Plastic Deformation Of Metals Research Articles

A modified Johnson–Cook model for the plastic behavior of metals in ultrasonic vibration-assisted upsetting processes

In this work, we present a constitutive description of the plastic behavior of the metals and alloys under Ultrasonic Vibration (UV). When UV is imposed, it induces a softening effect on the plastic deformation of metals and alloys, referred to as the acoustoplastic phenomenon. The volumetric softening mechanism of the acoustoplasticity must consider stress superposition and acoustic softening. Taking the Johnson–Cook (JC) constitutive model as the reference for metal thermo-plasticity, the flow stress reduction due to UV is introduced by three types of softening terms: subtractive, multiplicative, and coupled. Those different configurations will be quantified via physical and phenomenological assumptions. For the study and validation of the proposed constitutive models, we focus on a well-known material, 6063 aluminum alloy. The ultrasonic vibration is modeled by an assisted upsetting process of an aluminum billet and compared with experiments. The impact of variations of the strain rate, ultrasonic amplitude, and frequency on the softening behavior of the models are analyzed and compared with available experimental results. We find out that the subtractive and coupled models agreed well with the experimental results showing the errors ranging from 2.4–4.8% and 4.4%–8%, respectively. However, the predictive ability of the multiplicative model exhibits large discrepancies at the low stage of strains following the acceptable predictions at high stains. By understanding the impact of the UV on the acoustoplastic deformation of the metals and alloys we can establish a reliable theoretical framework for prospective numerical studies of the UV-assisted manufacturing processes which is the goal of the current research presented here.

Impact fatigue behavior of laser metal deposition 316L stainless steel with an automated impact fatigue system based on split Hopkinson bar technique

Repeated impact subjecting on the key components of equipment is always characterized by extremely high loading rate loading, while plastic deformation of most metals depends on loading rate. To ensure the reliability and security of these components, it is necessary to understand the loading rate effect on the fatigue performance. In this study, an automated impact fatigue system based on split Hopkinson bar technique was newly developed to investigate the materials’ impact fatigue behavior. Impact fatigue behavior and non-impact fatigue behavior of laser metal deposition 316L stainless steel were analyzed. The fatigue life decreases with the increasing loading rate, implying the significant loading rate dependence. The compression and fracture toughness tests combined with fractography analysis at high and low loading rates were also conducted to reveal the underlying mechanism of the difference between impact and non-impact fatigue life. Finally, microstructure of the laser metal deposition 316L stainless steel after impact and non-impact fatigue was characterized. It can be concluded that the fatigue crack is apt to initiate under impact fatigue due to the high density of dislocation entanglement, while under non-impact fatigue, a large number of twins are beneficial to delay the fatigue crack initiation.

Electric discharge process modelling when piston pins recovery in internal combustion engines

Introduction. The relevance of the topic of the presented article is determined by the improvement of the technology for repairing and restoring machine parts. Currently, the technology of restoring piston pins of internal combustion engines (ICE) by a high-energy method of plastic deformation of metal using the energy of a high-voltage pulse discharge in a liquid is widely used – the electrohydraulic effect, and on its basis electrohydraulic processing. The purpose of the article is to increase the efficiency of the method of restoring piston pins of internal combustion engines due to the use of the electrohydraulic distribution method.Materials and methods. The research methods such as the analysis of the degree of influence of the electrical parameters of the electrohydraulic distribution process on the amount of deformation of the piston fingers depending on the relevant material were used. The article discusses a mathematical model of the electric discharge process when restoring piston pins. The calculation method determines the modes and parameters of the process of electrohydraulic distribution of piston pins while maintaining their fatigue life, static strength and wear resistance.Results. In this work, the degree of influence of the electrical parameters of the electrohydraulic distribution process on the amount of deformation of the piston pins, depending on the product material used, is established. A mathematical model of the electric discharge process during the restoration of piston pins has been developed, and based on them, the modes and parameters of the process of electrohydraulic distribution of piston pins have been determined while maintaining their fatigue life, static strength and wear resistance.Discussion and conclusions. The studies have shown that exploding wires made of iron, copper, and tungsten are not effective in restoring piston pins with an internal radius of up to 10 mm. The pressure in the case of their use does not exceed 100 MPa. Exploding Al wires with a diameter of less than one millimeter have the greatest effect. In this case, the inductance of the circuit should be minimal, because this provides the largest share of the energy released in the discharge channel from all stored in the capacitor. This ensures the highest pressure in the channel. Based on the same considerations, the capacity should be limited to a range of 3-12 UF. This method can be applied to the restoration of other car parts.

Patterns of Grain Fragmentation During Plastic Deformation of Metals at Small to Medium Strains (Brief Review)

Patterns of Grain Fragmentation During Plastic Deformation of Metals at Small to Medium Strains (Brief Review)

Extended Gurson-Tvergaard-Needleman model considering damage behaviors under reverse loading

Void nucleation, growth, deformation and coalescence are the main microscopic damage mechanisms for plastic deformation of sheet metals. To describe the effect of reverse loading on the microscopic damage accumulation and ductile fracture, the damage evolution equations in regard of void nucleation, void growth, shear void nucleation and shear deformation damage were modified. Through the further introduction of the combined hardening model, an extended Gurson-Tvergaard-Needleman (GTN) model was constructed in this study, to improve the predictive ability of ductile fracture under reverse loading conditions. Two typical reverse loading experiments including compression-tension and shear-reverse shear were performed. The number, size and shape of microscopic voids were qualitatively analyzed and compared through the microscopic observations, it is indicated that the preloading and loading sequence strongly affect the damage accumulation and the final ductile fracture, which is the microscopic damage mechanisms under reverse loading. The proposed GTN model was verified by the load responses and displacements at fracture (DAFs) of the conducted reverse loading experiments. The good agreement between numerical simulations and experimental results proves the rationality of the proposed GTN model and its accuracy to the prediction of ductile fracture under reverse loading conditions.

Research on incremental forming simulation based on an improved constitutive model

The incremental sheet metal forming process, characterized by the step-by-step deformation of sheet metal using a simple die, is classified as a type of plastic deformation technology. This method allows for the formation of complex-shaped parts even without the use of a specialized die. Its notable characteristic lies in its low forming load and high flexibility. To accurately forecast finite element simulation outcomes for the incremental sheet forming of 2024-O aluminum alloy sheets, constructing a precise constitutive model is essential. Typically, the uniform strain range in traditional unidirectional tensile tests does not surpass 0.3, primarily due to the necking phenomenon. This limitation hampers the accurate prediction of the actual large plastic deformation process. To address this issue, a theoretical model describing the stress-strain relationship in metal plastic deformation processes is developed using crystal plasticity theory. The constitutive model for the forming of 2024-O aluminum alloy is then constructed by adjusting the hardening coefficient and hardening index. Utilizing the improved constitutive model, the incremental sheet forming process is simulated using ABAQUS software. Upon comparison with experimental results, it is observed that the Thickness Average Absolute Relative Errors (TAARE) of the adjusted constitutive model at forming angles of 60°, 55°, and 50° are 0.414%, 0.467%, and 0.256%, and The Thickness Root Mean Square Errors (TRMSE) are determined as 0.0121, 0.0116, and 0.0094, respectively. These results indicate that the constitutive model and parameters established in this study can adequately capture the mechanical behavior of 2024-O aluminum alloy during the incremental sheet forming process.

“Soft-hard” microstructure evolution and its relevance to high strength–plasticity and low plastic anisotropy of Al–Mg alloys based on ultra-fast heating

The mechanical anisotropy caused by the apparent texture after large plastic deformation and deformation strengthening in metals has always been a contradiction. Here, 80 % cold-rolled Al–Mg alloy was annealed using the ultra-fast heating process (500 °C/s heating to 450 °C), leading to substructured grains with high geometrically necessary dislocations (4.12 × 1014 m−2) and recrystallized grains with low geometrically necessary dislocations (0.78 × 1014 m−2); each of these accounted for approximately 50 % of the grains. The alloy's strength was much higher than the corresponding conventional annealing one, while the ductility remained unchanged. In addition, the weaker transition texture components such as Brass, Z, R-GossND, and Goss increased significantly due to the presence of many substructural grains. In contrast, the Cube texture decreased significantly, thus leading to a decrease in the texture intensity and, in turn, a significant reduction in the anisotropy. The excellent comprehensive properties are attributed to the microstructures with a mixture of “soft-hard” grains and multicomponent-low-intensity textures. The present study provides a new approach to fabricating Al–Mg alloys with high strength, high ductility, and a low anisotropy of the mechanical properties.

Intelligent Online Sensing of Defects Evolution in Metallic Materials during Plastic Deformation

Metallic plastic deformation involves complex microstructural changes and defect evolution, posing challenges in predicting and controlling the quality and performance of formed parts. Therefore, a pressing demand exists for a proficient online defect‐sensing system to monitor defects evolution continuously within components during plastic deformation in real time. This article proposes an intelligent online sensing approach for detecting defects in metallic plastic forming based on acoustic emission (AE) and machine learning. A comparative analysis is conducted on AE amplitude signals, stress–strain curves, and defect evolution during the tensile process of TA15 titanium alloy specimens under different stress states. It is found that the defect formation process can be divided into four stages based on the AE amplitude signals. A convolutional neural network model for intelligent defect sensing is established. It leverages transfer learning and is grounded in the relationship between AE signals and the evolution of internal defects. The prediction accuracy using different pretrained models is investigated and compared. It is discerned that utilizing GoogleNet as the pretrained model offers the swiftest training pace with a prediction accuracy of 97.57%. This approach enables intelligent online sensing of internal defect evolution in metal plastic deformation processes.

A dislocation-density-based crystal plasticity model for FCC nanocrystalline metals incorporating thermally-activated depinning from grain boundaries

A novel dislocation-density-based crystal plasticity model for nanocrystalline face-centered cubic metals is developed based on the thermally-activated mechanism of dislocations depinning from grain boundaries. Dislocations nucleated from grain boundary dislocation sources are assumed to be the primary carriers of plasticity in the nanocrystals. The evolution of the dislocation density thereby involves a competition between the nucleation of dislocations from grain boundary defect structures, such as ledges, and the absorption of dislocations into the grain boundary via diffusion processes. This model facilitates the simulation of plastic deformation in nanocrystalline metals, with consideration of the initial microstructure resulting from a particular processing method, to be computed as a direct result of dislocation-mediated plasticity only. The exclusion of grain boundary-mediated plasticity mechanisms in the formulation of the crystal plasticity model allows for the exploration of the fundamental role dislocations play in nanocrystalline plasticity. The combined effect of average grain size, grain size distribution shape, and initial dislocation density on the mechanical performance and strain-rate sensitivity are explored with the model. Further, the influence of the grain boundary diffusivity on post-yielding strain-hardening behavior is investigated to discern the impact that the choice of processing route has on the resulting deformation response of the material.

Triple junction disclinations in severely deformed Cu–0.4%Mg alloys

Stress fields arising from triple junction disclinations (TJDs) play a significant role in the microstructure evolution during the plastic deformation of metals. The calculation of TJD strengths from grain orientation data was developed by Bollmann more than 50 years ago, but so far applied only to collections of a few grains. Developed here is a new methodology for calculating TJD strengths and the associated stress fields in large polycrystalline assemblies using experimental electron back-scattered diffraction (EBSD) maps. The methodology combines Bollmann’s approach with a representation of materials as cell complexes. It is computationally efficient and allows for obtaining the spatial distribution of TJD strengths from EBSD images containing thousands of grains. Analysed are the fraction, distribution, and strengths of TJDs within statistically representative microstructures of Cu–0.4%Mg alloy subjected to severe plastic deformation (SPD) by equal channel angular pressing. It is shown that the formation of low-angle grain boundaries (dislocation walls) during SPD leads to an increasing number of TJDs, whose spatial distribution is progressively more uniform and whose strength distribution remains nearly constant. This result suggests that the SPD reduces the internal stresses associated with disclinations in large regions of the material, as closely situated disclinations screen each other’s fields. Regions with high local stresses can be expected between sparsely distributed TJDs with the highest strengths. The average distance between such TJDs could be considered as a natural length scale in a material.

Моделирование взаимосвязи силы резания с глубиной резания и объемами снимаемого металла единичными зернами при плоском шлифовании

Introduction. The model for calculating the cutting force is the basis of the modules of CAM-systems related both to the predicting processing errors on metal-cutting machines for specified grinding conditions, and to the optimizing all parameters of the technological mode (parameters of cutting modes, cutting tools, etc.). However, due to the lack of an adequate model for calculating the cutting force presented in engineering form, such modules have not yet been developed not only for flat grinding operations, but also for all other types of metalworking. It is challenging to obtain an adequate cutting force model for flat grinding operations because it is necessary to establish the interrelation between the machine parameters of the macrocutting modes (feed, cutting speed) of the grinding wheel with the parameters of the microcutting modes — the sets of cutting grains of the wheel associated with the plastic deformation of the metal in the shear zone, microvolumes of the metal being removed and the geometry of the cutting part of the abrasive grains. The purpose of this work is to develop a force model establishing the interrelation of the cutting force with the cutting depth and the volumes of the metal being removed by single grains and the wheel as a whole on the basis of the integration of microvolumes and microforces when metal being removed by the wheel grains. Research methods. The subject of the research is the mathematical modeling of the interrelation between the cutting force and cutting modes with the parameters of microcutting by a group of single grains, based on the equality of work when metal being removed of the same volume. The methodological basis of the research is the connection between the work (energy) spent on the plastic deformation of metal by a single grain, the intensity of stresses, the intensity of deformation rates and the volume of the metal being removed by the wheel as a whole, established by S.N. Korchak. Results and discussion. The result of the study is an analytical model that reliably and adequately establishes the interrelation between the cutting force and the cutting depth, cutting modes, wheel characteristics, physical and mechanical properties of the processing material, and other main technological parameters. The field of application of the results is the possibility of using the cutting force calculation model, presented in this paper, as a basis for the development of a module for a CAM-system (a digital twin of the machining), which would allow to perform the calculation and design of optimal technological parameters of the flat grinding operation, as well as cutting modes testing according to the criterion of processing accuracy of a parts batch, considering the influence of various variable factors and real processing conditions within the manufacturing process.

Surface Roughness Anisotropy and Anisotropic Friction during Plastic Deformation

The isotropy of friction, usually assumed when considering the issues of classical mechanics of bodies and solving engineering problems, is essentially a special case of anisotropic friction, which dominates the nature of friction. This is explained by the objectively existing difference in the properties of the self-organizing medium of the frictional interaction of bodies in different directions. Among these properties are the anisotropy of the physical and mechanical characteristics of the material and its wear, the kinematics of sliding in a friction pair, and the structure of the near-surface layer. An equally important property of the medium generating anisotropic friction is the anisotropy of the roughness of the contacting surfaces. A large number of papers have been devoted to the study of anisotropic friction. They study the friction characteristics of specific materials and friction pairs, the wear resistance of surfaces, models of the dynamics of bodies on a rough surface. Most often these works are experimental in nature. In this article, the influence of roughness anisotropy on anisotropic friction in the processes of plastic deformation of metals is considered at the phenomenological level. A deterministic model of anisotropic (orthotropic) friction is proposed, which makes it possible to determine the magnitude of the friction force and the direction of movement of the deformable metal on the contact surface by the ratio to the vector of the external shear force, depending on the quantitative and qualitative parameters of the roughness of the tool surface. The roughness of the contacting surfaces in the workpiece-tool friction pair is approximated by a set of ordered wedge-shaped protrusions. Contact interaction is considered as the process of deformation of the wedge-shaped protrusions of the workpiece by absolutely rigid wedge-shaped protrusions of the tool. In the process of plastic deformation, an asymptotic approximation of the roughness of the surface of the workpiece to the roughness of the surface of the tool occurs with the full filling of the hollows of the tool irregularities with a plastic wave of the metal of the workpiece.

Effect of mechanical properties of permafrost soil on the stress state of a pipeline during settlements

A brief analysis of methods for calculating the stress-strain state of a pipeline laid in permafrost conditions is given. The analysis of models of interaction of the pipeline with the soil during longitudinal and transverse displacements is given. The tasks of the interaction of the pipeline with the soil are set to determine the place of formation of plastic zones during thawing of the pipeline section. A problem with a symmetrical formulation and a problem in which a semi-infinite pipeline is determined are considered. The places of the highest values of the stress-strain state of a pipeline with a diameter of 1020 mm when two soil massifs moved relative to each other due to soil thawing were determined. The results are shown as a change in the dependence of longitudinal stresses on the amount of displacement. The distribution of stresses in the dangerous section of the pipeline is shown, the most dangerous sections are determined. The process of formation of a zone with plastic deformation of the pipeline wall metal is shown. The main mechanical characteristics of the soil that affect the stress-strain state of the pipeline are determined, an analysis is made of the influence of the mechanical characteristics of the soil on the maximum equivalent stress of the pipeline. Keywords: permafrost; pipeline; soil; mechanical properties; numerical methods; strain; stress.

A study of mechanical characteristics and microstructural evolution of copper-nickel alloy sheet undergoing ultrasonic vibration assisted uniaxial tension

The phenomenon that the ultrasonic vibration (UV) can reduce the flow stress in the metal plastic deformation has been shown in many studies, however, the mechanism of the flow stress decline when the copper-nickel alloy sheet undergoes the UV is unclear yet. In this study, a series of tensile tests are conducted on the copper-nickel alloy sheet. The results indicate that the UV induces softening effect, i.e., the significant decline of the flow stress and the tensile strength. Nevertheless, the elongation of specimens decreases obviously in the tensile tests. To investigate the mechanisms, the microstructure evolution of the copper-nickel alloy sheet in the UV assisted tensile tests are explored by the scanning electron microscope (SEM), the electron backscattering diffraction (EBSD) and the transmission electron microscope (TEM). It is found that after the UV superimposition the high-angle grain boundaries (HAGB) retain more and the reduction of the twinning decreases in the copper-nickel alloy sheet, which impairs the plasticity and the elongation. The results also show that the average grain size under the UV conditions is bigger, which leads to the decrease of the flow stress and weaken the plasticity of the metal.

Characterization and modelling of evolving plasticity behaviour up to fracture for FCC and BCC metals

Yield surfaces evolve depending on loading directions (anisotropic hardening) and stress states (differential hardening) during plastic deformation of sheet metals. A new analytical yield function is proposed by coupling an enhanced pDrucker function and SY2009 anisotropic hardening functions to model both the differential and anisotropic hardening behavior. All the parameters are solved analytically for the proposed function so that the proposed function can model the differential hardening from uniaxial compression to equibiaxial tension and anisotropic hardening of uniaxial tension with three different loading directions. Its convexity during evolution is analysed from plasticity onset to ultimate fracture by a geometry-inspired numerical convex analysis approach. Several tests were conducted for an aluminium alloy 2A12-O and a high-strength steel QP1180 including uniaxial tension/compression, simple shear, notched tension and bulge tests. The proposed yield function is applied to describe the plastic behaviour of AA2A12-O and QP1180 steel under the non-associated flow rule. Parameter calibration is conducted at pre-necking and post-necking stages for modelling yield surface evolution more accurately under large deformation especially at shear and equibiaxial tension states. The applications to the two metals show that the proposed function is more suitable for pressure-sensitive face-centered cubic (FCC) and body-centered cubic (BCC) metals compared to the pressure-coupled Yld2000–2d and CQN models since both the anisotropic and differential hardening behaviours are precisely modelled by the proposed yield function. The proposed function could also be utilized as a stress-based fracture criterion to model four stress states fracture from uniaxial compression to equibiaxial tension.

Properties of Accelerating Edge Dislocations in Arbitrary Slip Systems with Reflection Symmetry.

We discuss the theoretical solution to the differential equations governing accelerating edge dislocations in anisotropic crystals. This is an important prerequisite to understanding high-speed dislocation motion, including an open question about the existence of transonic dislocation speeds, and subsequently high-rate plastic deformation in metals and other crystals.

Lode-dependent anisotropic-asymmetric yield function for isotropic and anisotropic hardening of pressure-insensitive materials. Part I: Quadratic function under non-associated flow rule

It is challenging to precisely model the complicated plastic deformation of metals, including anisotropy in strength and plastic deformation, strength differential effect, anisotropic hardening, etc. A new approach is proposed to extend anisotropic yield functions into asymmetric ones by introducing a Lode dependent function. The approach is applied to the Hill48 function with a Lode-dependent function in a form of the normalized third stress invariant. The proposed Lode-dependent anisotropic-asymmetric (LAA) is applied to characterize the anisotropic hardening behaviors under both tension and compression of QP1180, DP980, AA2008 T4 and α-Ti to verify its performance. The convexity of yield surface evolution with plastic deformation is investigated by a geometry-inspired numerical convex analysis method. The application shows that the proposed LAA function precisely characterizes the anisotropy in tension and compression and its evolution with plastic deformation. It is therefore suggested to model the anisotropic-asymmetric plastic behavior with its applications to metal forming.

Dynamic deformation mechanism in submicro-laminated copper with interlamellar graphene multilayers

The plastic deformation of metals is usually sensitive to loading rates, and such rate-dependent behaviors are influenced by various factors, among which inclusions especially nanoinclusions such as graphene and carbon nanotubes were found to have dramatic influence on the deformation mechanisms of metallic materials. However, relative studies are basically focused in quasi-static regimes. Here, the full spectrum of deformation behaviors of graphene/copper (Gr/Cu) submicro-laminated composites at wide-range strain rates (from 10−4 /s to ≥108 /s) and various temperatures (room temperature and -70 °C) are provided, and relevant mechanisms, especially when deformed at high strain rates and low temperatures, are studied elaborately. Unlike conventional copper materials whose strain rate sensitivity drops dramatically (∼50%) with decreasing temperature, Gr/Cu submicro-laminates has an enhanced strain rate sensitivity that decreases limitedly (∼10%) with temperature. Microstructural analysis revealed that a graphene-assisted deformation mechanism dominated the dynamic compression of Gr/Cu composites, where graphene inclusions act as lubricants that enhanced the deformation ability of the submicro-laminates. Further analysis on copper matrix revealed that dislocation dominated deformation switch to twinning dominated deformation from high to extreme strain rates loading, and extreme loading conditions as well as graphene inclusions are prerequisites for high-density deformation twins in Gr/Cu submicro-laminates.

An experimental–numerical study on the evolution of the Taylor–Quinney coefficient with plastic deformation in metals

When plastic deformation of metals occurs by dislocation motion, a part of the plastic work is stored in the material while the remainder is dissipated as heat. The fraction of the plastic work dissipated as heat can be observed on a macroscopic scale as infrared radiation. Typically, this fraction of plastic work converted into heat is assumed to be constant and around 90%. In this study, an experimental–numerical approach was used to calculate the Taylor–Quinney coefficient as a function of plastic deformation. The experimental foundation was obtained by performing tension tests at slightly elevated strain rates on notched specimens from two dual-phase steels and an aluminium alloy in three temper conditions. The temperature on the surface of the specimens was obtained using an infrared camera, and these temperature recordings were correlated to displacement measurements from a virtual extensometer enabled by digital image correlation. A user material model was used in combination with the thermo-mechanical solver in Abaqus/Standard to perform numerical simulations of the tension tests. Simulations were carried out with both constant and strain-dependent values of the Taylor–Quinney coefficient to examine the effect on the surface temperature in the centre of the specimen during the deformation process. Furthermore, numerical simulations were conducted to find a numerical expression for the Taylor–Quinney coefficient as a function of equivalent plastic strain, such that the temperature evolution in the simulations matches with the temperature measurements from the experiments.

Research of functional symmetry of energy-force parameters of plastic deformation of metals

The equations of energy-power parameters of plastic deformation of metals with functional symmetry are considered, which simplify the calculation. Keywords: plastic deformation, energy-power parameters, functional symmetry, energy consumption, experimental study. brovman@mail.ru