bird-strike-resistant transparent nanocomposite canopy structures using nanofiller systems previously reported in the literature to preserve optical transparency. Full article

Accurate numerical simulation of Cr20Ni80 alloy processing relies on reliable constitutive and failure models. This study employs a comprehensive experimental–numerical approach to calibrate and validate the Johnson–Cook (J-C) parameters of Cr20Ni80 alloy under varying stress states and strain rates. Quasi-static tensile tests on smooth and notched specimens, alongside dynamic Split Hopkinson Tension Bar (SHTB) tests (1000–3000 s⁻¹), were conducted. Pulse-shaping technology was employed, and dynamic force balance was verified to ensure the physical validity of the high-strain-rate data. The constitutive parameters ($A=621.02 \mathrm{MPa}, B=543.20 \mathrm{MPa}, n=0.4564, C=0.0141$) were determined based on true stress–strain responses. Theoretical analysis confirms that the thermal softening effect caused by adiabatic heating can be neglected. Furthermore, the failure parameters ($D_1=-0.4300,{ D}_2=2.6405,{ D}_3=-0.7055$) were calibrated to capture the stress triaxiality effects ($R^2=0.978$). The parameter $D_4$ was iteratively calibrated using SHTB data from the 1000 s⁻¹ and 3000 s⁻¹ test conditions and validated using SHTB data from the 2000 s⁻¹ test condition. The engineering stress–strain curves obtained from simulations using the calibrated parameters showed good agreement with experimental results, confirming the reliability of the calibrated parameters. Full article

This study presents a comparative assessment of the Johnson–Cook (J-C) and Ductile Damage (DD) material models, evaluating their capability to replicate the tensile behavior and fracture development in ductile metals. Numerical models of AL6063-T4 aluminium and A36 steel dog-bone specimens with two different thicknesses were developed in ABAQUS to assess force–displacement response, stress–strain characteristics, and crack evolution under quasi-static loading. Results showed that specimen thickness directly doubled load capacity, while both models captured the overall elastic and plastic behavior of the materials. A key finding is that the DD model provided yield stresses closely matching the reference material values, whereas the J-C model exhibited higher apparent yields due to its intrinsic strain-rate sensitivity. Differences in damage behavior were also pronounced: the DD model better reproduced the gradual, inclined fracture path in aluminium, while the J-C model more accurately captured the strong necking-localization response characteristic of steel. Comparisons with experimentally tested specimens further supported these fracture tendencies. By analysing both materials under identical conditions, this work highlights the relative strengths and limitations of the two fracture formulations. The originality of the study lies in its systematic comparison across materials and thicknesses, providing clear guidance for selecting appropriate constitutive models in structural and computational mechanics research. Full article

This study presents a systematic numerical investigation into the ballistic performance of 7A52/7A62 aluminum alloy laminated plates with varying configurations. The dynamic mechanical behavior of the base alloys, 7A52 and 7A62, was first characterized experimentally, and the corresponding Johnson-Cook (J-C) constitutive parameters were calibrated. Using the calibrated J-C model, a series of numerical simulations were performed on several structural configurations, including single-layer (7A52-A, 7A62-B), double-layer (AB, BA), and four-layer laminates (ABAB, BAAB, ABBA, BABA). The results demonstrate that four-layer laminates exhibit markedly better ballistic performance than monolithic and double-layer plates. Among them, the ABAB stacking sequence—arranged in an alternating soft–hard–soft–hard pattern—shows the optimal performance, yielding a residual projectile velocity of only 256 m/s. This represents an approximately 27% reduction compared to the monolithic high-strength 7A62 plate. The overall ranking of ballistic performance is as follows: ABAB > BAAB > ABBA > BABA. Energy-based analysis further indicates that multi-interface delamination, coupled with plastic deformation and damage evolution, improves the energy-absorption efficiency of the laminated plates and thus enhances their ballistic resistance. This study offers valuable guidance for the lightweight design of laminated 7XXX-series aluminum alloy protective plates. Full article

With the growing requirements for multi-particle process simulation, improving computational accuracy, efficiency, and scalability has become a critical challenge. This study generally focused on comprehensive analyses of existing numerical methods for simulating particle–substrate interactions in gas–thermal spraying (including gas–dynamic spraying processes), covering both single-particle and multi-particle models to develop practical recommendations for the optimization of modern coating spraying processes. First of all, this paper systematically analyzes the key limitations of current approaches, including their inability to handle high deformations effectively or high computational complexity and their insufficient accuracy in dynamic scenarios. A comparative evaluation of four numerical methods (Lagrangian, Arbitrary Lagrangian–Eulerian (ALE), Coupled Eulerian–Lagrangian (CEL), and Smoothed Particle Hydrodynamics (SPH)) revealed their strengths and weaknesses in modeling of real gas–thermal spraying processes. Furthermore, this study identifies the limitations of the widely used Johnson–Cook (JC) constitutive model under extreme conditions. The authors considered the Zerilli–Armstrong (ZA), Mechanical Threshold Stress (MTS), and Preston–Tonks–Wallace (PTW) models as more realistic alternatives to the Jonson–Cook model. Finally, comparative analyses of theoretical and realistic deformation and defect-generation processes in gas–thermal coatings emphasize the critical need for fundamental changes in the simulation strategy for modern gas–thermal spraying processes. Full article

The accurate modelling of material removal mechanisms in grinding processes requires precise constitutive equations describing dynamic material behaviour under extreme strain rates and large deformations. This study presents a novel methodology for optimising the Johnson–Cook (J–C) constitutive model parameters for micro-grinding applications, addressing the limitations of conventional mechanical testing at strain rates exceeding 10⁵ s⁻¹. The research employed single abrasive grain micro-cutting experiments using a diamond Vickers indenter on aluminium alloy 7075-T6 specimens. High-resolution topographic measurements (130 nm lateral resolution) were used to analyse the scratch geometry and lateral material displacement patterns. Ten modified J–C model variants (A1–A10) were systematically evaluated through finite element simulations, focusing on parameters governing plastic strengthening (B, n) and strain rate sensitivity (C). Quantitative non-conformity criteria assessed agreement between experimental and simulated results for cross-sectional areas and geometric shapes of material pile-ups and grooves. These criteria enable an objective evaluation by comparing the pile-up height (h), width (l), and horizontal distance to the peak (d). The results demonstrate that conventional J–C parameters from Hopkinson bar testing exhibit significant discrepancies in grinding conditions, with unrealistic stress values (17,000 MPa). The optimised model A3 (A = 473 MPa, B = 80 MPa, n = 0.5, C = 0.001) achieved superior convergence, reducing the non-conformity criteria to Σk_A = 0.46 and Σk_K = 1.16, compared to 0.88 and 1.67 for the baseline model. Strain mapping revealed deformation values from ε = 0.8 to ε = 11 in lateral pile-up regions, confirming the necessity of constitutive models describing material behaviour across wide strain ranges. The methodology successfully identified optimal parameter combinations, with convergence errors of 1–14% and 7–60% on the left and right scratch sides, respectively. The approach provides a cost-effective alternative to expensive dynamic testing methods, with applicability extending to other ductile materials in precision manufacturing. Full article

Burrs are a significant machining defect affecting the quality of precision parts, and tool eccentricity may substantially influence milling burrs. Using AISI 304 stainless steel as the workpiece material, a three-dimensional thermo-mechanical coupled model for slot milling was constructed based on an explicit dynamics model. Combining the Johnson–Cook (J-C) constitutive model with the J-C shear failure criterion, simulations were conducted to obtain burr dimensions, cutting temperature distributions, and cutting force waveforms under different tool eccentricity directions and magnitudes. Results: As the eccentricity increases, the temperature of the top burr rises, and both the width of the top burr and the thickness of the exit side burr significantly increase. Under simulated conditions, the width of the top burr in down milling side increased by up to 70%. The burr dimensions under different eccentricity directions can differ by approximately 40%. Groove milling experiments revealed similar burr shapes between experimental and simulated results. Furthermore, the simulated cutting force waveforms aligned with those in the literature, indicating the reliability of the simulation outcomes. Based on these findings, it can be concluded that tool eccentricity significantly affects the dimensions of top burrs and exit side burrs. The width of top burrs and the thickness of exit side burrs are positively correlated with the tool eccentricity distance, while exit bottom burrs remain unaffected by eccentricity. These research results provide valuable reference for burr suppression in practical machining operations. Full article

Temperature and strain rate play a crucial role in determining the mechanical properties of metals. These critical parameters are typically assessed using the split Hopkinson pressure bar (SHPB) test. However, previous studies have seldom considered the coupled influence of temperature and strain rate on dynamic mechanical behavior, thereby reducing the accuracy of constitutive models. To accurately characterize the dynamic mechanical behavior of 34CrNi3MoA low-alloy steel, a new constitutive model combining temperature and strain rate was developed. Firstly, SHPB experiments under varying temperatures and strain rates were designed to obtain actual stress–strain curves. The results indicate that the mechanical properties of 34CrNi3MoA low-alloy steel are significantly influenced by both temperature and strain rate. True stress has a significant temperature-softening effect within the temperature range of 25 °C to 600 °C, while the flow stress in the yield stage increases with rising strain rate. Secondly, a novel constitutive model was established by integrating a correction function. The model comprises three components: a strain rate-strengthening function influenced by temperature, a temperature-softening function influenced by strain rate, and a strain-hardening correction function accounting for the coupling of temperature and strain rate. Comparing the mean relative error, the new model significantly improves accuracy compared to the original Johnson–Cook (J-C) model. Full article

The aim of this study was to analyse in detail the effect of varying the parameters of the Johnson–Cook (JC) material model on the results of a numerical simulation of the orthogonal turning process of the Ti6Al4V titanium alloy. The first step involved an experimental study, including the recording of cutting force components and temperature, as well as the measurement of chip geometry, which was used to validate the FEM simulation. This was followed by a sensitivity analysis of the JC model with respect to five parameters, namely A, B, C, m, and n, each modified independently by ±20%. The effects of these changes on cutting forces, cutting zone temperature, stresses, and chip geometry were evaluated. The results showed that parameters A, B, and m had the greatest influence on the physical quantities analysed, while C and n are of secondary importance. The analysis highlighted the need for precise calibration of the JC model parameters, especially when modelling machining processes involving difficult-to-machine materials. The results provided practical guidance for optimising the selection of constitutive parameters in machining simulations. Full article

Aerospace and marine engineering impose higher requirements on mechanical properties and lightweight design of materials. In this work, combining the high mechanical properties of FeCrNi medium entropy alloy (MEA) and the lightweight advantages of lattice structure, four types of high-performance FeCrNi MEA lattice structures (BCC, BCCZ, FCC, and FCCZ) were prepared by selective laser melting (SLM) technology, and their dynamic mechanical properties were systematically characterized via split Hopkinson pressure bar (SHPB) method. The results demonstrate that the FCCZ FeCrNi MEA lattice structure exhibits superior comprehensive performance among the four lattice structures, achieving the highest specific compressive strength of 59.1 MPa·g⁻¹·cm⁻³ and specific energy absorption of 26.3 J/g, significantly outperforming conventional lattice materials including 316L and AlSi10Mg alloys. Furthermore, the finite element simulation and Johnson-Cook (J-C) constitutive model of the dynamic compression process can effectively predict the microstructural evolution and mechanical response of lattice structure, providing critical theoretical guidance for optimizing the design of high-performance lattice structure materials. Full article

In the context of Al-Kharj city, which is steadily advancing as an industrial and manufacturing hub within Saudi Arabia, this study has significant relevance. The city’s focus on metal forming, fabrication, and materials engineering makes it crucial to optimize processes such as hot deformation of metallic alloys for various sectors, including aerospace, automotive, oil and gas, and structural applications. By assessing and comparing phenomenological and physical material models for nickel, aluminum, titanium, and iron-based alloys, this study aids Al-Kharj industries in advancing their process simulation and predictive performance. Thus, this study aims to evaluate the proposed phenomenological and physically based constitutive models for Ni-, Al-, Ti-, and Fe-based alloys to enhance the accuracy of high-temperature deformation simulations. Phenomenological models investigated include the Johnson–Cook (JC), Fields and Backofen (FB), and Khan–Huang–Liang (KHL) formulations, while the Zerilli–Armstrong (ZA) model represents the physical category. Additionally, various modifications to these models are explored. Model parameters are calibrated using the Levenberg–Marquardt algorithm to minimize mean square error. Performance is assessed through key statistical metrics, including the correlation coefficient (R), average absolute relative error (AARE), and root mean square error (RMSE). Of the 32 models analyzed, a modified version of the JC model delivers the highest accuracy across all alloys. Furthermore, four other modifications, one each for the JC and ZA models and two for the FB model, exhibit superior predictive capability for specific alloys. This makes this study valuable not just academically, but also as a practical resource to boost Al-Kharj’s industrial competitiveness and innovation capacity. Full article

Owing to potential inaccuracies in the current stress–strain curve used for constructing the Johnson–Cook (JC) constitutive model of amorphous alloys, the parameters of the JC constitutive equation were derived using Oxley’s cutting theory, negative chamfer theoretical mechanics modelling, and the particle swarm optimisation algorithm. A two-dimensional finite element cutting model was subsequently established using AdvantEdge software. The optimised constitutive model was used to simulate the main cutting force (Fz) and the backward force (Fy), which resulted in average errors of 12.461% and 9.161%, respectively. Based on the optimised constitutive model in which the JC constitutive equation parameters were derived using Oxley’s method, the variations in temperature, strain rate, and stress in the deformation zone during the cutting process were analysed. The chip microstructures revealed the transformation of lamellar chips into serrated chips resulting from a combination of plastic deformation, adiabatic shear, and shear slip. Full article

This study developed a twinning-induced plasticity (TWIP) steel characterized by lightweight, high strength, and high toughness. Tensile tests were conducted at strain rates ranging from 10⁻⁴ to 6500 s⁻¹ using a universal testing machine and a Hopkinson bar to evaluate the material’s mechanical properties. A Johnson–Cook (J-C) constitutive model was developed based on the mechanical performance data for high-strain behavior. X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to analyze the microstructural evolution and fracture mechanisms of tensile specimens. The results show that the TWIP steel exhibits positive strain rate sensitivity (PSRS) under both quasi-static and dynamic strain rates. At high strain rates, the yield strength increased from 1133.0 MPa to 1430.6 MPa, and the tensile strength rose from 1494.3 MPa to 1640.34 MPa. The J-C model fits well at strain rates of 1000 s⁻¹ and 3000 s⁻¹, but fitting errors increase at higher strain rates due to the competition between thermal softening and strain hardening. XRD results reveal no significant phase transformation occurred during deformation, with twinning being the dominant mechanism. As the strain rate increased, deformation twins appeared in the material’s microstructure, inducing plastic deformation during tensile testing. The twin volume fraction increases progressively with the strain rate. At high strain rates, secondary twins emerge and intersect with primary twins, refining the grains through mutual interaction. The TWIP effect enhances the material’s mechanical performance by improving its strength and ductility while maintaining its lightweight nature. Full article