International Journal of Material Forming最新文献

This study compares the mechanical properties of numerically predicted anisotropic parameters (using the BBC family of models) and experimentally measured results for DC04 steel sheets. The evolution of mechanical properties—such as flow stresses and Lankford coefficient—was analysed during initial plastic anisotropy and mechanical strain hardening in material forming. The results show that the evolution of mechanical properties under isotropic work hardening was predicted with respect to the selected strain levels during tensile testing of the steel. A proposed regression model effectively described the yield stress and r-value behaviour. The Lankford parameter was determined as an instantaneous value based on polynomial fitting of the transverse versus longitudinal true plastic strain curve. Using 08 and 16 independent orthotropic parameters, the BBC criteria family (2003_8p, 2005_8p, 2008_8p, and 2008_16p) was formulated and tested under a non-associated plasticity framework across different material orientations relative to the sheet's rolling direction. Vickers hardness was determined by hardness testing and measuring the two diagonal indentations. The aspect ratio, defined as the ratio of diagonal lengths in the longitudinal direction to those in the thickness direction, was linked to the Lankford coefficient. A strong correlation was observed between experimental hardness measurements and the material's anisotropic properties.

The ridge buckle defect is a perennial challenge in the Steel Industries. Its sporadic appearance at the cold rolling mill (CRM) precipitates the degradation of cold-rolled products. It is unequivocally established that the genesis of this defect lies within the hot strip mill (HSM), manifesting during the cold rolling process subsequent to annealing and skin-pass rolling. In spite of several research attempts, conclusive evidence to definitively resolve this issue remains elusive. This study endeavours to analyse the effect of ramifications of thickness variation in the transfer bar (TB) from the roughing mill, directly fed into the finishing stands of the HSM, on roll wear and strip profile. We hypothesize that this variation may predispose the TB to ridge buckle defects. To investigate this, the study conducts a meticulous statistical and experimental inquiry into the impact of thickness variation in the TB from the roughing mill on the wear of work rolls, which could be a catalyst for ridge buckle defects. The analysis unequivocally corroborates that the incidence of ridge defects is intricately intertwined with the wear profile of the work rolls of last roughing stand (i.e., R5), aligning with the prevailing production conditions within actual plant operations.

Flat punch hole expansion tests are valuable for anisotropic plasticity model evaluation sine they activate a spectrum of tensile stress states across all in-plane material orientations. Pressure-independent yield functions with an associated flow rule typically overlook the state of plane strain tension (PST) during their calibration. Studies have shown that PST occurs near a principal stress ratio of 1:2 for materials that approximately follow deviatoric plasticity but this plane strain constraint (PSC) has been largely overlooked in anisotropic yield function calibration. This study proposes an efficient methodology to characterize and calibrate associated deviatoric plasticity models for materials with a broad range of anisotropy and hardening characteristics including AA5182-O and AA7075-T6 aluminum, and DC04 and 980GEN3 steels. The PST response was evaluated from notch tests using an inverse finite-element analysis approach with correlations provided when cruciform or notch test data is unavailable. The isotropic hardening assumption was evaluated to large strains by determining the stress response from analysis of area of the neck in tensile tests. The anisotropic Yld2000 and Yld2004 yield functions were calibrated to enforce the PSC, ensuring a zero plastic strain increment in directions without a deviatoric stress. The isotropic Hosford and quadratic Hill-48 functions, which universally satisfy and violate the PSC respectively, were also considered. Yield functions that enforced the PSC accurately predicted the global forces, strains, and PST locations in flat punch hole expansion simulations. In contrast, the Hill-48 model failed to accurately predict the radial distance from the hole in PST where the minor strain vanished, highlighting the importance of considering plane strain data for yield function calibration.

This study investigates the high-temperature tensile behavior of AZ31 magnesium alloy under varying current intensities and directions. At 350 °C, with a strain rate of 1 × 10⁻³ s⁻¹ and a peak current density of 50 A/mm², the alloy demonstrates enhanced superplasticity, increasing its true strain at fracture from 0.88 to 1.23. The height-to-diameter ratio of the expanded region improves from 0.45 (without current) to 0.56 under a two-dimensional current field. SEM, EBSD, and TEM analyses reveal that a favourably oriented pulsed current enhances dislocation mobility, facilitates grain boundary sliding and rotation, and promotes recrystallization, contributing to grain refinement.

Magnesium alloys are regarded as the next-generation lightweight structural materials; however, their formability at room temperature remains limited. Hydromechanical deep drawing is an effective technique to enhance the formability of magnesium alloys, with pressure rate (the pressure increment per unit time) being a critical parameter influencing part formability. In this study, a finite element model of an AZ31B magnesium alloy cylindrical component was established to investigate the effect of pressure rate on wall thickness. Under constant process parameters, variations in wall thickness at different pressure rates were simulated, and the impact on minimum wall thickness, thickness distribution, and uniformity was analyzed. Additionally, a predictive equation for wall thickness uniformity of cylindrical parts was developed. Metallographic analysis and hardness testing were conducted to examine the microstructure and hardness distribution in different deformation regions under varying pressure rates, with a focus on explaining the relationship between hardness distribution and microstructure. This study provides insights into the hydromechanical deep drawing mechanism of magnesium alloys from both micro- and macroscopic perspectives, offering a theoretical basis for optimizing the forming process.

Copper terminals with high strength and excellent electrical performance are crucial in power systems of electric vehicles. Radial plastic flow machining (RPFM) is an innovative plastic processing technique that utilizes a specially designed forming channel to fabricate high-performance, gradient-structured (GS) copper terminals in a single step. This study systematically investigated the forming mechanism, mechanical properties, and electrical conductivity of GS copper terminals across varying extrusion thicknesses. The study demonstrated that as extrusion thickness increased, the volume of material flowing into the transverse channel also rose. Consequently, the extent of the low-strain zone across the thickness expanded, whereas the proportion of the high-strain zone remained largely constant. Compared to the original pure copper, the mechanical properties exhibited a combined trend of increased hardness, reduced yield strength, and enhanced ductility. Simultaneously, the electrical conductivity reached up to 99.6% IACS (International Annealed Copper Standard), with virtually no loss in performance. The process established a gradient distribution of grains within the terminals, achieving an optimal balance between high strength, high electrical conductivity, and enhanced ductility, thereby overcoming the traditional trade-off dilemma among these three properties. Therefore, the GS copper terminals fabricated by the RPFM process demonstrated significant performance improvements.

Pressure cure can reduce the cure residual stress (CRS) of solid propellant charges, thereby enhancing the structural integrity and storage life. As the polymerization reaction progresses, it is accompanied by heat release, chemical volume shrinkage, and viscoelastic evolution. In this study, a thermodynamically consistent, fully coupled thermo-chemo-mechanical viscoelastic model is developed. Relaxation tests are carried out on hydroxylated polybutadiene (HTPB) propellant specimens at different cure times revel the viscoelastic evolution mechanism. Consequently, a viscoelastic evolution model is established in relation to the degree of cure (DOC). On the basis, the CRS analysis of the pressure cure HTPB solid propellant charge is performed by means of user material subroutines. The model is validated against literature and experimental results. Furthermore, factors affecting temperature, DOC and CRS are analyzed. Results indicate that the shift factor of HTPB propellant is independent of DOC, while relaxation time first increases and then decreases. Employing the multi-physics coupled viscoelastic model provides a detailed description of the CRS development. An enhanced pressure cure scheme is proposed, which involves releasing partial pressure during cure to future reduce CRS. This model establishes a foundation for designing cure cycles and predicting CRS in solid propellant charges.

Different shot peening sequences can affect the effectiveness of shot peening definitely. To comprehensively investigate the ramifications of different shot peening sequences on the structural integrity of aviation components, this study formulates a shot peening sequence model tailored to the cross-sectional features of H-shaped slide rails commonly found in aircraft, leveraging Abaqus and Python. Combining numerical simulations and experimental data, we utilize the Euclidean distance to assess the similarity of residual stress distribution curves. Effects of six different shot peening surface strengthening sequences on the residual stress distribution and deformation across each surface of the aircraft slide rail’s typical cross-section are analyzed. Results indicate that variability exists in the similarity of maximum residual stress distribution among surfaces subjected to different shot peening sequences. Notably, the fully symmetric strengthening sequence S4 yields the highest similarity in the residual stress distribution curve. Moreover, the maximum deformation of the workpiece groove exhibits a 26.3% disparity under various shot peening strengthening sequences. This indicates that an appropriately selected shot peening sequence can mitigate size errors arising from the strengthening process. This implies that a judiciously chosen shot peening strengthening sequence could enhance the overall shot peening quality of the component.

The increased complexity of geometries and the improved properties of sheet metal components result in narrower process windows, highlighting the need for better process control to minimize deviations and to ensure the production of high-quality parts. In this context, this study focuses on controlling the bending angle of a seat rail component manufactured by a renowned TIER1 company. This angle changes due to material, process fluctuations and post-forming springback. Two types of material, a cold-rolled Dual Phase DP980 steel and a Complex Phase CP980 high-strength steel, are both employed interchangeably when manufacturing this component. Variations in the mechanical properties and thickness of these two materials result in significant differences in post-springback bending angle. To tackle this challenge, various control strategies have been developed including a classical controller and a controller enhanced with a metamodel-based feedforward term. For the latter, two approaches were used: a simulation-based metamodel and an experimental data-based metamodel. Heuristic-based disturbances, reflecting both material variability and process changes (tool mounting variations, tool wear, gap changes and temperature variations), have been considered. To calibrate the new controller parameters and gains, a constrained-based genetic algorithm approach has been utilized together with a numerical virtualization of the process. After this virtual set-up, the new controllers have been tested experimentally in a real environment, using an industrial U-bending tool and a 4000 kN servomechanical press. The new controllers have proven to be an efficient method for enhancing the process robustness. A classical controller, employing a feedback control system, enabled consideration of part-to-part variations. On the other hand, the addition of a metamodel-based feedforward term facilitated anticipation of material properties and sheet thickness changes, thereby preventing scrap production.

To effectively predict the deformation behavior of AZ31B magnesium alloy (Mg alloy) in plastic forming assisted by pulse current, the influences of different pulse currents’ frequencies on the flow stress of Mg alloy were studied. The Voce and Hockett-Sherby constitutive models were modified to include the influence of frequencies, and the parameters of the constitutive models were calibrated based on the experimental data. The Cazacu 2004 yield criterion was improved to describe the yield behavior under the action of pulse current, in which the tensile-compressive asymmetry keeps changing with the increase of plastic strain. The three-point bending tests of AZ31B Mg alloy assisted by different frequency pulse currents were carried out. The improved constitutive model and yield criterion were embedded in ABAQUS using user material subroutine VUMAT for the corresponding three-point bending simulation. It is found that the improved constitutive model and yield criterion considering the current frequencies and tensile-compressive asymmetry can obviously improve the simulation accuracy.

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