Search Results (1,259)

Fused silica–aluminum alloy dissimilar connections are in urgent demand in fields such as aerospace optoelectronic packaging, vacuum optical windows, and micro-electro-mechanical systems, yet the dramatic mismatch in thermal-expansion coefficient and thermophysical properties between the two materials has long been a bottleneck for reliable joining. Current ultrafast laser welding of such heterogeneous systems still suffers from prominent problems, including stringent optical contact requirements, high crack sensitivity on the fused silica side, and unclear coupling mechanism between clamping conditions and joint defects. This work systematically studies the joining process of femtosecond laser welding of fused silica and 6061 aluminum alloy dissimilar materials, focusing on the effects of scanning speed, pulse energy, scanning spacing, and fixture preload on the shear strength, microstructure, and elemental diffusion behavior of the joints. The results confirm that scanning speed and scanning spacing have a synergistic effect on heat input density; the magnitude of the fixture preload is a key factor determining the interfacial residual stress and crack sensitivity. By optimizing the scanning speed (6 mm/s) and combining it with a low preload and 140 μm scanning spacing, a high-strength heterogeneous joint with uniform elemental transition and no macroscopic cracks can be obtained. This study provides a detailed process-optimization approach for high-quality laser welding of dissimilar brittle/ductile materials. Full article

In this work, conventional friction stir lap welding (FSLW), self-riveting FSLW (R-FSLW) and ultrasonic-assisted R-FSLW (UR-FSLW) were employed to join dissimilar AA6061 and AZ31 alloys. The relatively thick Al-Mg intermetallic compound (IMC) layer provided limited metallurgical bonding, causing the FSLW joint to fail in a brittle manner at a low tensile shear force of 875 N. The self-riveting introduced additional mechanical interlocking: the R-FSLW joint, featuring AA6061 rivets, exhibited a 22% increase in tensile shear force compared with the FSLW joint. Nevertheless, cracks formed along the thick Al-Mg IMC layer around the AA6061 rivets, which retained the brittle fracture characteristic. In contrast, ultrasonic assistance not only improved the rivet filling rate (reducing the unfilled area from 0.83 mm² to 0.61 mm²) but also suppressed Al-Mg IMC layer growth and eliminated cracks. Moreover, ultrasonic assistance increased the stored energy and promoted material flow, refining the grains in the nugget zone (NZ) and thereby raising the average hardness of NZ. Consequently, with AA6061 rivets and refined microstructures, the UR-FSLW joint delivered a tensile shear force of 1280 N and an elongation double that of the FSLW joint, accompanied by a fracture mode transition from brittle to ductile-brittle. Full article

Engineering components often require different properties in different regions, and a single material may not provide all of them. Reliable joining is important for refractory metal–steel, dissimilar superalloy, and Ti/Mg combinations. Field-assisted sintering technology/spark plasma sintering (FAST/SPS) combines pressure with rapid heating for direct joining and fabrication of interlayered and graded metallic structures in short cycles. This review evaluates factors affecting bond formation and mechanical integrity at FAST/SPS-processed metallic interfaces. Sufficient real contact is needed for load transfer but does not alone ensure mechanical integrity. Surface oxides can restrict contact, while local deformation may increase contact area and disrupt oxide films. As contact develops, atomic transport and interfacial reactions may alter transition-region composition and phase morphology, affecting fracture paths. Interlayers may improve contact and limit undesirable reactions but can also create new interfaces and reaction regions. Compositional transitions, reaction regions, and local hardness indicate interface development, but assessing their mechanical significance requires mechanical testing and fracture analysis. Room-temperature performance alone does not define service behavior. Thermal cycling, high heat flux, electrical conditions, or corrosive environments may therefore require application-specific evaluation. Differences in materials, equipment, geometry, and test methods limit direct comparison. Processing windows should therefore be tailored to each material pair and interface architecture according to operating temperature, loading, functional requirements, and environmental exposure. Full article

Nomex honeycomb core sandwich composites are attractive for lightweight structural applications because of their high specific stiffness. However, drilling required for mechanical joining can introduce both surface and subsurface damage and may change the mechanical and dynamic response of the structure. This study examines Nomex aramid honeycomb sandwich composites with C/C/C, C/G/C, G/C/G, and G/G/G face-sheet configurations using three-point bending, drilling, image analysis, ultrasonic C-scan, and acoustic impact measurements. The C/C/C configuration reached an average bending load 36.05% higher than G/G/G and reduced the entry and exit side delamination areas by 88.91% and 78.89%, respectively. Although C/C/C produced the highest thrust forces during drilling, it also showed the smallest surface and internal damage regions, indicating that thrust force alone does not fully describe hole quality. C/G/C also exhibited less damage than G/C/G; however, these two hybrid configurations differ in both carbon/glass content and ply position, so the contribution of each factor cannot be separated independently. After drilling, the natural frequency decreased, and the damping ratio increased in all configurations. Overall, the carbon-rich face sheets provided higher bending resistance and more effectively limited drilling-induced damage. Full article

Joining dissimilar lightweight metals, such as magnesium (Mg) and titanium (Ti), presents critical challenges due to their differing physical properties and limited mutual solubility. This research explores the potential of laser impact welding (LIW) to overcome these barriers by investigating the effects of aluminum (Al) content in Mg-Al alloys, interlayer integration, and the formation of intermetallic phases at the bond interface. Emphasis is placed on understanding how variations in Al composition and the inclusion of an Al interlayer influence the bonding mechanisms between Mg and Ti. Through detailed microstructural analysis and phase identification, this study characterizes the intermetallic phases present at the weld interface, examining their size, distribution, and location. The presence of an Al interlayer was found to significantly improve bonding success, promoting favorable interface morphology and minimizing detrimental intermetallic formation. These findings provide key insights into the underlying mechanisms enabling successful LIW of dissimilar lightweight metals and offer valuable guidance for industrial applications seeking to advance joining strategies in high-performance alloy systems. Full article

Friction stir welding (FSW) is a solid-state joining process widely used for aluminum alloys due to its low heat input, reduced distortion, and ability to produce high-quality joints. However, excessive tool forces generated during the welding process can increase machine loading, accelerate tool wear, and negatively affect the process efficiency. Therefore, understanding the relationship between welding parameters, tool forces, and the joint performance is essential for achieving high-quality welds while avoiding unnecessary mechanical loads. In this study, 4 mm thick AA5754 aluminum alloy plates were joined using the FSW process, and the feasibility of using tool force measurements for process optimization was investigated. A comprehensive experimental matrix consisting of nine different rotational speeds and ten different tool travel speeds was established based on preliminary studies and previous literature. During each welding operation, forces acting on the tool in the F_x, F_y, and F_z directions were continuously recorded. The welded joints were evaluated through tensile testing (Zwick Z300 universal testing machine, ZwickRoell, Ulm, Germany), hardness measurements, and microstructural characterization using scanning electron microscopy (SEM) (ZEISS Merlin scanning electron microscope, Carl Zeiss Microscopy GmbH, Oberkochen, Jena, and Göttingen, Germany). A Pearson correlation analysis and a two-way analysis of variance (ANOVA) were performed at a 95% confidence level to quantify the relationships and statistical significance of the process parameters. The results showed that F_z was the dominant force component during welding. The rotational speed had a statistically significant effect on the tensile strength, yield strength and hardness (p < 0.05), accounting for 99.39% of the total variation in hardness. For the mean tool force, both the rotational speed and the tool travel speed were statistically significant (p < 0.0001), contributing 38.48% and 47.16% of the total variation, respectively. The rotational speed also accounted for 81.55% of the variation in the maximum axial force. The Pearson correlation analysis showed a strong negative correlation between the rotational speed and hardness (r = −0.73), whereas the tool travel speed showed positive correlations with F_x (r = 0.61), F_z (r = 0.62), and the mean tool force (r = 0.68). Despite the increased tool loading associated with higher travel speeds, no corresponding improvement in the mechanical performance was observed. The results demonstrated that appropriately selected welding conditions produced joints with a yield strength and hardness exceeding 90% of the corresponding base material properties while maintaining relatively lower tool forces. SEM observations confirmed grain refinement in the stir zone. Overall, the combined correlation and ANOVA results demonstrate that real-time tool force monitoring can provide a quantitative basis for selecting FSW parameters that achieve an adequate mechanical performance while minimizing unnecessary machine and tool loading. Full article

This work sets out a complete systems engineering approach to lessen the world’s plastic waste problem—as nearly 91% of original plastic waste is not recycled. The study deals with the financial difficulties of made-to-order production by offering a local production scheme using Distributed Recycling by way of Additive Manufacturing—DRAM. A unique mechanical recycling process was developed, at the heart of which is a straight “bottle-to-strip” supply method. This new idea allows post-use PET waste to become custom figures by not using the energy-heavy filament-pushing step. The technical build joins a three-level e-trade stage with a changed Fused Deposition Modeling—FDM—making line. Findings from tests show the put-in-place system lowers the changeable cost of 3D print material from about $20 a kilo for new stuff to $1–2 a kilo for recycled PET strips. Full article

Metaheuristics require sustained global search without sacrificing local refinement, yet many variable-structure methods change operators through one-way iteration schedules. We introduce the Weather State Ants Optimizer (WSAO), in which a discrete-time Markov chain recurrently selects one of three population updates. Sunny, cloudy, and rainy states correspond to global exploration, movement toward nests, and local refinement, respectively. An archive-based mechanism also maintains several spatially separated nests as concurrent search centers. Thirty independent runs compared WSAO with 11 algorithms on 29 CEC2017 and 12 CEC2022 functions. WSAO achieved the lowest Friedman mean rank on both suites, at 2.48 and 2.33. Across five constrained design cases, it joined the leading group by mean objective value on four cases and ranked second on pressure-vessel design. Targeted CEC2022 controls showed that no alternative transition matrix dominated the baseline. Eliminating the trial perturbation worsened every selected function, whereas the contribution of multiple nests depended on the landscape structure. The combined evidence supports recurrent state-controlled search as a competitive framework for continuous numerical and constrained optimization. Full article

Perforation damage can significantly reduce the load-carrying capacity of aluminum alloy plates. Adhesive–rivet hybrid repair combines the continuous load-transfer capability of adhesive bonding with the reliable mechanical connection provided by riveting; however, quantitative methods for matching damage size, rivet parameters, and adhesive load-carrying capacity remain insufficient. In this study, perforated 2A12-T4 aluminum alloy plates were investigated. Based on the equal-strength criterion and load-transfer equilibrium, a strength-matching relationship between the adhesive layer and blind rivets was established, and a residual-strength assessment method for the repaired structure was proposed. Two typical two-part epoxy adhesives with different shear strengths, Araldite-2015 and Lord 320/322, which have application backgrounds in aerospace structural joining and repair, were selected. Combined with blind rivets of different load-carrying capacities, they formed strong-adhesive/weak-rivet and weak-adhesive/strong-rivet configurations to investigate the mechanical response under different adhesive–rivet strength-matching conditions. Quasi-static tensile tests, digital image correlation (DIC) measurements, and finite element analyses incorporating a cohesive zone model and a ductile damage criterion were performed to investigate load distribution and failure behavior. The results show that the maximum deviation between the finite element predictions and the experimental failure loads is 5.02%. Before significant adhesive failure, the adhesive layer carries up to 67.25% of the transferred load, indicating a substantial load-sharing effect on the rivets. The hybrid-repaired structures mainly fail along the cross-section through the outermost rivet holes. The proposed residual-strength model shows agreement with the investigated experimental dataset, with a maximum deviation of 6.37%; because the reduction coefficient contains an empirical calibration component, broader predictive applicability requires independent validation. For the six repair configurations, the strength recovery ratios all exceed 74%, the maximum strengthening ratio reaches 55.49%, and the maximum value of the newly proposed repair ratio is 0.48 kN/g. Unlike previous studies that mainly focused on comparisons of joining methods, failure behavior, or individual process parameters, this study establishes a quantitative framework that links damage size and material load-carrying capacity with adhesive–rivet parameter matching and post-repair residual-strength assessment. The proposed method provides theoretical and experimental support for the design and strength evaluation of adhesive–rivet hybrid repairs for perforated aluminum alloy thin plates under fully cured conditions. Full article

To meet the demands for lightweight design and high-conductivity connections in new energy vehicles, the high-quality joining of dissimilar Al/Cu metals has emerged as a critical research focus. In this study, laser welding was performed on 2 mm-thick 1060 pure aluminum and T2 copper plates. The effects of laser power (3.6–4.0 kW) and welding speed (0.9–1.5 m/min) on the interfacial microstructural evolution and mechanical properties of the lap joints were systematically investigated. The results demonstrate that the macroscopic morphology of the weld is primarily governed by heat input: excessive laser power induces transverse cracking, whereas an overly low welding speed promotes porosity. Microstructural analysis revealed that intermetallic compounds (IMCs), such as Al₂Cu, AlCu, and Al₄Cu₉, predominantly form at the interface, with their morphology and distribution varying significantly depending on the heat input. Under the optimized parameters of a 3.8 kW laser power and a 1.2 m/min welding speed, sufficient mixing of the molten Al and Cu was achieved. This promoted the formation of fine, dispersed IMCs accompanied by a continuous Al–Cu eutectic layer at the interface, yielding a maximum tensile-shear load of 1561 N. This research elucidates the intrinsic relationship between heat input and the microstructure–property correlation of Al/Cu laser-welded joints, identifying a viable process window for 2 mm-thick sheets and providing theoretical and practical guidance for joining dissimilar medium-thickness metal plates. Full article

Transition joints between lightweight aluminum alloys and high-strength steel are widely employed in the transportation industry, and especially in shipbuilding, as intermediate inserts between structural components made of dissimilar metals. While traditional fusion welding presents considerable difficulties in joining such metals, explosive welding is particularly suitable for producing thick plates with large contact surfaces between aluminum and steel. The process setup and the various parameters involved have been described in several articles, as also documented by some recent overviews. However, there has been no review of the most recent papers specifically dealing with the metallurgical characteristics of these interfaces, as well as with their mechanical properties. Thus, the present article aims to fill this gap by outlining a review on the state of the art to correlate the process parameter setting, interface characteristics, and weldability of aluminum/steel transition joints, and then focusing on the most relevant studies concerning the mechanical behavior under static and fatigue conditions of trimetallic joints (Al alloy/commercially pure Al/structural steel) for shipbuilding applications. The effects of welding-induced thermal fields during structural joint insertion are also taken into account, and the most recent proposals for strategies to improve mechanical performance are examined. Full article

Battery packs for new energy vehicles have evolved from simple load-bearing and protective assemblies into multifunctional safety structures integrating structural support, crash protection, thermal-runaway mitigation, flame retardancy, electrical insulation, electromagnetic interference shielding, waterproof sealing, and long-term reliability. Fiber-reinforced polymer composites are promising for upper covers, underbody shields, trays, cross beams, side frames, and local protective structures because of their low density, corrosion resistance, design flexibility, and functional-integration potential. However, composite-part performance is strongly governed by forming. Resin flow, impregnation, curing or cooling shrinkage, fiber orientation, filler dispersion, and interfacial bonding may induce voids, dry spots, resin-rich regions, delamination, warpage, and fiber waviness, thereby affecting load bearing, sealing, thermal protection, and durability. This review focuses on composite-forming technologies for new energy-vehicle battery packs. It summarizes component-level service requirements and material systems and compares representative forming routes, including sheet molding compound (SMC), prepreg compression molding/wet compression molding (PCM/WCM), resin transfer molding/high-pressure resin transfer molding (RTM/HP-RTM), vacuum-assisted resin transfer molding (VARTM), long-fiber thermoplastic direct processing (LFT-D), glass-mat thermoplastic (GMT), thermoplastic sheet forming, pultrusion, and multi-material joining. These routes are evaluated from six dimensions: material form, forming cycle, typical defects, representative mechanical performance, applicable components, and engineering maturity. The review further discusses defect mechanisms, performance effects, detection and control methods, and the roles of in-line monitoring, non-destructive testing, process simulation, machine learning, and digital twins in closed-loop quality manufacturing. Finally, engineering challenges are examined in multi-material joining, thermal-safety integration, low-carbon recycling, and standard certification. Composite-material battery-pack structures should therefore be developed as coordinated design and closed-loop manufacturing systems linking materials, processes, defects, performance, and validation. Full article

The aluminum/steel hybrid body structure represents one of the key breakthrough directions for automotive lightweighting. However, aluminum and steel differ significantly in their thermophysical properties, making it difficult to achieve high-quality joining between them using conventional fusion welding methods. To address this challenge, the present study employs ultrasonic welding technology to achieve spot welding in a steel/aluminum/steel three-layer plate configuration. The experimental welding of the three-layer sheets and interfacial phase identification were first carried out, followed by the development of an ultrasonic vibration–thermal–mechanical coupled numerical simulation model, the accuracy of which was verified through experiments. On this basis, the dynamic evolution of the temperature and stress fields during the ultrasonic welding process was systematically revealed. Furthermore, this novel engineering simulation case was introduced into the teaching of the course Engineering Finite Element and Numerical Computation yielding favorable educational outcomes. Full article

The continuous joining of aluminum alloys to engineering thermoplastics has emerged as a promising manufacturing path for lightweight hybrid structures, yet the influence of polymers’ mechanical behavior on friction stir joining remains poorly understood. This work investigates the role of melt rheology on the morphology, joining interface, and mechanical strength of dissimilar joints that combine AA6082-T6 with two engineering-grade thermoplastics, Noryl^® GFN2 and SustaPEEK^®. Two joining strategies were assessed under identical processing conditions: conventional friction stir joining (FSJ) and through-slot friction stir joining (TS-FSJ), the latter incorporating thin titanium strips intended to reduce heat transfer to the polymer. Joint morphology was assessed by optical and scanning electron microscopy, mechanical performance was evaluated through quasi-static tensile-shear testing, and the rheological behavior of both polymers was characterized by steady shear and oscillatory measurements. Conventional FSJ produced defect-free aluminum–Noryl joints, with a mechanical strength of 111.3 ± 8.4 kN/m, whereas aluminum–PEEK joints exhibited localized polymer overflow, poor surface finish and scattered strength performance of 116.7 ± 77.2 kN/m. Rheological measurements showed that PEEK exhibited higher melt viscosity and viscoelastic moduli, restricting polymer flow and promoting unstable interface formation. Although titanium inserts reduced heat transfer in TS-FSJ, their deformation reduced the effective joining area, resulting in lower tensile strength. Polymer rheology was identified as one of the key factors governing material flow, defect formation, process stability, and the joints’ mechanical performance, emphasizing the importance of tailoring the processing parameters reflecting the rheological characteristics of each polymeric base material. Full article

Battery-powered mobile robots that rely on an edge server for perception spend energy in three places at once: the on-board processor, the radio front end and the drivetrain. These budgets are normally optimised separately, which is a mistake, as lowering the processor clock pushes work onto the wireless link, transmitting into a poor channel costs far more than waiting for a better one, and where the robot drives determines what the channel will be. We formulate the co-management of all three as a minimisation of long-run average energy for a fleet sharing an access point and subject to task deadlines, a power budget and a mission-progress constraint that forces every policy under comparison to cover the same ground. The resulting stochastic mixed-integer non-convex program is made tractable by a Lyapunov drift-plus-penalty argument that decomposes it into four per-slot subproblems: a square-root clock rule, a water-filling transmit-power rule with an explicit on/off test, a join-the-shorter-queue offloading split, and a short lookahead over admissible speeds. The policy needs no channel or workload statistics and attains an A per-task deadline mechanism, feasibility floors on the clock and transmit decisions, and closes the gap between queue-stability guarantees and individual task deadlines, which drift arguments alone do not bound. The policy needs no channel or workload statistics and attains an $\left[O\right(1/V),O(V\left)\right]$ energy–delay tradeoff, stated under precisely qualified assumptions. In a per-task simulation study against six baselines, the policy reduced combined communication and computation power by 25% relative to the strongest deadline-compliant baseline ($p<{10}^{-4}$) at equal mission progress, and was the only scheme to hold deadline violations below 0.5% across the full load range, where every baseline exceeded 16% at high load. Full article