Material Form Research Articles

Effect of continuous and discontinuous non-proportional loadings on formability of DX54 sheet material

Both continuous and discontinuous non-proportional loadings occur in multi-stage automotive stamping processes. Discontinuous loading is widely studied, but due to requiring sophisticated experimental procedures, continuous loading has been studied less. This study explores the impact of continuous loading on DX54 steel utilising an innovative experimental setup that enabled cruciform samples to undergo uniaxial to biaxial strain path change continuously without unloading. A similar two-stage discontinuous loading from uniaxial to biaxial with unloading in between was generated in DX54 to understand the differences in macro-strain, micro-strain, microstructure, and micro-texture evolution between the continuous and the discontinuous loadings. The stress state of the material during continuous loading was different to that during discontinuous loading. In this study, the occurrence of ‘pseudo-localisation’ was observed during continuous loading, and the observed rotation of high-strain bands differed between continuous and discontinuous loading. The discontinuous loading induced a higher strain, hardening rate, and increased elongation compared to the continuous loading. These results suggest the potential for higher formability during the discontinuous loading compared to the continuous loading.

Evaluating the Plastic Anisotropic Effect on the Forming Limit Curve of 2024-T3 Aluminum Alloy Sheets Using Marciniak Tests and Digital Image Correlation

This study thoroughly investigates the influence of anisotropy on the formability of 2024-T3 aluminum alloy sheets using advanced techniques such as digital image correlation (DIC) and Marciniak tests. A key finding is the relatively small variation in anisotropy values across different strain paths and orientations, contrasting with more significant variations reported in other studies. Tests were conducted on nine samples with various geometries to induce specific strain paths, including uniaxial, plane, and balanced biaxial strains, oriented in different directions relative to the rolling direction. The study also provides a detailed analysis of microstructural and mechanical characteristics, such as precipitate distribution and anisotropy behavior, which are crucial for understanding the relationship between microstructure and material formability. The results show that while anisotropy impacts deformation capacity, the differences in formability among the directions were minimal, with slightly greater formability observed in the diagonal direction. These findings are compared with forming limit curves (FLCs), offering an integrated view of how relatively uniform anisotropic properties influence formability. These insights are essential for optimizing the processing and application of 2024-T3 alloy in industrial contexts, emphasizing the importance of understanding anisotropy in the design of metal components.

Efficient formability in Radial-Shear Rolling of A2024 aluminum alloy with screw rollers

The Radial-Shear Rolling (RSR) process, commonly utilizing traditional conical rollers, encounters challenges in achieving optimal deformation in high-strength aluminum alloy A2024, vital for aerospace applications due to its exceptional strength-to-weight ratio. This study explores the potential of screw rollers to enhance RSR efficiency for A2024 aluminum, aiming to evaluate their impact on microstructure, mechanical properties, and key deformation parameters (force, temperature) compared to conical rollers. Employing a combined approach of finite element simulations and experiments with force analysis, the study assesses the effects of screw rollers in a two-pass RSR process. The findings reveal significant advantages with screw rollers, achieving a 15 % increase in equivalent strain compared to conical rollers, indicating enhanced material formability. Consistent temperature distribution across roller types ensures stable processing conditions. Screw rollers also demonstrate a 9 % reduction in force required during the second rolling pass, potentially reducing equipment load demands and enabling higher compression per pass for improved process efficiency. Additionally, a more uniform microhardness distribution suggests consistent mechanical properties with screw rollers compared to conical ones. These results highlight the potential of screw rollers to optimize RSR of A2024 aluminum, offering improved plastic deformation efficiency, temperature control, and potentially lower equipment loads. This advancement holds promise for a more efficient and cost-effective RSR process in producing high-quality A2024 aluminum components for aerospace and other demanding applications.

Synchronous improvement in strength and ductility of Cu-bearing stainless steels through formation of bimodal grain structure induced by short-time electric pulses

Excellent strength and favorable formability are two important mechanical properties of stainless steel, but there is usually a trade-off between both properties. However, it has been suggested in recent studies that preparing microstructures with a non-homogeneous structure can effectively achieve strength-ductility synergy. Given these facts, a microstructure with bimodal grain structures was prepared in this study by short-time electric pulse treatment (EPT). Besides, the evolution of microstructures and mechanical properties of Cu-bearing stainless steel during EPT was analyzed. The results demonstrated that the non-uniform heating in the EPT process can rapidly promote localized grain growth, thus forming a bimodal grain structure compared with conventional heat treatment. The microstructure of the fine grains formed random textures, while the coarsened grains showed stronger textures. After EPT, the amount of S {123} < 634 < 634 >-type textures increased significantly, with the proportion reaching up to 30.1 %. There was also a certain amount of brass {110} < 112 >- and copper {112} < 111 >-type textures. Compared with the solution-treated samples, the best overall mechanical properties were detected under the optimal electric pulse parameters, which ultimately realized a synergistic increase of 11.8 % and 10.2 % in the ultimate tensile strength and ductility. The excellent strength-ductility synergy was closely related to heterogeneous deformation-induced (HDI) strengthening and textures induced by the bimodal grain structure. This finding may provide novel insights for enhancing the formability of biomedical metallic materials.

Failure analysis and formability improvement of GLARE laminates in warm active hydroforming technology: Experimental and numerical approach

Warm hydroforming shows considerable promise as a forming technology for Fiber Metal Laminates (FMLs) parts due to its capacity to enhance the formability of materials. However, a detailed investigation into the failure behavior during hydroforming is still lacking. In this paper, a systematic experiment was performed to analyze the possible failure modes for GLARE in warm active hydroforming. Five main defect modes have been identified, including fiber crack, combined Al & fiber crack, wrinkle, low resin, and voids defects. The related formation mechanisms have been analyzed based on both experiments and numerical methods. Additionally, the effects of critical process parameters, including the blank holder force (BHF), liquid pressure rate (PR), and temperature (T) on failure behavior are thoroughly investigated and quantified. The use of step-loading BHF was recommended to enhance formability, which caused a nearly 36% decrease in the prepreg tensile damage criteria coefficient. Conversely, decreasing PR or increasing T significantly improved the formability of GLARE but resulted in low resin content and significant void defects. Consequently, a feasibility map that quantified the BHF and liquid pressure effects on various defects was developed, leading to optimized parameters for manufacturing a box-shaped part. This study not only explores the failure model of FMLs but also offers valuable insights for process parameter improvement and how to optimize key parameters in engineering processes.

On the Enhancement of Material Formability in Hybrid Wire Arc Additive Manufacturing

This paper is focused on improving material formability in hybrid wire-arc additive manufacturing comprising metal forming stages to produce small-to-medium batches of customized parts. The methodology involves fabricating wire arc additive manufactured AISI 316L stainless steel parts subjected to mechanical and thermal processing (MTP), followed by microhardness measurements, tensile testing with digital image correlation, as well as microstructure and microscopic observations. Results show that mechanical processing by pre-straining followed by thermal processing by annealing can reduce material hardness and strength, increase ductility, and eliminate anisotropy by recrystallizing the as-built dendritic-based columnar grain microstructure into an equiaxed grain microstructure.

Robust detection of ductile fracture by acoustic emission data-driven unsupervised learning

The quantitative assessment of the formability of bulk metallic materials remains challenging, primarily due to considerable difficulties in accurately identifying the initiation of fractures. This study introduces a novel methodology for detecting the onset of ductile fracture by using acoustic emission signals. Unlike traditional methods that rely on standard characteristics, this approach utilizes acoustic emission signals that are depicted through vivid and direct feature images. These images represent short-term and relative energies, which are termed as energy allocation maps. These maps are generated utilizing a novel signal processing technique that employs the maximal overlap discrete wavelet transform for multi-resolution analysis. In this study, a parameter known as accumulative relative energy is developed to illustrate the global energy distribution across resolutions, while another parameter, normalized short-term energy, is designed to capture the local energy distribution of resolutions. The natural neighbor interpolation technique is subsequently employed to derive the energy allocation map. A set of stacked autoencoders is accordingly configured to transform this map into a singular value that represents the condition of the material. Consequently, a ductile fracture indicator is proposed to identify the onset of fracture. The accuracy and efficacy of the proposed method are validated through partial experiments. The study examines four bulk metallic materials, providing insights into their deformation capabilities under compression.

Dynamic globularization behavior of the dual-phase TiZrV medium entropy alloy during hot working

Globularization is an advantageous way to improve the formability of dual-phase materials. Dynamic globularization behavior of the TiZrV medium entropy alloy (MEA) with dual-phase was investigated at the temperature range of 500 ℃ ∼ 700 ℃ and strain rate of 0.1 s-1 ∼ 10 s-1 by the double-cone compression test. The finite element software was used to simulate the hot compression process of the double-cone specimen. Transmission electron microscope (TEM) was used to study the deformation microstructure features. The double-cone test can produce a wide strain range and corresponding deformation microstructure. The highest globularization ratio of 72.4% was obtained under the strain of about 0.88 at 500 ℃ and 10 s-1. The hot deformation mechanism map in the temperature range of 500 ℃ ∼ 700 ℃ and the strain range of 0.2 ∼ 1.2 at 10 s-1 was constructed by combining the double-cone test with finite element simulation. The hot deformation mechanism map is divided primarily into two parts. At 500 ℃, in the strain region of 0.2 ∼ 0.88, the deformation mechanism is dynamic recovery (DRV), and in the strain region of 0.88 ∼ 1.2, the deformation mechanism is dynamic recrystallization (DRX). It is considered that DRX plays a key role in dynamic globularization of the TiV phase during hot working and its production is summarized.

Stretch-forming characteristics of austenitic material stainless steel 304 at hot working temperatures

Abstract The need for sheet metal forming using highly resistant materials such as titanium alloys and stainless steel has increased recently. These materials possess elevated mean flow stress values, which make them difficult to draw at room temperature. To achieve a homogeneous distribution of strain in the stretched component, reduce the load required for plastic deformation, and greatly improve material formability, hot forming is helpful. The goal of the current study is to conduct stretch-forming experiments to investigate the forming characteristics of Austenitic material Stainless Steel (ASS) 304 at Hot working temperatures. Stretch forming experiments have been conducted on the Servo electrical sheet press test machine at 650 and 800°C. The formability has been estimated by constructing a Fracture forming diagram (FFLD), limiting the height of the dome (LDH) and the distribution of the strain of stretched cups. It has been discovered that the limit of forming bounds rises with the temperature reaching 800°C, while the DSA effect causes the necking region – the area between the safe and fracture limits ‒ to decrease with additional temperature rise from 800 to 900°C. Within the experimental limitations, it has been considered that the Hot forming of ASS 304 at 650°C gives the highest strain forming limits with a uniform strain distribution in the stretched cups. From the Formability limit diagram, dome height, and strain distribution, it can be observed that ASS 304 has good limiting strain up to 800°C with lower load application.

Microstructure evolution and strengthening mechanism of pure copper sheet induced by laser shock forming

laser shock forming (LSF) is a high strain rate forming process, which can significantly improve the formability of materials. Nevertheless, there is a lack of research on the microstructure evolution and improving mechanical properties of parts deformed by LSF. In this paper, pure copper sheet are formed into flat bottom parts under one- and two-shot LSF. The deformation topography, surface morphology and thickness distribution of the deformed parts are tested. The surface micro morphology of the mould can be additionally printed in the formed parts, and the sheet forming accuracy improved continuously and lower thickness thinning with the increase of the shock number. Transmission electron microscopy (TEM) showed that the microstructure on the surface of the formed specimens was composed of nanocrystalline arrays elongated in the direction of the transverse flow of the workpiece material. The dislocation density decreased and the twinned structures gradually disappeared with an increasing depth from the treated surface. More laser shocking can refine the metal material grain and improve material mechanical property of the formed part further. Eventually, the underlying improvement mechanism of mechanical properties induced by LSF-induced microstructure evolution on pure copper was systematically revealed.

Predicting edge fracture in dual-phase steels: Significance of anisotropy-induced localization

While experimental methods for characterizing edge fracture have advanced significantly, current modeling approaches often neglect factors like anisotropy evolution and localization, limiting their ability to accurately predict edge fracture across various tests. In the present study, we investigate the anisotropic deformation, localization, and fracture behavior of a dual-phase (DP1000) steel during hole expansion tests using an advanced evolving anisotropic model coupled with a hybrid damage mechanics model. The anisotropic plasticity model is calibrated by tensile tests along different loading directions and is capable of describing both anisotropic hardening and r-value evolution, while the fracture model is calibrated by tests under several stress states. To illustrate the impact of anisotropy, an isotropic version of the model is also included for comparison. The novelty of the investigation is that it originally found the edge fracture of the DP1000 steel is anisotropic and triggered by through-thickness localization induced by material anisotropy. Therefore, only the model with anisotropy can provide a satisfactory prediction of the hole expansion ratio as well as the location of the edge fracture, while the isotropic model overestimates the experiments significantly. The findings provide an in-depth understanding of the importance of anisotropy in evaluating edge fracture behavior, which not only improves the modeling accuracy but also adds a design concept to enhance the edge formability of materials.

Anisotropic and heterogeneous acoustoplasticity of α-Ti during ultrasonic vibration assisted compression: Modeling and experiments

Introducing ultrasonic vibration (UV) into the plastic deformation process is a promising and efficient way to improve the formability of metallic materials. However, the acoustoplasticity of α-Ti with pronounced anisotropic behavior during UV-assisted deformation is still not well understood, and the underlying mechanisms associated with the ultrasonic effect on multiple slip/twinning systems remain ambiguous. In this research, the anisotropic and heterogeneous acoustoplasticity of α-Ti was investigated through modeling and experiments. A novel acoustic crystal plasticity model considering the anisotropic ultrasonic response of multiple slip/twinning systems was proposed, in which the ultrasonic softening is determined by the coupling effect of crystal orientation, mechanical threshold, and ultrasonic energy density. The proposed model was validated through the mechanical response of the UV-assisted compression and the twin volume fraction of α-Ti specimens along RD, TD, and ND directions. Full-field crystal plasticity simulations regarding UV-assisted compression were carried out. Then the mechanism of the acoustoplasticity of α-Ti was explored via the analysis of ultrasonic activation on multiple slip/twinning systems and the grain scale deformation behavior. A considerable anisotropic and heterogeneous ultrasonic softening effect of α-Ti was found, and the anisotropy as well as the magnitude of ultrasonic softening increase with the ultrasonic energy density. The ultrasonically activated deformation modes gradually change from prismatic slip and tensile twinning to basal slip and compressive twinning from RD, TD to ND specimens, which results in a higher average CRSS decrease and more pronounced ultrasonic softening macroscopically. The grain scale stress inhomogeneity of α-Ti is relieved under UV, and the local deformation and grain rotation are both enhanced. The dislocation motion and twinning behavior are both promoted by UV. The facilitated twinning behavior can be attributed to the enhanced dislocation assisted nucleation and propagation of deformation twins under UV. These findings provide a fundamental understanding of the anisotropic and heterogeneous acoustoplasticity of α-Ti during the UV-assisted deformation process.

Flow-field design of the bipolar plates in polymer electrolyte membrane fuel cell: Problem, progress, and perspective

As a promising carbon-neutral technology, the polymer electrolyte membrane fuel cell (PEMFC) is gaining considerable attention over the past decades. Many problems in PEMFC performance and durability can be ultimately ascribed to the flow-field design, which is a complex and systematic work owing to the inherent sophisticated nature of the PEMFC with multicomponent mass transportation and multiphysics field coupling. This paper presents a critical review of the state-of-the-art flow-field designs and an in-depth analysis of the key problems involved from a perspective of efficient mass transport within the PEMFC. In particular, flow-optimization principles are discussed specifically for the enhancement in reactant mass transfer, water management, optimized opening ratio, uniformity of flow distribution, and choice of appropriate numerical approaches assisting the flow-field design. The material formability and forming accuracy and their effects are also discussed for metallic bipolar plates. The objective of this review work is to present a comprehensive overview of the problems, progresses, and perspectives of the flow-field designs for bipolar plates in PEMFC and provide a general theoretical instruction for present and future relevant R&D activities that aim at high-performance, durable, and low-cost fuel cells.

Fracture forming limit curve prediction by ductile fracture models

The fracture forming limit curve is an essential tool giving information about fracture initiation in metal forming applications. In order to obtain a fracture-forming limit curve, the Nakajima test should be carried out. However, these tests are costly and time-consuming processes. Therefore, companies in the automotive industry tended to use non-expensive numerical approaches to determine the material's formability limits. In this work, an anisotropic polynomial yield criterion was implemented to calibrate the different ductile fracture models, including only or both the stress triaxiality and the Lode parameter's effect. Analyses of different uniaxial tensile test geometries were carried out, and the two-dimensional fracture loci were constructed by different ductile fracture models. Correspondingly, the fracture-forming limit curves were predicted by the two-dimensional fracture loci. The results showed that the ductile fracture models, including only the stress triaxiality effect, provide an acceptable performance covering the range from uniaxial tension and the plane strain tension lines, while the models, including the stress triaxiality and Lode parameter, provide a plausible prediction performance throughout the whole range for forming limit diagram.

Experimental Material Characterization and Formability studies on Aluminium Alloy (AA 8011)

Operations for sheet metal shaping are essential to the production of many different kinds of goods. But there is still a problem with plastic fragility in this industry, which frequently results in faulty goods. To solve this problem during production, it’s critical to take into account a number of factors, including the Forming Limit Diagram (FLD). In this work, the formability of the Aluminum Alloy (AA8011) at strain rates of 0.01 mm/s at ambient temperature, 100 °C, and 150 °C has been investigated. The Nakajima test was used to execute stretch forming in order to achieve the study’s results. The material’s restricting stresses increased as temperatures increased, according to the outcomes, which were examined utilizing fractography investigations carried out under a scanning electron microscope and simulations carried out with LS-dyna software. This work will help create more productive and successful sheet metal-forming techniques by offering insightful information on the formability of AA 8011 sheet at extreme temperatures.

Experimental Study and Neural Network Model to Predict Formability of Magnesium Alloy AZ31B

Magnesium alloy is an emerging smart metal used in various industries like automotive and aerospace industry, due to their lightweight and excellent strength-to-weight ratio. Formability, a critical factor in manufacturing processes, determines the alloy’s ability to undergo deformation without fracture or defects. Fuel economy and environmental conservatives are the key desirable factors in selection of magnesium alloy sheets. Magnesium alloy sheets have low formability at room temperature due to their hexagonal closed-packed microstructures. As the magnesium’s formability at room temperature is considerably low, stretch forming tests are conducted at moderate temperatures. For this purpose, commercially available AZ31B magnesium alloy sheet of 1.1mm thickness has been used and tested at room temperature, 25 degree to within medium temperatures range and at a higher strain rate of 0.01/s. The main objective of an experimental study to predict the formability of magnesium alloy sheets is to gather data through controlled tests and measurements. This data and Forming Limit Diagram (FLD) can be used to analyse the formability of material, it defines failure criteria. On the other hand, using a neural network to predict formability involves training the network on the collected experimental data. Once trained, the neural network can predict the formability of new magnesium alloy sheets based on their characteristics, offering a faster and potentially more accurate prediction method compared to traditional models. This work explores into the realm of regression modelling utilizing neural networks, a powerful subset of machine learning techniques. It begins with a discussion on the setup of machine learning models, emphasizing the crucial steps involved in data preprocessing, model selection, and evaluation.

Experimental investigation and numerical optimization of sheet metal forming limits during deep drawing process of DD14 steel

This work aims to experimentally study the deep drawability of DD14 hot-rolled steel sheets and to optimize numerically the material formability. The material anisotropy was confirmed by metallographic analysis of the material and tensile tests on specimens taken in three orientations with respect to the sheet rolling direction. Where the stress-strain curves show a sensitivity of material to the Piobert-Lüders phenomenon. The die pressure and the blank holder were considered as controlling factors on plastic instability and the success of the deep drawing operation. The forming limit curves (FLC) were plotted to highlight the different deformation modes that the sheet metal underwent during the deep drawing process. The collected deep-drawn parts observation shows severe plastic instability, until fracture. The initial plastic anisotropy is determined by the Hill48 quadratic criterion and the work hardening by the Hollomon power law. It results, during the experimental tests, that the front bottom corners of the deep drawn part are the areas at high risk of damage. The various numerical simulation scenarios followed by comparisons with the experimental results, allowed us to confirm the optimum conditions that minimize the material's plastic instability risks, forming operation “Step” and BHP “Amplitude”.

Study on the formability of copper foils during multi-step micro deep drawing

In this work, the formability of copper foils was analyzed based on a series of multi-step micro deep drawing (MMDD) tests. The copper foils were annealed at temperatures ranging from 300 to 700 °C for 5 min, followed by tensile tests and electron backscatter diffraction (EBSD) tests for the exploration of mechanical behavior and microstructural characterization of annealed specimens. The results show that the as-received copper foils exhibit poor formability and cannot form micro cups during MMDD. When the annealing temperature attains 500 °C, a homogeneous microstructure was formed inside copper foils, enhancing the formability of materials and improving the surface quality of formed products. Nevertheless, both the elongation and tensile strength decrease dramatically due to the easy occurrence of incoordination deformation in coarse grain bands with further increase in annealing temperature to 700 °C. Consequently, marked wrinkling is generated on the surface of drawn cups and obvious thinning occurs at the nose radius region due to metal flow. In addition, the results show that the E texture component within the copper foils is favorable for MMDD. Overall, an optimal annealing temperature of 500 °C is obtained with improved formability of copper foils and forming quality of drawn cups.

Micro forming studies of SS316L as biomedical application material

The process of shaping flat sheets of metal into necessary shapes without any flaws is known as sheet metal making. Nowadays, there is a growing demand for micro goods and microdevices due to the popularity of miniaturization across many industries. The manufacturing method known as micro forming creates tiny components for various en-gineering uses. Micro-forming can be found in a variety of fields, including automotive, biomedical, and aerospace engineering. Whenever the sheet material’s thickness corre-sponds to ingrained length distribution of the material being used during the micro-forming process, the deformation behavior is different from what is anticipated for the macroscopic sheet material. A material's ability to be formed is one of the crucial pro-cesses, and one of the crucial parameters for determining a material's formability is its forming limit curve or as forming limit diagram. The purpose of this study is plotting Forming Limit Curve for specific biomaterial using numerical simulation and experimenta-tion. For the purpose of determining the forming limit curves, a controlled experiment of thin SS316L sheet of 60 µm thickness with different angles in relation to rolling directions (0°, 45°, 90°) is conducted in the present research. In accordance to ASTM-2218-14 standard test, Nakajima test for micro-forming is done using a specimen of uniaxial, uni-axial intermediate, plane, biaxial intermediate and biaxial strain paths to measure limiting strains. The limit diagram for SS316L is formed using the numerical software Simufact Forming V15, and the findings are then compared with the Nakajima test. The compari-sons between the experimental method with the numerical simulations show good ac-cordance. It was shown that FLC produced by numerical simulation are designed to be 5 % to 12 % less than experimental work and are safe. To examine the physics of the sheet, micro structural studies are also carried out on the test object both prior to and after form-ing. The microstructural study explains the characteristics of the sheet.

Tough and Moldable Sustainable Cellulose-Based Structural Materials via Multiscale Interface Engineering.

All-natural materials derived from cellulose nanofibers (CNFs) are expected to be used to replace engineering plastics and have attracted much attention. However, the lack of crack extension resistance and 3D formability of nanofiber-based structural materials hinders their practical applications. Here, a multiscale interface engineering strategy is reported to construct high-performance cellulose-based materials. The sisal microfibers are surface treated to expose abundant active CNFs with positive charges, thereby enhancing their interfacial combination with the negatively charged CNFs. The robust multiscale dual network enables easy molding of multiscale cellulose-based structural materials into complex 3D special-shaped structures, resulting in nearly twofold and fivefold improvements in toughness and impact resistance compared with those of CNFs-based materials. Moreover, this multiscale interface engineering strategy endows cellulose-based structural materials with better comprehensive performance than petrochemical-based plastics and broadens cellulose's potential for lightweight applications as structural materials with lower environmental effects.