Search Results (432)

An ultra-high-strength press-hardening steel (PHS) and a high-strength dual-phase steel (DP) were butt-joined by the gas metal arc welding (GMAW) process, aiming to assess the effects of a high heat input welding process on the structure-property relationship and residual stress. The post-weld microstructure, the microhardness profile, the tensile behavior, and the experimentally obtained residual stresses (by x-ray diffraction) of the steels in dissimilar (PHS-DP) and similar (PHS-PHS, DP-DP) pair combinations have been analyzed. Results indicated that the ultimate tensile strength (UTS) of the dissimilar pair PHS-DP achieves a similar strength to the DP-DP joint, whereas the elongation was similar to that of the PHS-PHS weldment. The failure location of the tensile specimens was expected and systematically observed at the tempered and softer sub-critical heat-affected zone (SC-HAZ) in all welded conditions. Compressive residual stresses were consistently observed along the weldments in all specimens; the more accentuated negative RS were measured in the PHS joint attributed to the higher volume fraction of martensite; furthermore, the negative RS measured in the fusion zone (FZ) could be well correlated to weld restraint due to the sheet anchoring during the welding procedure, despite the presence of predominant ferrite and pearlite microstructures. Full article

The mechanics of an elastic sheet reinforced with fiber mesh is investigated when undergoing bilateral in-plane bending and stretching. The strain energy of FRC is formulated by accounting for the matrix strain energy contribution and the fiber network deformations of extension, flexure, and torsion, where the strain energy potential of the matrix material is characterized via the Mooney–Rivlin strain energy model and the fiber kinematics is computed via the first and second gradient of deformations. By applying the variational principle on the strain energy of FRC, the Euler–Lagrange equilibrium equations are derived and then solved numerically. The theoretical results highlight the matrix and meshwork deformations of FRC subjected to bilateral bending and stretching simultaneously, and it is found that the interaction between bilateral extension and bending manipulates the matrix and network deformation. It is theoretically observed that the transverse Lagrange strain peaks near the bilateral boundary while the longitudinal strain is intensified inside the FRC domain. The continuum model further demonstrates the bidirectional mesh network deformations in the case of plain woven, from which the extension and flexure kinematics of fiber units are illustrated to examine the effects of fiber unit deformations on the overall deformations of the fiber network. To reduce the observed matrix-network dislocation in the case of plain network reinforcement, the pantographic network reinforcement is investigated, suggesting that the bilateral stretch results in the reduced intersection angle at the mesh joints in the FRC domain. For validation of the continuum model, the obtained results are cross-examined with the existing experimental results depicting the failure mode of conventional fiber-reinforced composites to demonstrate the practical utility of the proposed model. Full article

Unlike previous studies focusing on two-layer structures or single-parameter effects, this work systematically investigates the influence of sheet layer combination modes on the mechanical properties of three-layer AA6063-T6 self-piercing riveting (SPR) joints through a combination of experimental testing and numerical simulation. Shear and cross-tensile tests were conducted on three-layer AA6063-T6 SPR joints with three distinct sheet layer combinations: T1 (top/middle: 100 × 40 mm², bottom: 40 × 40 mm²), T2 (top/bottom: 100 × 40 mm², middle: 40 × 40 mm²), and T3 (middle/bottom: 100 × 40 mm², top: 40 × 40 mm²). Experimental results reveal significant differences in joint strength and failure modes across the three combinations. T3 joints exhibited the highest shear strength (9.16 kN) but the lowest cross-tensile strength (3.56 kN), whereas T1 joints showed the highest cross-tensile strength (4.97 kN) but moderate shear strength (8.76 kN). A high-fidelity finite element model was developed to simulate the SPR joint under varying sheet layer combinations, incorporating precise geometric details (0.25 mm mesh at critical zones) and advanced contact algorithms (friction coefficient μ = 0.2). Numerical simulations revealed the stress distribution and failure mechanisms under shear and cross-tensile loading, aligning well with experimental observations. Analysis highlights that the mechanical performance of the joint is governed by two key factors: (1) the stress redistribution in sheet layers due to combination mode variations, and (2) the interlocking strength between the rivet and sheets. These findings provide practical guidelines for optimizing sheet layer combinations in lightweight automotive structures subjected to mixed loading conditions. Full article

Jointing is inevitable for CFRTP (carbon fiber reinforced thermoplastic) component applications in the automotive industry. In this study, commonly used jointing methods were applied to fasten CFRTP components. Three types of jointing methods. Ultrasonic welding, bolted joints, and adhesive joining, and three types of CFRTP materials, conventional cross-ply, ultra-thin prepreg cross-ply, and sheet molding compounds, were selected. The influence of the jointing methods on mechanical properties and damage patterns under bending load has been investigated. The finite element models were developed to predict the hazardous area and structural stiffness of jointed structures; the simulation results showed good agreement with experimental ones. The results indicate that the ultrasonic welding could reach similar bending stiffness compared to adhesive joining, whereas the stiffness of bolt jointed structures is relatively lower due to the contact separation induced by the bending deformation. Overall, the finite element model results correlated well with the experimental data. Full article

This study investigates the effect of welding speed on the microstructure and mechanical properties of pulsed laser lap-welded 0.2 mm 316L stainless steel sheets, commonly used in fuel cell bipolar plates. Welding speeds ranging from 6 to 26 mm/s were tested while other laser parameters remained constant. Results show that increasing welding speed reduces heat input, overlap factor, and weld dimensions. A transition from full to partial penetration occurs beyond 6 mm/s, with no visible heat-affected zone. The weld microstructure features columnar ferrite near fusion boundaries and globular ferrite in the center. Tensile–shear tests reveal that welds maintain higher strength than the base metal up to 22 mm/s, with all fractures occurring in the base material. An optimal speed range of 10–14 mm/s ensures defect-free joints with improved mechanical performance. These findings provide practical guidance for thin-gauge stainless steel welding in fuel cell applications. Full article

A new brazing process for thin-walled stainless steel was proposed by combining green and efficient Ni-Cr-P electrodeposition with brazing technology. Novel information was attained by analyzing the electrodeposited Ni-Cr-P interlayers and the brazed joints and characterizing them using a combination of advanced techniques. The incorporation mechanisms of impurities (i.e., oxygen and carbon) in the Ni-Cr-P interlayers electrodeposited from a Cr(III)–glycine solution were revealed. The oxygen mainly came from the Cr(III)–hydroxy complexes formed by the hydrolysis and olation between Cr(III) complexes and OH⁻ ions near the cathode. Glycine did not directly participate in the cathode reactions but decomposed on the anode surface. These byproducts (carbonyl compounds) were directly incorporated into the interlayers in a molecular pattern, forming a weak link to the metallic chromium. Brazing test results showed that a certain amount of Cr₂O₃ powder, formed by the decomposition of chromium hydroxides in the interlayers under high-temperature catalysis, would cause the degradation of the brazed joints. Using the step-wise brazing method, the brazing sheets were first annealed to eliminate the impurities by utilizing the strong reducing effect of hydrogen and the weak link characteristics between carbonyl compounds and metallic chromium atoms. An excellent joint with a shear strength of 63.0 MPa was obtained by subsequent brazing. The microstructural analysis showed that the brazed seam was mainly composed of a Ni-Fe-Cr solid solution, the Ni₃P eutectic phase, and small quantities of the Ni₅P₂ phase scattered in the Ni₃P eutectic phase. Fracture mode observations showed that the cracks extended along the interface between the brittle P-containing phase and the primary phase, resulting in fracture. Full article

To address solder paste drawbacks, such as die contamination and flux residue, a polymer-based sheet containing Sn-3.0 (wt%) Ag-0.5Cu solder particles as fillers was fabricated, and its bonding characteristics were analyzed. The reductant in the manufactured sheet evaporated while removing the oxide layers on the solder and copper finish surfaces during heating. Subsequently, the resin component (polymethyl methacrylate) began to decompose thermally and gradually dissipated. Ultimately, the resulting joint formed a solder interconnection with a small amount of residual resin. This joint is expected to exhibit superior thermal conductivity compared with composite joints with a polymer matrix structure. Die-attach tests were conducted in air using the fabricated sheet between Cu finishes. Results showed that joints formed at 300 °C for 30 s and 350 °C for 10 s provided excellent shear strength values of 48.0 and 44.3 MPa, respectively, along with appropriately developed intermetallic compound (IMC) layers at the bonding interface. In contrast, bonding at 350 °C for 60 s resulted in excessive growth of IMC layers at the interface. When comparing size effects of solder particles, type 6 particles exhibited superior shear strength along with a relatively thinner total IMC layer thickness compared to when type 7 particles were used. Full article

Bamboo is a green, renewable material with high strength and low cost, but raw bamboo has limited application in residential buildings due to its irregular shape and dry cracking. In this regard, this work proposed a novel ecological sandwich panel to explore the potential combination of engineered bamboo and raw bamboo culms. Face sheets made of glued laminated bamboo panels were bonded to the bamboo culm core via epoxy resin and mortise–tenon joints. Two groups of specimens with height-to-thickness ratios of 4.63 and 5.37 were tested through edgewise compression to investigate the failure modes, strength and rigidity. The results revealed that the specimens had no overall stability problem under axial loading, but exhibited delamination and local bulging to the face sheets. When the height-to-thickness ratio increased from 4.63 to 5.37, but still belonged to the short member range, the area of the adhesive interface increased by 16.13%, and the edgewise compressive strength and rigidity increased by 17.57% and 35.04%, respectively. This indicated that the capacity and rigidity were mainly determined by the connection strength, which was obviously affected by the manufacturing and assembly errors. Accordingly, increasing the connection strength could be helpful for improving the load-carrying capacity and ductility of such panels. Full article

This study investigated the impact of zinc oxide’s (ZnO’s) morphology on the piezoelectric performance of polyvinylidene fluoride (PVDF) composites for flexible sensors. Rod-like (NR) and sheet-like (NS) ZnO nanoparticles were synthesized via hydrothermal methods and incorporated into PVDF through direct ink writing (DIW). The structural analyses confirmed the successful formation of wurtzite ZnO and enhanced β-phase content in the PVDF/ZnO composites. At a degree of 15 wt% loading, the ZnO-NS nanoparticles achieved the highest β-phase fraction (81.3%) in PVDF due to their high specific surface area, facilitating dipole alignment and strain-induced crystallization. The optimized PVDF/ZnO-NS-15 sensor demonstrated superior piezoelectric outputs (4.75 V, 140 mV/N sensitivity) under a 27 N force, outperforming its ZnO-NR counterparts (3.84 V, 100 mV/N). The cyclic tests revealed exceptional durability (<5% signal attenuation after 1000 impacts) and a rapid response (<100 ms). The application trials validated their real-time motion-monitoring capabilities, including finger joint flexion detection. This work highlights the morphology-dependent interfacial polarization as a critical factor for high-performance flexible sensors, offering a scalable DIW-based strategy for wearable electronics. Full article

This paper explores a novel double-flush riveting process for assembling hybrid busbars made from aluminum and copper sheets. The process involves drilling and forging countersunk holes with controlled geometry in both materials followed by compression of cylindrical rivets into the holes to create strong, form- and force-closed mechanical joints. Experimental and numerical analyses are combined to examine material flow, quantify the required forces, and assess the structural integrity of the joints through destructive testing. Additionally, the electrical resistance of these novel joints is evaluated and compared with that of ideal and conventional fastened hybrid busbar joints in order to assess their performance and reliability in real-world electrical service conditions. The results indicate that the novel double-flush riveting process is a viable alternative to other conventional joining processes, such as fastening, delivering good structural integrity and enhanced electrical conductivity for hybrid busbar applications. Full article

Flexible wearable strain sensors demonstrate promising application prospects in health monitoring, human-machine interaction, motion tracking, and the detection of human physiological signals. Although laser-induced graphene (LIG) materials have been extensively utilized in these scenarios, traditional types of LIG sensors are constrained by intrinsic limitations, including discontinuous conductive networks and electromechanical responsive hysteresis. These limitations hinder their applications in micro-strain detection scenarios. Consequently, enhancing the performance of LIG-based sensors has become a crucial priority. To address this challenge, we developed a novel MXene/LIG composite featuring optimized conductive networks and interfacial coupling effects through the systematic enhancement of LIG. The flexible strain sensor fabricated using this composite exhibits exceptional performance, including an ultra-low sheet resistance of 14.1 Ω, a high sensitivity of 20.7, a micro-strain detection limit of 0.05%, and a rapid response time of approximately 65 ms. These improvements significantly enhance electromechanical responsiveness and strain detection sensitivity. Furthermore, the sensor exhibits remarkable stability under varying tensile strains, particularly showing outstanding repeatability across 2500 cyclic tests. Notably, when applied to the pilot health monitoring scenarios, the MXene/LIG-based sensor demonstrates robust capability in detecting body movement signals such as micro-expressions and joint movements. This establishes a novel and highly effective technological solution for the real-time monitoring of pilots’ motion states during operational scenarios. Full article

A new class of Gaussian random fields is introduced in this article, described as additive Brownian sheets (ABSs), which can be regarded as a type of generalized Brownian sheet encompassing Brownian motions, Brownian sheets, and additive Brownian motions. The existence, joint continuity and the Hölder law of the local times for ABSs are derived under certain conditions, and some results of the intersection local times for two independent Brownian sheets are also given as special cases. Furthermore, the intersection local times for two independent Brownian sheets in a Hida distribution is proved through white noise analysis, and the Wiener chaos expansion of the intersection local times is expressed in terms of S-transform. Additionally, the large deviations for the intersection local time of two independent Brownian sheets are established. The multi-parameter Gaussian random fields have become a core tool for complex system analysis due to their flexible multidimensional modeling capabilities. With the improvement of computational efficiency and interdisciplinary integration, the ABS constructed in this article will unleash greater potential in fields such as metaverse simulation, financial mathematics, climate science, precision medicine, quantum physics, and string theory. Full article

Forming hybrid structures into complex shapes is key to address lightweighting of automotive parts. Recently, an innovative joining technique between aluminium and Carbon Fibre-Reinforced Polymer (CFRP) based on mechanical interlocking through sheet punching has been developed. However, scaling up the solution requires the assessment of challenges, such as multi-material forming and joint integrity, after forming operations. Therefore, this work proves the feasibility of forming aluminium–CFRP prepreg panels into complex omega-shaped profiles following a conventional cold-stamping process. Forming without defects was possible even in specimens featuring mechanical joints generated through punching. The effect of the CFRP position (in the inner or the outer side of the formed profile), the number of mechanical joints, the addition of a Glass Fibre-Reinforced Polymer (GFRP) intermediate layer to prevent galvanic corrosion and adequate lubrication on necking, cracking, springback behaviour and the final geometry after curing were studied. Compression tests were performed to assess the mechanical response of the hybrid profile, and the results showed that the addition of CFRP in the aluminium omega profile changed the buckling behaviour from global bending to axial folding, increasing the maximum compression load. Additionally, the presence of mechanical interlocking joints further improved the mechanical performance and led to a more controlled failure due to buckling localization in the geometric discontinuity. Full article

The article presents the results of experimental studies on the symmetrical and asymmetrical rolling process of composite laminate sheets consisting of difficult-to-deform Ti and Ni materials. Composite sheets joined by explosive welding were used for the tests. The aim of the research was to determine the impact of plastic shaping conditions in the rolling process on the quality and selected functional properties of the materials constituting the layered composite. The rolling process was carried out cold on a duo laboratory rolling mill with a roll diameter of 300 mm. During the rolling process, the influence of the rolling process conditions on the distribution of metal pressure forces on the rolls was determined, as well as the shear strength and microstructural studies of the joint area of the layered composites. As part of the conducted considerations, residual stress tests were carried out using the Barkhausen noise method. The scientific aim of the presented work was to determine the optimal conditions for the plastic processing of multi-layer Ti-Ni sheets. The results presented in the work allowed for determining the most favorable conditions for the rolling process. Full article

This study explores the friction stir welding (FSW) of thin aluminum sheets, focusing on alloys 1050 and 5754. FSW, a solid-state joining technique, offers advantages like minimal deformation and high joint strength, but optimizing welding parameters is crucial for sound welds. In order to investigate the optimum welding parameters, the Taguchi method was employed, in which key parameters such as rotational and welding speed were optimized to enhance tensile strength and weld quality. The tensile testing of the welded specimens revealed that the optimal combination—1000 RPM rotational speed and 250 mm/min welding speed—produced the highest tensile strength and weld quality. The results highlight the importance of parameter optimization in ensuring strong, stable welds, with rotational speed having the most significant influence. Additionally, excessive rotational speeds were found to weaken welds due to excessive heat input, while a slower welding speed contributed to greater weld stability. Full article