Rate Deformation Process Research Articles

Dynamic Mechanical Properties and Modified Johnson-Cook Model Considering Recrystallization Softening for Nickel-Based Powder Metallurgy Superalloys.

The material undergoes high temperature and high strain rate deformation process during the cutting process, which may induce the dynamic recrystallization behavior and result in the evolution of dynamic mechanical properties of the material to be machined. In this paper, the modified Johnson-Cook (J-C) model for nickel-based powder metallurgy superalloy considering dynamic recrystallization behavior in high strain rate and temperature is proposed. The dynamic mechanical properties of the material under different strain rates and temperature conditions are obtained by quasi-static compression test and split Hopkinson pressure bar (SHPB) test. The coefficients of the modified J-C model are obtained by the linear regression method. The modified model is verified by comparison with experimental and model prediction results. The results show that the modified J-C model proposed in this paper can accurately describe the mechanical properties of nickel-based powder metallurgy superalloys at high temperatures and high strain rates. This provides help for studying the cutting mechanism and finite element simulation of nickel-based powder metallurgy superalloy.

A Review of Numerical Simulation and Modeling in High Strain Rate Deformation Processes

Numerical simulation and modeling play a crucial role in understanding and predicting the behavior of materials subjected to high strain rate deformation processes. These processes involve rapid deformation and loading rates, typically encountered in scenarios such as impact events, explosive detonations, metal forming, and crash simulations. By employing advanced computational techniques, researchers and engineers can gain insights into complex material behavior under extreme loading conditions. This paper provides an overview of numerical simulation and modeling approaches used in studying high-strain rate deformation processes. It discusses the challenges associated with capturing dynamic material response, the development of constitutive models, and the use of finite element analysis and computational fluid dynamics. The paper also highlights the importance of material characterization, model validation, and sensitivity analysis for accurate and reliable simulations. Additionally, it explores the application of numerical simulations in optimizing material properties, designing protective structures, and improving the performance of impact-resistant materials. Overall, this review paper emphasizes the significance of numerical simulation and modeling as powerful tools for advancing the understanding and design of high-strain rate deformation processes.

Understanding the role of monolayer graphene during long range shock strengthening of metal-graphene heterostructure

Graphene has been extensively used in graphene reinforced metal composite, with strengthening effects due to its ability to block dislocation from propagation during the traditional low strain rate deformation process. Laser shock peening has been applied in graphene/metal composites with graphene concentration of 2–10% with a relatively close distance between the graphene layers. This work discovered a strong long-range coupling effects of graphene as a super-strong nanomaterial and shock-wave transmitter during laser shock processing under room temperature LSP and cryogenic temperature (cLSP), under extremely low graphene concentration (1.42 × 10−6% vol.). Compared with simple compressed graphene-copper heterostructure, the yield strength of LSP and cLSP processed samples increases by 40%, and 76% respectively. We found that under laser shock peening (LSP) process, the shock wave can pass through long-distance to generate dislocation transportation from one layer to another graphene with the shock wave interaction between graphene layers separated very far away. Graphene plays an important role not only as a transmitter of shock waves, but also as a strong wall to bounce back shock waves to generate high dislocation density around graphene layers. We have designed experiments to compare the deformation behavior of the laminates under three deformation conditions: compression, LSP, and cLSP, respectively. It was found that the compressed sample has very few parallel dislocation arrays beneath the graphene interface, indicating that graphene blocks the dislocation movement and has very limited strengthening effects. The LSP processed samples contain much high dislocation density, while even higher density dislocation and strength are found in cLSP due to faster shock transportation in graphene/metal layers under cryogenic conditions. Finite element modeling was used to investigate the shock wave interaction with the graphene and metal layer under various conditions, which is consistent with experiments. Molecular dynamics simulation is used to simulate the microstructure of the laminates under various conditions and validated by experiments. This work provides a starting point to understand the long-range strengthening effects of 2D nanomaterials of extremely low concentrations and provide new design strategies for manufacturing graphene-metal nanocomposite and their strengthening approaches.

Effect of strain rate on formability of 22MnB5 steel during hot stamping process

Hot stamping is a high temperature and high strain rate deformation process, which is widely used in automotive industries because of the advantages associated with the process like higher formability, no spring back, higher specific strength to weight ratio etc. When strain rate increases, the formability of materials decreases but in some conditions reversal behavior was also observed, therefore in this work, the focus is to find the effect of strain rate on thickness distribution, thickness gradient evolution and formability of 22MnB5 Steel. To capture the effect of strain rate, a wide range of high-temperature tensile tests were conducted in the thermomechanical simulator (Gleeble-3800) for different strain rates (0.01, 0.1, 1/s) under uniaxial and plain strain conditions. It is found that formability of 22MnB5 steel increases with increase in strain rate in the drawing region.

Dynamic Impact Response of Ultrafine Grained AA5052 Aluminum Alloy Processed Via Multiaxial Forging at Cryogenic Temperature

In this study, high strain rate mechanical test was conducted on ultrafine-grained AA5052 aluminum alloy using the Split-Hopkinson Pressure Bar experiment. The AA5052 aluminum alloy was processed via multiaxial forging under cryogenic condition at two different cycles to achieve grain refinement and ultimately, increase in strength of the material. The average strain rates that the specimens were subjected to during the Split-Hopkinson Pressure Bar experiment ranges from 1000 s-1 to 5000 s-1 at an increment of 1000 s-1. The EBSD map shows that the average grain size of the AA5052 aluminum alloys for the samples processed at 4-cycles is approximately ~900 nm while the samples processed at 6-cycles have a lower average grain size of approximately ~700 nm due to being subjected to more plastic deformation during the processing. The high strain rate deformation process of both specimens was dominated by thermal softening with minima strain hardening effect. During the deformation, the maximum flow stress experienced by samples that was processed at 4-cycles is 410 MPa at 5000 s-1 strain rate while samples processed at 6-cycles has 494 MPa at 3000 s-1. Strain hardenability is not dominant in the deformation mechanism but relative to AA5052 CF (4-cycles), AA5052 CF (6-cycles) has a better strain hardening exponent as the strain rate increases. Both specimens have the highest strain hardening exponent at 1000 s-1 which is 0.1544 and 0.134 for AA5052 CF (4-cycles) and AA5052 CF (6-cycles), respectively. Our results show that AA5052 CF (6-cycles) possesses better mechanical properties under high strain rate in comparison with AA5052 CF (6-cycles).

Formability and mechanism of pulsed current pretreatment–assisted laser impact microforming

Pulsed current treatment was introduced into the laser impact microforming technology to improve the formability of laser impact forming. A pulsed current pretreatment–assisted laser impact microforming technology is proposed, and the formability and mechanism of such composite technology are discussed. In this study, the mechanical properties of H62 brass before and after pulse treatment were tested. The effect of pulsed current treatment on the formability of the material under high strain rate was studied by a laser impact free microbulging experiment. Moreover, the mechanism of pulsed current influence on the material’s formability was analyzed from the aspects of microstructure, texture evolution process, and grain size and morphology. Results showed that the elongation of the material was increased obviously, the flow stress during the tensile process was decreased significantly after pulsed current treatment, and the fracture form of the material gradually evolved from brittle fracture to ductile fracture. The forming height of samples under high strain rate improved greatly which may be due to the high-density pulsed current treatment that significantly alleviated the dislocation entanglement in the material. Owing to the weaker orange-peel effect which is induced by smaller recrystallized grains and lower maximum density of texture, the surface quality of formed parts after pulsed current treatment increased remarkably. In addition, the more uniform section thickness distribution of formed parts was observed, which may stem from obviously refined grains after pulsed current treatment improved the fluidity of the grains in a high–strain rate deformation process.

Electromagnetic Formability of an Aluminium Ice Tray

Electromagnetic forming (EMF) is a typical high speed forming process using the energy density of a pulsed magnetic field to form work sheets made of metals with high electrical conductivity like aluminium alloys, which have low formability at low strain rate. Under high velocity forming, metallic materials exhibit an increase of flow stress and ductility with increasing deformation rate. Therefore, materials of lower ductility can be deformed to higher strains using high strain rate deformation processes such as electromagnetic or explosive forming techniques. In this paper analysis of an electromagnetic sheet metal forming process is carried out by using commercial finite element software LS-DYNA®, which incorporates a sequential coupling method involving electromagnetic field, structural and thermal solutions. Study of process parameters for forming aluminium ice tray (used in refrigerator) by Electromagnetic forming process has been carried out, simulation was done involving a die, Al worksheet and a spiral coil.

Ultrahigh dense and gradient nano-precipitates generated by warm laser shock peening for combination of high strength and ductility

Nanocrystalline materials generated by severe plastic deformation often come with high strength but low ductility due to the inability to accumulate dislocations and thus the low work hardening rate. In this study, a unique high strain rate deformation process – warm laser shock peening (WLSP) – is studied to generate extremely high-density nano-precipitates in precipitation hardenable alloy. Aluminum alloy (AA) 7075 was selected to evaluate the generation of ultra-high-density precipitates by WLSP and the effects on the strength and ductility. WLSP integrates the advantages of laser shock peening (LSP), dynamic strain aging (DSA) and dynamic precipitation (DP). The nanoscale precipitate particles generated by WLSP effectively block dislocations and thus increase the material strength. The precipitate–dislocation interaction has been observed by high resolution TEM (HR-TEM) and modeled by the multiscale discrete dislocation dynamic (MDDD) model. It has been demonstrated that compared with room temperature LSP, WLSP can improve material strength by 32.3% without compromising the ductility, in that elongation remains 20%. These ultra-high-density nano-precipitates greatly improve dislocation accumulation capacity and thus effectively increase ductility.

Simulation of damage evolution in ductile metals undergoing dynamic loading conditions

A set of constitutive equations for large rate-dependent elastic–plastic-damage materials at elevated temperatures is presented to be able to analyze adiabatic high strain rate deformation processes for a wide range of stress triaxialities. The model is based on the concepts of continuum damage mechanics. Since the material macroscopic thermo-mechanical response under large strain and high strain rate deformation loading is governed by different physical mechanisms, a multi-dissipative approach is proposed. It incorporates thermo-mechanical coupling effects as well as internal dissipative mechanisms through rate-dependent constitutive relations with a set of internal variables. In addition, the effect of stress triaxiality on the onset and evolution of plastic flow, damage and failure is discussed. Furthermore, the algorithm for numerical integration of the coupled constitutive rate equations is presented. It relies on operator split methodology resulting in an inelastic predictor–elastic corrector technique. The explicit finite element program LS-DYNA augmented by an user-defined material subroutine is used to approximate boundary-value problems under dynamic loading conditions. Numerical simulations of dynamic experiments with different specimens are performed and good correlation of numerical results and published experimental data is achieved. Based on numerical studies modified specimens geometries are proposed to be able to detect complex damage and failure mechanisms in Hopkinson-Bar experiments.

Dynamic recrystallization of tungsten in a shaped charge liner

Dynamic recrystallization (DRX) of tungsten was investigated through the microstructural examination of a recovered shaped charge slug, using both optical and transmission electron microscopy. The microstructure was refined, indicating the DRX process occurred during deformation. No twins or elongated subgrains were observed due to the extremely high strain rate deformation process. This proves that the DRX process was dominated by dislocation movements. Compared with previous reports of copper and tantalum shaped charges, the tungsten liner deforms more like copper than tantalum.

Influence of Deformation Variables on Cavitation of a Superplastic 5083 Aluminum Alloy

A series of experiments were performed under various strain rates and strain states during superplastic deformation of a fine-grained 5083 aluminum alloy. Uniaxial tensile tests, rectangular pans, hemispherical and cylindrical capped parts were superplastically deformed to study the effects of forming rates and strain states on the nucleation and growth characteristics of cavities. The results showed that cavity fraction increased with increasing temperature due to greater grain growth. Strain states did have an effect on the cavity fraction in formed parts. A two-step strain rate deformation process could reduce cavitation.

Impact deformation of polymeric projectiles

Post-impact deformation of projectiles is studied in relation to flyer-plate thickness and standoff distance from a rigid anvil, without significant penetration and perforation of the flyer plate. A close-range photogrammetric measuring technique is used to determine the final profiles of polymeric cylindrical projectiles. This non-destructive measurement technique is utilized to study the effects of projectile nose geometry on the high rate deformation process, at speeds ranging from 100 to 600 m/s, in connection with metal sheet deformation during impact spot welding. An Imacon ultra-high speed camera is used to photograph the deforming polymeric projectiles.

An estimate of internal stress evolution in the primary creep based on the composite model of dislocation structure

Abstract The paper gives an estimate of the average internal stress which can be measured by the strain transient dip test technique in the heterogeneous dislocation structure consisting of cells or subgrains bounded by low-angle subboundaries. The structure is described by the two-component model of hard and soft regions and the process of creep is considered an iso-strain rate deformation process. An evolution of the internal stress is derived from the evolution of dislocation structure characteristics in the normal primary creep and is evaluated for alpha iron from experimental data which were published earlier by the present author ( Philos. Mag., 25 (1972) 865; 28 (1973) 891, 1099). As an illustration of local conditions, local stresses and local strain rates are evaluated. The results document a growth of the mean internal stress in creep and changes of local stresses in the hard and the soft region. The internal stress values are relatively low and do not approach the value found experimentally in the steady-state creep which reaches the value of long-range internal stress in the soft region. A suggested interpretation of this discrepancy is based on an assumption that the actual steady-state creep has not yet been reached in the region of constant creep rate.

Application of the FEM to elastoplastic wave propagation in metals

Under dynamic loading shock waves propagate in metallic materials and may be concentrated after reflection from fixed boundaries. In these cases high strain rate gradients are initiated in the material, which are accompanied by a change in temperature due to the adiabatic character of high rate deformation processes. In order to estimate the mechanical behaviour of the material under multiaxial dynamic loading constitutive equations must be worked out, which have to be valid over wide ranges of strain rate and temperature. Often a viscoplastic behaviour is assumed using the equation of Perzyna: