Uniform Strain Distribution Research Articles

Linear strain gradient-regulated bifurcation of circular bilayer plates

Bilayer structures with controllable self-folding capability have found applications in a variety of cutting-edge fields such as flexible electrics, wearable devices and soft robotics. The folding of bilayer structures occurs when the mismatch strain between the two layers exceeds the bifurcation threshold, resulting in a deformation transition from an axisymmetric to a folded state. Previous efforts have predominantly focused on bilayer structures with uniform and/or anisotropic strain distributions. However, the role of non-uniform in-plane strain distributions in regulating the bifurcation of bilayer structures has not been fully understood. In this study, the effects of linear in-plane strain gradients on the bifurcation of circular bilayer plates, both with and without geometric mismatch, are systematically investigated by combining theoretical analysis, finite element simulations and experiments. Our results reveal that both the mismatch strain gradient and the geometric mismatch between the two layers play crucial roles in regulating bifurcation. Notably, linear mismatch strain gradients with larger strain at the center delay bifurcation, while those with larger strain along the edge promote bifurcation. This work offers new insights into the design of controllable self-folding bilayer structures, which is of great significance for advanced applications.

Investigation on the biaxial stretching deformation mechanism of PA6 film based on finite element method

Abstract This study employed the finite element method to investigate the biaxial stretching deformation mechanism of polyamide 6 (PA6) Film. First, the PA6 film was subjected to biaxial stretching experiments under various conditions. Then, a three-dimensional finite element model of PA6 film was established. The biaxial stretching experiments of PA6 films under various conditions were simulated by the established finite element model. The results show that the biaxial stretching of the films under various conditions exhibited a transition from elastic deformation to plastic deformation. Meanwhile, as the stretching ratio increases, the more uniform stress and strain distribution on the film surface can be found in the stress and strain contour diagrams. The stress and strain distributions were found to be largely consistent under various annealing temperatures. However, lower stretching rates resulted in higher internal stress intensity, making the films more resistant to biaxial stretching. The findings of this study provide a theoretical reference for a deeper understanding of the deformation mechanisms of PA6 films during the biaxial stretching process.

Mechanical properties, nano-tribological behavior and deformation mechanism of FeCrNi MEA with the addition of Co/Cu: Molecular dynamics simulation

During manufacturing processes, alloys face increasingly demanding requirements for their mechanical and tribological properties, underscoring the importance of revealing their deformation mechanisms. This study employed molecular dynamics simulation to construct models of FeCrNi (C1), FeCoCrNi (C2), FeCrNiCu (C3), and FeCoCrNiCu (C4), investigating the tribological properties of C1 alloy under various conditions and the mechanical properties across a wide temperature range (223–1073 K). The results indicate that the elastic modulus of the alloys follows the order C2 > C4 > C3 > C1 across the temperature range of 223 K to 1073 K. The elastic modulus increases with rising temperatures and decreases before rising once again as temperatures decrease. The phase transitions become more pronounced below 300 K. The addition of Co elements to the FeCrNi alloy contributes to fine-grain strengthening, uniform distribution of internal stress and strain, reduction in local stress concentration, and improvement of the alloy ductility and tensile strength. Compared to sliding friction, rolling friction reduces the number of worn atoms; however, the tensile and shear effects cause an increase in the stress gradient, leading to more severe subsurface damage and shear deformation. Temperature significantly affects the tribological properties of the alloys: phase transitions at high temperatures promote dislocation slip and plastic deformation, while at low temperatures, higher hardness and strength are observed. The roughness of stacking faults is greatly influenced by temperature, with an increase at the low-temperature range (223–273 K), a decrease in the mid-temperature range (273–673 K), and a smoother surface at the high-temperature range (673–1073 K). The research aims to provide a deeper understanding of the excellent mechanical and tribological properties of FeCrNi alloy at the micro/nano scales, thereby advancing their application and development in manufacturing processes.

Design and experimentation of width tapered meandered array structure for low frequency broadband vibration energy harvesting

A novel 6DoF Tapered beam energy harvester, capable of operating across a broad and low frequency range, is proposed in this work. The hybrid structure incorporates regular beam array and zig-zag sections, enhancing deformation and bending. Width tapering with constant thickness optimizes the structural performance and energy harvesting capabilities of the beam. Tapering ensures even strain distribution, reducing the risk of structural failure. The proposed structure demonstrates wide band characteristics at low frequencies, delivering higher power output compared to an array of cantilevers for a given area. FEM analysis is conducted to optimize proof mass, aiming for closely spaced resonance frequencies and high-power output. Experimental validation on a prototype confirms the accuracy of the frequency response predicted by the models. Under harmonic base excitation of 0.4 g, the harvester yields an average DC power of 2497 μW, accounting for signal conditioning losses, within the frequency range of 9–20 Hz. The suggested structure offers excellent design flexibility, allowing adjustment of resonant frequencies by varying the number of beams, the slope and the proof mass of individual beams. The geometry of the proposed structure provides versatility, mechanical resilience, uniform strain distribution make it suitable for developing MEMS energy harvesters.

High-temperature fretting wear behavior and microstructure stability of a laser-cladding Ti-Al-C-N composite coating meditated by variable cycle conditions

Ti-6Al-4 V titanium alloy is used for low-pressure compressor blades of aero-engine due to its high specific strength, excellent corrosion resistance and high-temperature stability. Low-pressure compressor blades are subject to fretting wear in service, which may lead to fracture failure of the blades. The preparation of wear-resistant coatings is currently an effective solution in solving the problem of fretting wear on Ti-6Al-4 V titanium alloy. However, the fretting wear resistance and microstructure stability of the coating under variable cycle fretting conditions require more attention. In this work, the fretting wear performance and microstructure stability of the Ti-Al-C-N composite coating under variable cycle fretting conditions are investigated. The results show that the parameters of variable cycle operating conditions have a notable effect on the coefficient of friction (COF). The variable frequency and variable temperature working conditions result in the alteration of the fretting operation mechanism. Whereas the variable stroke amplitude and the variable load conditions do not cause changes in the fretting operation mechanism, and both are in the gross slip region (GSR). The lowest wear rate occurs under variable stroke amplitude conditions. The wear rate is the maximum under the variable cycle temperature condition. According to the dissipated energy calculation, the difference between the two different stroke amplitudes is the biggest among all the conditions. EBSD and TEM analyses show that the subsurface of variable stroke amplitude worn scar has a more uniform strain distribution, and reveals a unique subsurface structure with a transformation from crystalline to amorphous, which contributes to improving the wear resistance. This work provides insights into coating microstructure stability and wear mechanisms under variable cycle conditions.

Numerical Investigation of Piezoelectric Energy Harvesting From a Multi-Mode T-Shaped Structure

In this work, energy harvesting from a proposed three-mode T-shaped structure, composed of a vertical beam, two horizontal beams, a center mass, and tip masses, is investigated to expand the frequency bandwidth for energy harvesting, without compromising the power density due to the additional mass of the structure, as is the case with most multi-mode harvesters. The aim is to cleverly use and position the additional mass to help induce higher and more uniform strain levels throughout the piezoelectric patch, leading to greater power generation to help counteract the added mass. A numerical model was developed to analyze the structure, to obtain voltage and power frequency responses, taking into effect the load resistance modeling and the accurate evaluation of resonance peaks by estimating each mode damping ratio. The validity of the model was confirmed by comparisons with previous experiments involving other structures, which demonstrated strong agreement. The excitation load was strategically applied to induce maximum displacement of the center and tip masses relative to the fixed ends in each mode. The outcomes reveal that the T-shaped configuration exhibits the capacity to generate higher maximum strain and a more uniform strain distribution across the piezoelectric patch when compared to previous L-shaped and traditional cantilever harvesters' designs. These characteristics yielded a power density higher than that of the L-shaped structure by approximately 70% with only around 20% addition in structure mass. Additionally, the multi-mode T-shaped structure boasts a significantly broader harvesting bandwidth due to the additional mode, without compromising power density, as was the case with L-shaped structures. Furthermore, the positioning of the tip mass was systematically altered to assess its impact on the frequency bandwidth and power output of the horizontal and vertical beams in the three bending modes, demonstrating great robustness and tuning capabilities.

Grain boundary-mediated strain response mechanism of AZ31 gradient- structure Mg alloy plate under uniaxial tensile loading

The changes in strain gradient induced by grain boundaries are crucial for enhancing the plasticity of gradient magnesium (Mg) alloys. The change of strain distribution influence by grain boundaries during plastic deformation of the gradient structure was examined. In this paper, the gradient structure AZ31 Mg-alloy plate with the surface fine grain (FG) to the center coarse grain (CG) was fabricated using hard plate rolling (HPR). The microstructure and strain distribution of Mg-alloy with a gradient structure were analyzed by electron backscatter diffraction (EBSD) and Digital image correlation (DIC) during uniaxial tensile. The findings indicate that the gradient structure sample (GS sample) displays a uniform strain distribution during the tensile process. Coarse-grain sample (CG sample) have obvious strain concentration, which leads to premature fracture. Based on EBSD characterization, low-angle grain boundaries (LAGBs) accumulates in the CG during plastic deformation. Orientation of CG tends to the (0001) basal. At the same time, the density of geometrically necessary dislocations (GNDs) inside CG has changed, which improves the Heterogeneous deformation induced (HDI) stress of gradient structure. During the uniaxial tensile, LAGBs accumulates in CG and changes the strain distribution of the gradient structure, which induces the accumulation of GNDs, and hence improving the properties of the GS Mg-alloy. These findings unveil the mechanism of strength-plasticity synergism of GS alloys from a new perspective and offer insights into the application of GS in Mg-alloys.

Shear deformation behavior of additively manufactured 316L stainless steel lattice structures

With the development of additive manufacturing, lattice structures have emerged as a disruptive technology across various fields, including aerospace, automotive, and defense. Lattice structures exhibit exceptional properties for lightweight and energy absorption capacities, especially under compressive loads. However, the lack of experimental data on complex loads, such as shear properties of lattice structures, poses challenges to their broader application across different load types. This study aims to analyze the shear deformation behavior of lattice structures and compare them with their compressive properties, enabling the safe design of lattice structures for various load applications. To achieve this, 316 L stainless steel lattice structures were fabricated using additive manufacturing in three different geometries: body-centered cubic (BCC), face-centered cubic (FCC), and octet truss (OCT), all at the same relative density. The lattice geometries were compared for their mechanical properties and deformation mechanisms under the two types of loading using DIC and FEM analyses, compression and shear tests. It was found that the mechanical properties of the lattice structures under compression and shear loads varied depending on the geometry, showing that each lattice geometry has a unique load-bearing capacity that exhibits superior mechanical properties. Furthermore, under shear loading, the struts of the BCC lattice structure showed a bending-dominated deformation mode due to the rotation of the nodes, whereas the struts of the FCC and OCT structures presented a compression and tension-dominated deformation mode. As a result, the BCC lattice specimens showed a higher shear energy absorption capacity than the other specimens and were capable of bearing higher loads. In addition, the FCC specimens showed lower shear energy absorption. The OCT specimens presented a uniform strain distribution under both compression and shear loading and showed compliant performance. The shear deformation behavior of various lattice structures has been evaluated by considering both geometrical and local strain distribution aspects. Implications for optimization guidelines and potential improvements were also discussed. These results can be used for research and development of the shear properties of lattice structures, the safe design of lattice structures, and industrial applications.

Stereointerface Structure Drives Ferroelectricity in BaZrO3 Films.

Interfacial strain engineering can induce structural transformation and introduce new physical properties into materials, which is an effective method to prepare new multifunctional materials. However, interfacial strain has a limited spatial impact size. For example, in 2D thin films, the critical thickness of biaxial strain is typically less than 20 nm, which is not conducive to the maintenance of a strained structure and properties in thick film materials. The construction of a 3D interface can solve this problem. The large lattice mismatch between the BaZrO3 thin film and the substrate can induce the out-of-phase boundary (OPB) structure, which can extend along the thickness direction with the stacking of atoms. The lattice distortion at the OPB structure can provide a clamping effect for each layer of atoms, thus expanding the spatial influence range of biaxial strain. As a result, the uniform in-plane strain distribution and strain-induced ferroelectricity (Pr = 13 μC/cm2) are maintained along the thickness direction in BaZrO3 films.

Microstructure and mechanical behavior in a spherical L12 nanoprecipitates strengthened Ni35Co27.5Cr27.5Al5Ti5 high-entropy alloy fabricated by direct casting and heat treatment

Intricate thermomechanical processing (TMP) including casting, homogenization, cold rolling, annealing and aging, has been widely used to achieve L12-strengthened CoCrNi-based medium- and high-entropy alloys (MEAs/HEAs). However, a large number of parts are usually manufactured by direct casting. We fabricated a non-equiatomic Ni35Co27.5Cr27.5Al5Ti5 HEA consisting of spherical L12 nanoprecipitates and FCC matrix using casting, homogenization and aging. Notably, both the homogenized and aged Ni35Co27.5Cr27.5Al5Ti5 HEA samples exhibit equiaxed grains, with the latter showcasing uniformly distributed spherical L12 nanoprecipitates in the FCC matrix. The average size and volume fraction of these nanoprecipitates in the aged HEA are ∼10.9 nm and ∼41.9 vol%, respectively. Mechanical testing reveals remarkable improvements in the aged HEA, with a yield strength of ∼916 MPa, an ultimate tensile strength of ∼1220 MPa, and a total elongation of ∼21.5 %. The observed enhancement is primarily attributed to precipitation strengthening mechanism. Digital image correlation (DIC) analysis of tensile deformation demonstrates uniform strain distribution in both the homogenized and aged HEA samples. In addition, electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM) examinations unveil a complex interplay of deformation mechanisms, including multiple planar slip, dislocation shearing coherent L12 precipitates, superpartials, stacking fault (SF) networks, and Lomer-Cottrell (L-C) locks. These mechanisms collectively impede dislocation motion, thereby contributing to the excellent strain-hardening ability and outstanding strength-ductility synergy of the HEA.

Microstructural Evolution and Mechanical Properties of Cast Al–2.6Li–2.8Mg–(0.5, 1.4)Cu–0.2Zr–0.2Sc Alloys during Heat Treatment

Cu is commonly used to improve the mechanical properties of Al–Li alloys, but its exact role in multicomponent Al–Li alloys is not fully understood. Herein, the microstructure and mechanical properties of two cast Al–2.6Li–2.8Mg–(0.5, 1.4)Cu–0.2Zr–0.2Sc (wt%) alloys aged at 165 °C are compared. The results show that Alloy 1.4Cu possesses finer grain size and better mechanical properties than Alloy 0.5Cu. The δ′ (Al3Li), Al3(Sc, Zr, Li) phases, and Guinier–Preston–Bagaryatsky zones are formed in both alloys. During the early stage of ageing (8 h), many dispersed S′ (Al2CuMg) phases precipitate only in Alloy 1.4Cu and coarsen continuously. Instead, many rod‐shaped S1 (Al2MgLi) phases start to precipitate in Alloy 0.5Cu up to ageing for 32 h and then coarsen continuously with ageing. Moreover, Alloy 1.4Cu shows narrower δ′‐precipitate‐free zones along grain boundaries than Alloy 0.5Cu. The higher strength and ductility with more uniform strain distribution for Alloy 1.4Cu than Alloy 0.5Cu is attributed to finer grain size and unique phase formation for the former.

Strain for toughened epoxy resin composites for GIL tri‐post insulators under tension and electric fields

AbstractToughening plays a key role in epoxy resins (EPs) and their composites for high voltage gas‐insulated switchgear (GIL) tri‐post insulators and receives a lot of attention. However, there are still limited research studies on strain and its distribution for the toughened EPs and composites under tension and especially under high electric fields. Herein, the intrinsically toughening mechanism of EPs (toughening ability: EP‐B > EP‐A) and their composites with Al2O3 (toughening ability: EP‐Bcom > EP‐Acom) was explored in terms of chemical characterisation by IR and molecular motion via differential scanning calorimetry and dielectric spectra. A low rigid segment content in EPs contributes to the excellent toughness. Two‐dimensional digital image correlation (2D‐DIC) and three‐dimensional DIC (3D‐DIC) were utilised to probe strain and its distribution in EPs and their composites under tension and electric fields, respectively. EP‐B with more toughness endows it with a larger strain εF under tensile fields and a greater strain amplitude |εE| under electric fields than EP‐A, such as 9278 με at 1 kN, 16.9% greater than EP‐A and 9767 με at 10 kV/mm, 19.3% higher than EP‐A. In addition, all samples show minus strain under electric fields due to compression. With the introduction of Al2O3, EP‐Bcom exhibits a εF of 2870 με at 1 kN, 69.1% lower than that of EP‐B and 49.4% greater than that of EP‐Acom, and it provides |εE| of 5351 με at 10 kV/mm, 45.2% lower than that of EP‐B and 13.2% greater than that of EP‐Acom. Further, samples with more toughness deliver more uniform strain distribution whether under tension or electric fields.

Association analysis of antibiotic and disinfectant resistome in human and foodborne E. coli in Beijing, China

The widespread use of chemical disinfectants and antibiotics poses a major threat to food safety and human health. However, the mechanisms of co-transmission of antimicrobial resistance genes (ARGs) and biocides and metal resistance genes (BMRGs) of foodborne pathogens in the food chain is still unclear. This study isolated 343 E. coli strains from animal-derived foods in Beijing and incorporated online data of human-derived E. coli strains from NCBI. Our results demonstrated a relatively uniform distribution of strains from various regions in Beijing, indicating a lack of region-specific clustering. Additionally, predominant sequence types varied between food- and human-derived strains, suggesting a preference for different hosts and environments. Phenotypic association analysis showed that the chlorine disinfectants peroxides had a significant positive correlation with tetracyclines. Many more ARGs and BMRGs were enriched in human-associated E. coli compared with those in chicken- and pork-origin. The quaternary ammonium compounds (QACs) resistance gene qacEΔ1 had a strong correlation with aminoglycoside resistance gene aadA5, folate pathway antagonist resistance gene dfrA17, sul1 and macrolide resistance gene mph(A). The correlation results indicated a significant association between the copper resistance gene cluster pco and the silver resistance gene cluster sil. Coexistence of many resistance genes was observed within the qacEΔ1 gene structure, with qacEΔ1-sul1 being the most common combination. Our findings demonstrated that the epidemiological spread of resistance is affected by a combination of heavy metals, disinfectants and antibiotic use, suggesting that the prevention and control strategies of antimicrobial resistance need to be multifaceted and comprehensive.

Strength of Composite Pressure Insulators for High Voltage Circuit Breakers: An Experimental and Numerical Investigation.

Glass fiber-reinforced composite cylinders, capable of withstanding internal pressure generated during service, are increasingly utilized as insulators in high voltage circuit breakers. Different testing procedures have been suggested by various standards to assess the pressure resistance of these components. Due to its simplicity and cost-effectiveness, the split-disk testing method is the most widely used for evaluating the hoop strength of pressure cylinders during the development and verification phases. However, the method presents several aspects, such as those related to the influence of specimen geometry and friction, which require further examination since they may impact the outcome of the experimental tests. The investigation, carried out by a combination of experimental testing and finite element analyses, shows that the friction between the specimen and the semi-disks has a noteworthy effect on the hoop load applied to the specimen. Almost constant load distributions along the hoop direction, representative of the real operating conditions in a pressurized cylinder, can be achieved via proper lubrication of the contact surfaces. Furthermore, FE analyses demonstrate that the notch geometry suggested by specific standards (short notch) is not capable of inducing a uniform strain distribution in the notched region. A different notch geometry (long notch) is proposed in the study to attain a more uniform strain field over the reduced area region. The experimental results indicate that the strength measured on the short notch specimens is higher than that determined on the long notch specimens, thus confirming the significant influence of strain distribution on the strength properties measured with the split-disk method.

Coupled thermomechanical finite element analysis of ultrasonic hot embossing process

Ultrasonic Hot Embossing of polymers is one of the most attractive manufacturing methods of high-quality and complex microparts needed for biological and chemical processes. A little simulation work has been done to study the deformation mechanism and the required load in the Ultrasonic Hot Embossing of polymethyl methacrylate (PMMA). This paper developed a 2D coupled thermo-mechanical finite element model to simulate the forming behavior of the ultrasonic embossing process of PMMA, optimize the mold microfeature corner, and predict the embossing load as well. VDISP ABAQUS subroutine has been used to describe the downward motion of the mold assisted with ultrasonic vibration. The Arbitrary Eulerian-Lagrangian re-meshing technique has been implemented to refine the deformation zone during simulation to avoid divergence due to localized excessive deformation. Embossing load, temperature, stresses, strains, and energy dissipation have been recorded and analyzed. Simulation results revealed that the coupled thermo-mechanical FE Model efficiently captures the deformation behavior and Embossing load. It also proved that a Mold microfeature corner of 20 μm filet radius is recommended to adequately fill out the area around the mold and maintain uniform temperature and strain distributions.

Microstructure-dependent deformation mechanisms and fracture modes of gradient porous NiTi alloys

Gradient porous structures based on triply periodic minimal surfaces offer exceptional specific strength and multi-functionality. However, strain heterogeneity complicates their deformation mechanisms and fracture modes. In this study, we fabricated a series of gradient porous NiTi alloys based on gyroid (G), diamond (D), and I-WP (I) unit cells, with porosities ranging from 50% to 70%. Surprisingly, the I structure exhibited an abnormally high compressive strength of nearly 600 MPa at around 50% porosity, more than twice that of the G and D structures. This performance gap was attributed to the activation of mixed deformation mechanisms and distinct fracture modes. While the G structure showed a uniform radial strain distribution, the D and I structures displayed pronounced radial strain gradients with concentrated central strains. The D structure deformed through relative sliding of oblique struts, while the I structure maintained macrostructural stability, with thick edge struts providing continuous strain hardening until monolithic fracture. This unique deformation behavior results from the synergistic effects of its intrinsic macrostructural stability, significant radial strain gradients, and sufficiently thicker edge struts. The integration of metallurgical and architectural design principles represents a novel approach to tailoring the mechanical properties of gradient porous metals for advanced applications.

Study on the relationship between the microstructure characteristics, tensile properties and impact toughness of carbide-free bainitic steel

To understand the relationship between microstructure characteristics, tensile properties, and impact toughness of bainite structure, microstructure characterization, μ-DIC and mechanical tests were carried out on bainitic steel subjected to pre-quenching treatment, followed by austenitizing at 800 °C or 880 °C and then by austempering. The resulting microstructure after austempering is composed of bainite, retained austenite and intercritical ferrite and/or fresh martensite. Compared with 880 °C-austenitized specimen, the final microstructure in the 800 °C-austenitized specimen is significantly refined, and the amount of large martensite/austenite (M/A) islands is also decreased. The finer microstructure of the 800 °C-austenitized specimen results in a relatively uniform strain distribution during the tensile process, delaying the occurrence of tensile necking. In contrast, the strain of the 880 °C-austenitized specimen tends to concentrate at the interface between the bainite region and M/A islands, leading to premature fracture and decreased plasticity. In addition, the smaller retained austenite size in the 800 °C-austenitized specimen enhances its stability, leading to persistent work hardening behavior and improved plasticity. Furthermore, the decrease in the amount of M/A islands in the 800 °C-austenitized specimen reduces the initiation of cracks, and finer packets and blocks increase the proportion of high angle grain boundaries, enhancing the resistance to crack propagation. Therefore, the total absorbed energy and toughness of the 800 °C-austenitized specimen are about twice higher than those of the 880 °C-austenitized specimen.

3D Printed MXene-Based Wire Strain Sensors with Enhanced Sensitivity and Anisotropy.

Stretchable strain sensors play a crucial role in intelligent wearable systems, serving as the interface between humans and environment by translating mechanical strains into electrical signals. Traditional fiber strain sensors with intrinsic uniform axial strain distribution face challenges in achieving high sensitivity and anisotropy. Moreover, existing micro/nano-structure designs often compromise stretchability and durability. To address these challenges, a novel approach of using 3D printing to fabricate MXene-based flexible sensors with tunable micro and macrostructures. Poly(tetrafluoroethylene) (PTFE) as a pore-inducing agent is added into 3D printable inksto achieve controllable microstructural modifications. In addition to microstructure tuning, 3D printing is employedfor macrostructural design modifications, guided by finite element modeling (FEM) simulations. As a result, the 3D printed sensors exhibit heightened sensitivity and anisotropy, making them suitable for tracking static and dynamic displacement changes. The proposed approach presents an efficient and economically viable solution for standardized large-scale production of advanced wire strain sensors.

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.

Making titanium alloys ultrahigh strength and toughness synergy through deformation kinks-mediated hierarchical α-precipitation

Titanium alloys engineered in structural applications achieve ultrahigh strength primarily through precipitation strengthening of secondary α-phase (αs) during aging, while they often experience compromised ductility and toughness due to traditional strength-toughness tradeoff. In this study, we propose a novel strategy to address this conflict by introducing deformation kinks prior to conventional cold rolling (CR) and aging processes. These kinks are produced by cold forging (CF) to create macroscopic lamellar structures in β-grains, which alter strain partitioning during subsequent CR and ultimately tailor αs-precipitation upon aging. As a result, an ultrafine duplex (αe + β)-structure is formed within kink interiors, while hierarchical αs-precipitates are generated in the external β-matrix. This unique microstructure effectively enhances dislocation activity, promotes uniform plastic strain distribution and impedes crack propagation. Consequently, a simple Ti-V binary titanium alloy exhibits exceptional properties with ultrahigh strength ∼1636 MPa, decent ductility ∼5.4 % and appreciable fracture toughness ∼ 36.1 MPa m½. The synergetic properties surpass those obtained through traditional CR and aging processes for the alloy and even outperform numerous multielement engineering titanium alloys reported in literature. Our findings open up a new avenue for overcoming the strength-toughness tradeoff of ultrahigh-strength titanium alloys, and also offer a facile production route towards structural materials for advanced performance.