International Journal of Material Forming最新文献

The thermal condition plays an important role in the final thickness distribution and in the mechanical behavior of the Polyethylene Terephthalate (PET) bottle obtained from the stretch blow molding (SBM) process. A complete 3D modelling of the heating stage during the SBM process under industrial condition is very time-consuming. Based on a simplified approach to quickly achieve the numerical simulation of the preform heating, an optimization procedure is proposed to adjust the settings of the infrared lamps by comparing our simulation results to the target temperature profile. In this numerical approach, the radiation source is simulated by using a model for intensity of the incident radiation and the Beer-Lambert law. On the other hand, the ventilation effect under industrial conditions is taken into account by modelling the forced convection around a cylinder. The infrared (IR) flux and ventilation effects are implemented as thermal boundary conditions in COMSOL software for a 3D computation of the thermal problem for the preform only. Since the simulation has a very reasonable computational time, an optimization procedure can be generated to adjust the setting of IR lamps. This optimization tool provides quickly a first set of parameters to help industry to obtain the desired temperature profile.

Blood vessels are essential as they transport oxygen and nutrients. To address the increasing mortality rate from cardiovascular diseases, modern science is focusing on clinical trials for replacing human blood vessels with artificial ones. However, the challenge lies in replicating the intricate anatomy with exact dimensional accuracy on a small scale. This work concentrates on developing innovative fabrication solutions in tissue engineering 3D scaffolds. The study captured two prototypes; one based on traditional manufacturing and the other applied an additive manufacturing principle. Once single-layered construct were manufactured, the results were evaluated in terms of dimensional accuracy measuring the constructs’ length, diameter and thickness. Additional tests were performed for finding the strain at break by applying manual strain-induced method. The samples demonstrated that molding excelled in terms of precision however, the mechanical performance did not meet the ISO 7198 standard. Additive manufacturing approach on the other hand, fully satisfied the structural criteria yet the obtained thickness significantly varied from the given one. Furthermore, efforts were made for fabricating three-layered scaffolds and while AM approach brought preferable results, difficulties were faced with molding. Thus, the importance of this work lies in demonstrating the process capabilities of two methods. The results indicate that while AM is suitable for fabricating multilayered constructs with good structural integrity, molding appears promising for small diameter scaffolds, as it can reduce the anatomical mismatches. Therefore, future work will focus on improving the limitations of these methods for developing three-layered vascular grafts within the admissible dimensional and mechanical criteria.

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.