International Journal of Material Forming最新文献

New structural sheet metal parts are developed in an iterative, time-consuming manner. To improve the reproducibility and speed up the iterative drawability assessment, we propose a novel low-dimensional multi-fidelity inspired machine learning architecture. The approach utilizes the results of low-fidelity and high-fidelity finite element deep drawing simulation schemes. It hereby relies not only on parameters, but also on additional features to improve the generalization ability and applicability of the drawability assessment compared to classical approaches. Using the machine learning approach on a generated data set for a wide range of different cross-die drawing configurations, a classifier is trained to distinguish between drawable and non-drawable setups. Furthermore, two regression models, one for drawable and one for non-drawable designs are developed that rank designs by drawability. At instantaneous evaluation time, classification scores of high accuracy as well as regression scores of high quality for both regressors are achieved. The presented models can substitute low-fidelity finite element models due to their low evaluation times while at the same time, their predictive quality is close to high-fidelity models. This approach may enable fast and efficient assessments of designs in early development phases at the accuracy of a later design phase in the future.

4D printed hydrogels are 3D printed objects whose properties and functions are programmable. In the definition of 4D printing, the fourth dimension arises from the ability of printed structures to change their shape and/or function over time when exposed to given conditions environmental stimuli, during their post-press life. Stimulation-responsive hydrogels produced by the emerging 4D bioprinting technology are currently considered as encouraging tools for various biomedical applications due to their exciting properties such as stretchability, biocompatibility, ultra-flexibility, and printability. Using 3D printing technology, customized functional structures with controllable geometry and trigger ability can be autonomously printed onto desired biological interfaces without considering microfabrication techniques. In this review, by studying the progress in the field of hydrogels for biointerfaces, we summarized the techniques of 4D printing gels, the classification of bioinks, the design strategies of actuators. In addition, we also introduced the applications of 4D hydrogels in tissue repair, vascular grafts, drug delivery, and wearable sensors. Comprehensive insights into the constraints, critical requirements for 4D bioprinting including the biocompatibility of materials, precise designs for meticulous transformations, and individual variability in biological interfaces.

The present work investigates the effect of rotational speed on joint quality during Friction Stir Spot Welding (FSSW) using a consumable pin, where a consumable pin is used with a rigid tool shoulder for welding AA6061-T6 sheets to produce an exit-hole-free FSSW joint. Joint quality was analysed using lap shear test, macrostructure, microstructure and microhardness analysis at five rotational speeds, viz. 360, 462, 557, 900 and 1200 revolutions per minute (RPM). The joint strength increased with increase in rotational speed from 360 RPM to 900 RPM and then decreased with further increase in rotational speed. A 1.7 times increase in joint strength was observed for FSSW at 900 RPM with reference to 360 RPM. As expected, both energy input and temperature increased with rotational speed. The energy input increased by only 27.5% as the rotational speed was increased from 360 to 900 RPM. Finite element (FE) simulations were conducted for validation and study using commercial FE software, DEFORM-3D, to predict temperature distribution, force, torque and material flow. Lap shear test simulations matched with experimental results within reasonable (∼7%) accuracy except for very low rotation cases. However, failure load provided better matching with experimental results when Cockcroft-Latham damage model was used instead of Freudenthal damage model.

This paper presents results acquired from experimental investigations into determining the influence of cyclic-bending-under-tension (CBT) and annealing on elongation-to-fracture (ETF) and tradeoffs in strength and ductility of three Mg sheet alloys: ZEK100, BioMg250, and Mg4Li. The CBT process imparts uniform deformation greater than achievable in simple tension (ST) incrementally by subjecting a sheet specimen to simultaneous tension with a crosshead motion and bending with a set of rollers reciprocating along the specimen. The space of process parameters including crosshead velocity and bending depth is explored initially to achieve the greatest ETF of ZEK100 alloy. Improvements in ETF of about 40% are attained using CBT relative to ST. Given the uniform deformation imparted by CBT to large plastic strains, tradeoffs in strength and ductility of the alloy are investigated next by subjecting the alloy sheets to a certain number of CBT cycles under the optimized parameters and subsequent annealing. Strength of the alloy is found to increase by a factor of 1.4 along the sheet strongest direction, the rolling direction, and a factor of 2 along the sheet softest direction, the transverse direction. Since the strength improved more along the soft direction than along the hard direction, the alloy anisotropy reduces. Significantly, the strength can increase for about 40% along the soft direction, while reducing the anisotropy and preserving at least 10% of the alloy ductility in every direction. Characterization of microstructural evolution using electron-backscattered diffraction and texture evolution using neutron diffraction revealed slip dominated deformation of the alloy. Similar processing and testing of BioMg250 and Mg4Li sheet alloys produced even better results in terms of enhancing elongation and improving the contrasting strength and ductility properties. Comprehensive data for the three alloys and insights from the investigations are presented and discussed.

In this study, microstructure, recrystallization texture, and mechanical properties of Al/WO₃/SiC hybrid nanocomposite was investigated by electron backscatter diffraction (EBSD), analysis of orientation distribution function (ODF), and uniaxial tensile test during accumulative roll bonding (ARB) process. Microstructural observations show that the recrystallized grains are elongated in the rolling direction (RD) due to the Zener-pinning of nanoparticles at high angle grain boundaries and therefore growth is inhibited in the normal direction (ND) during the ARB process. The ODF investigation confirmed that after 5 cycles of ARB process, recrystallization is associated with nucleation of Goss, Q, and P components. When the number of ARB cycle was increased, Goss and Q recrystallization textures were eliminated, but on the other hand, the P, B and B* texture components were strongly developed. The ND-Cube and RT-Goss recrystallization texture is also formed with low intensity at the last stages. Also, the A and A^* shear textures which formed in the fifth cycle, shifted towards the Dillamor and Cu textures with increasing the number of ARB cycles. Furthermore, the samples were heated using DSC under Argon atmosphere with four different heating rates. The Kissinger, Ozawa, Boswell, and Starink methods were used to determine the recrystallization kinetics. It can be seen that recrystallization temperature and thereby activation energy (E_a) decreases with increasing the number of ARB cycles. Furthermore, the tensile strengths and elongation of the hybrid nanocomposite increased and decreased by increasing the number of ARB cycle and reached to a maximum value of 204.5Mpa and 6.1% at the end of 9th cycle, respectively.

Deep rolling is a powerful tool to increase the service life or reduce the weight of railway axles. Three fatigue-resistant increasing effects are achieved in one treatment: lower surface roughness, strain hardening and compressive residual stresses near the surface. In this work, all measurable changes introduced by the deep rolling process are investigated. A partly deep-rolled railway axle made of high strength steel material 34CrNiMo6 is investigated experimentally. Microstructure analyses, hardness-, roughness-, FWHM- and residual stress measurements are performed. By the microstructure analyses a very local grain distortion, in the range < 5 µm, is proven in the deep rolled section. Stable hardness values, but increased strain hardening is detected by means of FWHM and the surface roughness is significantly reduced by the process application. Residual stresses were measured using the XRD and HD methods. Similar surface values are proven, but the determined depth profiles deviate. Residual stress measurements have generally limitations when measuring in depth, but especially their distribution is significant for increasing the durability of steel materials. Therefore, a numerical deep rolling simulation model is additionally built. Based on uniaxial tensile and cyclic test results, examined on specimen machined from the edge layer of the railway axle, an elastic–plastic Chaboche material model is parameterised. The material model is added to the simulation model and so the introduced residual stresses can be simulated. The comparison of the simulated residual stress in-depth profile, considering the electrochemical removal, shows good agreement to the measurement results. The so validated simulation model is able to determine the prevailing residual stress state near the surface after deep rolling the railway axle. Maximum compressive residual stresses up to about -1,000 MPa near the surface are achieved. The change from the induced compressive to the compensating tensile residual stress range occurs at a depth of 3.5 mm and maximum tensile residual stresses of + 100 MPa at a depth of 4 mm are introduced. In summary, the presented experimental and numerical results demonstrate the modifications induced by the deep rolling process application on a railway axle and lay the foundation for a further optimisation of the deep rolling process.

Finite element method and bending experiments were carried out to survey the influence of bending radius on forming quality of H62 brass tubes in free bending process，which are widely used as key components of pipeline system in aerospace, aviation and automotive fields. Different bending radiuses ranged from 45 mm to 100 mm with an interval of 5 mm were employed to survey the forming defects. The results illustrated that both cross-section distortion and wall thickness variations at sections with angles in range of 10–20° and 160–170° were larger than other regions. The severe deformation behaviors usually occurred at the end of the tubes. Moreover, similar to the variation tendency of cross-section distortion, the changing of wall thickness decreases gradually with the increase of bending radius. Furthermore, the positions with the severer forming defects gradually moved towards to two terminals of the tubes with increasing bending radius. The variations of these deformation behaviors were mainly caused by the tangential stress and axial stress which were decomposed by an extra thrust introduced by the bending die. Based on the above force analysis and experimental results, the credible analytical equations were derived to quantify the effect of bending radius on forming precision during the practical bending process.

The forming behaviour of a unidirectional non-crimp fabric (UD-NCF) consisting of polyamide stitches with a tricot-chain stitching pattern is explored. Notably, there are no stabilising tows orientated transverse to the main tow direction in this fabric, a common feature in many ‘quasi’ UD-NCFs, this allows extension of the stitch in the transverse direction under certain loading conditions. The lack of stabilising tows introduces a possible low-energy deformation mode to the UD-NCF, which is absent in biaxial fabrics and to a large extent in ‘quasi’ UD-NCFs. The in-plane shear behaviour is initially investigated using both standard ‘tightly-clamped’ picture frame tests and uniaxial bias extension tests. Preliminary results show a dramatic difference in results produced by the two test methods. During the picture frame test, fibres can be subjected to unintended tension due to sample misalignment in the picture frame rig. To mitigate error arising from this effect, the picture frame test procedure is modified in two different ways: by using an intentional pre-displacement of the picture frame rig, and by changing the clamping condition of test specimen. Results show that the modified picture frame test data contain less error than the standard ‘tightly-clamped’ test but also that the shear stiffness of the UD-NCF is notably lower when measured in the bias extension test compared to the picture frame test, mainly due to the difference in loading conditions imposed during the two tests.

The components’ lightweighting has been pursued, especially in the transport industry, for greenhouse gas reduction. Topology optimization, being able to allocate the material within a provided design space, is a mathematical method that can support the design of lightweight components, preserving, at the same time, their mechanical performances. In this paper, a standard shape of a component, specifically an automotive bracket, was topology optimized by estimating the impacts of the new designs from an eco-friendly point of view. A subtractive, an additive and a casting manufacturing process were considered as possible manufacturing routes achieving an optimized geometry of the component for each of them. The topology optimizations were performed considering each processes’ peculiarities, introduced as constraints. Same strength for a given set of loads and boundary conditions was the target of each analysis. The component’s lightening can be considered environmentally friendly just after assessing the impacts associated with all the stages of the product’ life cycle. Indeed, each phase of the product’ life cycle can be affected, differently, by the performed topology optimization taking into account the peculiarities of the employed manufacturing process. The overall considerations on the most environmentally safe strategies can, therefore, change according to the specificities of the optimized shapes. The topology optimization showed its utmost potentiality, from a sustainable point of view, if applied to additive manufacturing techniques for the advantages arisen by the capability to manufacture complex shapes benefiting also of reduction time process owing to less material to be deposited.