International Journal of Material Forming最新文献

With special reference to the modelling of hot roll bonding, new experimental procedures to measure the resulting bond strength for a combination of AA6016 and AA8079 aluminum alloys at elevated temperatures and various strain rates using laboratory tests are proposed. The data acquired by this procedure is used to developed and calibrate a semi-empirical model, which accurately predicts the resulting bond strength within an error of 2 MPa on average. It is shown that the bond strength generally follows the flow stress regarding the dependency on temperature and strain. Additionally, inter-pass times can increase the bond strength, provided that both a suitable temperature and timespan are realized. Contrary, multiple consecutive height reductions were found to reduce the bond strength.

In this paper, a prediction model for the pressure-axial feed loading path in the hydroforming process of a bi-layered Y-shaped tube is developed. The plastic deformation behavior of the bi-layered Y-shaped tube in the hydroforming process is investigated by categorizing the entire process into four stages: yielding, preforming, plastic forming, and shaping. By conducting stress–strain analysis on the central unit of the bi-layered Y-shaped tube branch area and incorporating the Von-Mises yield criterion, the Levy–Mises flow rule and the principle of volume invariance, rational ranges for internal pressure and axial feed at various stages of the bi-layered Y-shaped tube hydroforming process are identified. Therefore, a predictive model for the loading path of the bi-layered Y-shaped tube hydroforming process, controlled by internal pressure and axial feed under various strain conditions, is developed. The effectiveness of the prediction model was validated through finite element simulations and experimental methods. This predictive model can be used to guide the setup of loading paths for bi-layered Y-shaped tubes and other similar inclined tee tubes.

This study proposes to study the sliding and slippage mesoscopic defects that appear during the preforming phase of dry reinforcements to produce complex composite shapes. For this purpose, experimental preforming tests were conducted on a plain weave fabric with low cohesion using a specific punch developed specifically for this purpose, and which combines the geometric facets of a square and a tetrahedron. The tests were conducted under several configurations varying the blank holder pressure intensity as well as its distribution, through the number and springs position that generate normal forces on the blank holders. The results showed that the corners of the geometry formed by orthogonal faces favor the appearance of mesoscopic defects and specifically slippage because of its severity. Sliding has shown itself to be very sensitive both to the singularities of the geometry where it appears, and to the heterogeneity of the pressure distribution of the blank holders. On the other hand, the sliding, which appears in the vicinity of the slippage on flat faces, is rather sensitive to the distribution of the pressure. The increase in the blank holder pressure, regardless of the conditions of its application, leads to an almost linear increase in the extent and number of these mesoscopic defects.

The microstructure evolution, plastic deformation, and damage severity during the open die hot forging of a martensitic stainless steel were investigated using finite element (FE) simulation. A microstructure evolution model was developed and combined with a visco-elastoplastic model to predict the strain, the strain rate, and the temperature distribution, as well as the volume fraction and the size of dynamically recrystallized grains over the entire volume of an industrial size forging. The propensity to damage during hot forging was also evaluated using the Cockcroft & Latham model. The three models were implemented in the FE code and the results analyzed in terms of microstructure inhomogeneity and stress levels in different regions of the forging. A good agreement was obtained between the predicted and the experimental results, demonstrating that the simulation provided a realistic representation of the forging process at the industrial scale.

This paper focuses on calibrating and modeling of distortional hardening behaviours in twinning induced plasticity steels. True stress-strain curves for uniaxial tension, plane strain tension, and pure shear specimens are inversely identified from corresponding load-displacement curves. The study reveals that accurately predicting the hardening behaviours of TWIP980 steel under plane strain tension and pure shear stress states is challenging with an isotropic hardening model, and a negative hydrostatic effect for TWIP980 is observed through shear testing. A novel distortional hardening model is proposed to simultaneously accommodate the three stress states on the contours of plastic work. Coefficients of the distortional hardening model are calibrated at discrete levels of plastic work and then interpolated to describe the distortion of the initial yield surface. The model is then expanded to consider the true stress-strain curves under uniaxial tension along 0, 45 and 90-degree directions, as well as under the plane strain tension along the 0-degree direction simultaneously. This expansion explicitly incorporates the three true stress-strain curves under uniaxial tension, with the curve of plane strain tension captured by an evolutionary exponent related to plastic work. The developed distortional hardening models demonstrate reasonable reproduction of load-displacement curves for TWIP980 steel under uniaxial tension, plane strain tension, and pure shear stress states.

The finite element method combined with the experiment analyzed the evolution mechanism of the plastic strain state and warping deformation of the TA2/Q345R composite plate during heat treatment. Then, the factors influencing plastic strain state and shape warping in the composite plate were discussed. The results show that during the heat treatment process, the composite plate’s internal strain state and macroscopic shape state are impacted by the thermal strain and bending strain between the heterogeneous metal layers, and both are in a continuous dynamic variation state. Therefore, the ultimate deformation behaviour of the composite plate depends on the accumulation and inheritance of plastic deformation during heat treatment. There is a critical value of the composite ratio and the total thickness of the composite plate, respectively, which determines the direction of the warpage after heat treatment.

In this study, a new process of axial ultrasonic vibration-assisted extrusion cutting (AUV-EC) is proposed to prepare Al6061 alloy ultrafine-grained chip strips. The principles of AUV-EC are analyzed. The cutting motion trajectory equations of the main tool and the constraint tool during the AUV-EC process are established, and the theoretical cut marks on the chip surface are predicted. AUV-EC experiments are conducted to verify the theoretical cut marks on the chip surface and characterize the surface topography and microstructure of the chip strip samples. The results show that applying ultrasonic vibration with a frequency of 33 ~ 34.5 kHz and an amplitude of 1 ~ 6 μm in the AUV-EC process can improve the chip strip’s surface quality. Compared with traditional extrusion cutting (EC) chip samples, AUV-EC chip samples have better surface flatness and smoothness and lower surface defect ratios. The average grain sizes of the traditional EC and AUV-EC chip samples are approximately 164 nm and 135 nm, respectively. Many dynamic recovery grains are distributed in traditional EC chips, but there is only a small amount in AUV-EC chips. The x-ray diffraction (XRD) test finds that the AUV-EC chip has a higher dislocation density.

This study aims to provide precise predictions for the compression of reinforced polymers during the sheet Molding Compound (SMC) process, ensuring the attainment of a predefined structure while preventing material overflow during the process. The primary challenge revolves around identifying the optimal initial shape to prevent material rebound during the process. To confront this issue, a numerical model is utilized, faithfully simulating the SMC process and forming the foundation for our investigations. Furthermore, to optimize the pre-fill stage, a surrogate model is proposed to enhance modeling efficiency, and then an inverse analysis method is applied. This approach of minimizing material rebound during the SMC process results in a reliable metamodel to predict an initial mass shape accurately and at a low computational cost, thus ensuring the squeezed material fits the mold shape.

This article deals with the thermoforming process, in which the plastic sheet is heated to a suitable temperature and stretched through a single-sided mould. This paper focuses on the study of thickness distribution along the final part through numerical simulation with T-SIM software and optical characterization of the practical process. PC LEXAN™ 8A13E films, with different initial thickness, were moulded by two types of moulding (positive and negative). It was intended to evaluate, characterize and correlate the effect of the process on the optical properties of the films. The findings of the study suggest that films formed with a negative mould exhibit more pronounced thickness variations compared to those formed with a positive mould, resulting in lower final thicknesses. Additionally, thicker films exhibit higher thickness variations after thermoforming, as supported by the experimental data. Regarding the optical characterization of the films, transmittance and reflectance tests were performed. In the case of transmittance, a significant increase in this property is observed after thermoforming, while a decrease in the reflectance values was observed. This paper is then focused on the study through numerical simulation and optical characterization of the thermoformed films, elucidating the dynamics inherent in the thermoforming process with transparent polycarbonate films, providing valuable insights for optimization and application across various industrial sectors.

Deep-drawing is a method in which flat sheets of metal are formed into complex 3-dimensional geometries. Three main types of challenges arise when transitioning from the macro-scale to micro-deep drawing. These can be summarised as: (1) tribological effects, which mainly stem from the relative difference in surface characteristics between the two size scales, (2) material behaviour effects which arise from the increasing heterogeneity of materials that have a decreasing number of grains that are deformed in forming, and (3) dimensional effects which relate to difficulties in handling and inspection of small components at high rates and challenges in manufacturing and monitoring of tool components for use in micro-deep drawing. Various methods or effects can be applied to micro-deep drawing processes to tackle these challenges. This paper reviews research on methods and effects that can be used to improve the robustness in micro-deep drawing processes. Small changes, such as the choice of lubricant and slight changes to the punch geometry are considered, but so are larger changes such as the use of ultrasonic vibration to improve formability and adjustable tooling. The influence of process monitoring and simulation on process robustness is also considered. A summary of methods and effects is drawn at the end to highlight potential space for innovation.