International Journal of Material Forming最新文献

Magnesium alloys are known for their poor plasticity at room temperature, making them difficult to form. Typically, heating is required to enhance their formability. However, even heat-assisted forming has limitations when it comes to improving the quality of the formed components. To further enhance the forming quality of magnesium alloys, this study explores the use of vibration in conjunction with heating, specifically through a multi-pass incremental forming process for magnesium alloys under combined thermo-vibratory effects. The research integrates thermal-vibration parameters with forming process parameters for comprehensive analysis. Initially, orthogonal experiments were conducted to examine the influence of different thermal-vibration parameters, such as temperature, vibration frequency, and amplitude, on the wall thickness and geometric accuracy of the workpiece. This analysis led to the determination of an optimal combination of thermal-vibration parameters. Subsequently, under these optimal thermal-vibration conditions, the effects of single-process parameter variations, including inter-pass angle, tool diameter, and layer spacing were examined, and their interactions on forming quality. Experimental validation confirmed the accuracy of the simulation model used in this research. The results revealed that the optimal thermal-vibration parameter combination consists of a forming temperature of 250 °C, a vibration frequency of 30 kHz, and an amplitude of 0.01 mm. Under these conditions, the minimum wall thickness of the workpiece improved by 3.24%. Furthermore, among the process parameters, the inter-pass angle had the most significant impact on forming quality, followed by the tool diameter, while layer spacing showed the least influence.

This study investigates the influence of natural aging on the formability and plastic deformation behavior of AA 2198, a third-generation Al-Li alloy, under W-temper conditions to address its low formability. Mechanical tests, including uniaxial tensile, bulge, and Nakazima tests, were performed to evaluate the evolution of mechanical properties, anisotropy, and formability during natural aging. A phenomenological hardening model was developed and validated through yield surfaces and finite element simulations, incorporating insights from forming limit tests. During natural aging, yield strength and ultimate tensile strength increased, while elongation decreased. Natural aging was completed within 7.6 days, with solute and precipitation strengthening identified as primary mechanisms. Anisotropy appeared during early natural aging but remained stable, attributed to the aluminum crystal structure and rolling-induced crystallographic texture, independent of natural aging effects. The proposed hardening model effectively predicted the evolution of yield strength, anisotropy, and formability across natural aging conditions. The forming limit curve for natural aging at 0.5 h was significantly higher than other conditions, demonstrating enhanced formability through W-temper heat treatment. Finite element simulations and forming tests revealed that natural aging at 0.5 and 6.0 h supported stable forming, with natural aging at 6.0 h offering optimal thickness distribution and safety margins. Beyond 24.0 h of natural aging, formability diminished significantly due to wrinkling and fractures. This study highlights the utility of the hardening model and numerical framework as efficient virtual tools for optimizing the W-temper forming of aerospace components.

Hydroforming is an advanced technology that enables integrated forming for complex components and promotes lightweight construction and high reliability. However, the hydroforming process can result in a strain gradient at the wall thickness of tubes, which directly determines the deformation order in the thickness and is closely linked to the occurrence of defects like springback and wrinkling of tubular components. In this study, a geometric model of tube hydro-bulging that considers wall thickness was established, and the effects of length-diameter and diameter-thickness ratios on the radial strain gradient were studied through theoretical analysis and numerical simulations. Higher strains are experienced on the inside and lower on the outside during tube bulging. The strain disparity increases with greater length-diameter ratios and decreasing diameter-thickness ratios. In the case of a tube with an outer diameter of 78 mm and a wall thickness of 4 mm, the maximum equivalent strain difference observed was 0.03. Additionally, a tube hydro-bulging test was carried out to confirm the microstructural gradient, with high-density dislocations concentrated near the inner surface, resulting in noticeable strain localization. This study reveals the radial deformation mechanism of hydroformed tubular components, essentially providing a reliable scientific basis for controlling defects in tubular parts.

In this study, a finite element simulation strategy was developed to analyze the green tire building process, with the goal of identifying existing defects and guiding the refinement of process parameters. The mechanical behaviors of uncured rubber in various tire components were investigated through cyclic loading and unloading experiments conducted at two different strain rates. A viscoelastic constitutive model was adopted to describe the nonlinear elasticity and hysteresis effects of uncured rubber under large deformation. Then the finite element models including a two-dimensional (2D) axisymmetric model for lamination step and a three-dimensional (3D) model for the remaining building steps were constructed to simulate the whole process. The green tire cross-section profile obtained from simulation is in good agreement with the actual one obtained through 3D scanning, thereby verifying the reliability of the simulation. Additionally, the deflection angle of cords was simulated and verified through green tire cutting experiments. Finally, factors affecting cord deflection were identified, including an intrinsic factor (radial displacement) and an extrinsic factor (deflection angles of nearby cords). Two improvement measures, reducing the radial displacement of cords and the influence from nearby cords, were proposed to reduce the misalignment of the carcass cords, and the effectiveness of measures was validated by simulation.

Friction stir welding (FSW) is a renowned joining technology for creating difficult-to-be-welded or non-weldable dissimilar material joints engendering viscoplastic flow at the interface. The present work compares the evolution of the material flow and properties during FSW of extremely different materials, viz., Aluminum alloy 6156 and commercially pure Ti Grade 2 with the help of numerical simulation and practical. The necessity of the appropriate heat flux to be achieved through balancing parameters was realized through simulation and experimental outcomes. In this paper, a specialized numerical model specifically designed to account for the presence of two distinct alloys, was employed to examine the effects of process parameters on temperature distribution, strain distribution, and material flow through velocity vectors. Valuable insights relating to material flow patterns observed while altering the mutual skin stringer positions have been elaborated. Macrostructural and microstructural characterizations were carried out to understand the localized material microstructural evolution comprising grain refinement, intermetallic, defects, etc. The parametric influence on grain morphologies, intermittent phases, joint strengths, and hardness are discussed in depth. Interestingly, the joint strength values recorded for prepared T-joints are comparable with the ones found for butt joint configurations reported in the literature.

Thin-walled 304 stainless steel tubes with annular inner ribs have high strength, high stiffness, and light-weighting characteristics, and have wide applications in the aviation, aerospace, and navigation fields. In this study, stainless steel thin-walled tubes with inner ribs were manufactured by hot power backward-spinning. The microstructural morphology, microhardness, and main texture evolution of typical regions of the tube were characterized and tested. The influence of different stress-loading conditions on the microstructure and mechanical properties of the tube was mainly studied. The numerical simulation for the hot spinning forming process of 304 stainless steel was carried out to analyze the material flow rules in the regions of inner rib and wall-thinning, as well as predict the height of inner ribs with different spinning parameters. The results showed that the thinning of the wall of the tube region is obvious, and the material in the inner rib region fills into the groove of the mandrel, and the loading paths of stress on the materials in these regions are different, and the wall-thinning region is subjected to axial and radial loads accuring plane strain, which leads to the transformation from the original equiaxial crystalline to elongated grains. The microstructure of the sample presented strong < 111>//AD texture for the reason of acutely axial load born from rotating tools during spinning. This study provides a reliable theoretical basis and technical reference for the optimization of the spinning forming process of stainless steel thin-walled tubes with annular inner ribs.

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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.