Lap Shear Tests Research Articles

A sprayable and rapidly cross-linked hydrogel membrane for fruit preservation

Hydrogel membranes (HMs) exhibit great potential for fruit preservation due to their excellent biocompatibility and scalability. However, most HMs cannot meet the requirements of rapid and large-scale preparation. In this work, one type of hydrogel paint that can form a uniform membrane on fruit surfaces by either spraying, brushing, or dipping methods has been developed. The hydrogel paint, which utilizes ethanol to dynamically modulate the hydrogen-bond cross-linking between tannic acid (TA) and polyvinyl alcohol (PVA), enables the rapid and uniform formation of a membrane (PVA@TA1 HM) on fruit surfaces within 50 s by ethanol evaporation. The PVA@TA1 HMs can not only effectively extend the freshness of fruits to 8 days (25 °C, 40 % relative humidity) but also possess properties such as easy cleaning, recyclability, and antioxidation. Besides, the natural antibacterial properties of TA endow the PVA@TA1 HMs with long and effective antibacterial activity (antibacterial rate ≥ 99.7 %, lasting for 7 days) against both Staphylococcus aureus and Escherichia coli. Furthermore, the dense hydrogen-bonds cross-linking between PVA and TA molecules endow the PVA@TA1 HMs with high tensile strength (≥ 7 MPa) and significantly reduces their water and oxygen transmission rate. Moreover, the adhesion of hydrogel paint has been significantly improved with the introduction of TA, as validated by both atomic force microscopy and lap-shear adhesion tests, at both micro- and macro- scales. This work provides a method for the rapid and large-scale preparation of HMs under different working environments, which shows great potential for fruit preservation.

Cavity self-healing mechanism at the interface of high-Cr ferritic steel/austenitic steel dissimilar diffusion-bonded joint during cyclic phase transformation treatment

In this work, cyclic phase transformation treatment (CPTT) was developed to achieve self-healing of interfacial voids in high-Cr ferritic steel/austenitic steel dissimilar diffusion-bonded joints. The evolution of voids was analyzed based on microstructural characteristics, and mechanical properties of joints were assessed through lap-shear tensile tests. The results indicate that, in contrast to isothermal heat treatment (IHT), CPTT significantly enhances efficiency of cavity healing, leading to substantial improvements in both interface bonded ratio and shear performance of joints. By considering equivalent interfacial internal stress, a kinetic model for cavity healing was proposed, incorporating coupled the interface and surface diffusion, and the power-law creep mechanism. Simulation results demonstrate that diffusion predominates during cavity healing with negligible contribution of plastic flow. The actual cavity healing can be divided into two stages: in initial stage the large penny-shaped cavities become shorter in length with negligible change of height, while in the final stage, nearly circular voids shrinkage with a significant decrease of void size due to the enhanced effect of local surface diffusion. Moreover, it suggests that tensile internal stresses can impede healing or even promote residual void growth. Conversely, normal compressive internal stresses within cavity healing zone induced by the cyclic α↔γ phase transformation during CPTT intensify chemical gradients around void neck. This promotes accelerated atomic diffusion adjacent to void neck region, thereby resulting in a notable reduction in the duration required for complete cavity healing.

Study on Effects of Pulsed Current Treatment on Ultrasonic Welded Joint of Al5052‐H32 Alloy

The effect of pulse current on the mechanical properties of ultrasonic welded joints of 5052‐H32 aluminum alloy (Al5052‐H32) plate with a thickness of 2 mm is investigated experimentally. First, ultrasonic lap welding is performed to prepare the welded joint. Then, the pulsed current with different current densities and durations is applied to the welded joint. The impact of pulsed current on the properties of the welded joints is evaluated through tensile lap shear testing, observation using a metallographic microscope, and hardness testing. In the results, it is indicated that the tensile lap shear strength, elongation, and hardness of the welded joints can be improved by applying pulsed current properly. However, excessive input of electrical energy can lead to a decrease in the mechanical properties of the welded joints. Compared to the joint without pulse current treatment, the microstructure shows significant healing of the weld seam under the action of pulsed current. The feasibility of enhancing the mechanical performance of ultrasonically welded joints through the utilization of pulsed current is highlighted by these findings.

Polyurethanes Made with Blends of Polycarbonates with Different Molecular Weights Showing Adequate Mechanical and Adhesion Properties and Fast Self-Healing at Room Temperature.

Dynamic non-covalent interactions between polycarbonate soft segments have been proposed for explaining the intrinsic self-healing of polyurethanes synthesized with polycarbonate polyols (PUs) at 20 °C. However, these self-healing PUs showed insufficient mechanical properties, and their adhesion properties have not been explored yet. Different PUs with self-healing at 20 °C, acceptable mechanical properties, and high shear strengths (similar to the highest ones reported in the literature) were synthesized by using blends of polycarbonate polyols of molecular weights 1000 and 2000 Da (CD1000 + CD2000). Their structural, thermal, rheological, mechanical, and adhesion (single lap-shear tests) properties were assessed. PUs with higher CD1000 polyol contents exhibited shorter self-healing times and dominant viscous properties due to the higher amount of free carbonate groups, significant carbonate-carbonate interactions, and low micro-phase separation. As the CD2000 polyol content in the PUs increased, slower kinetics and longer self-healing times and higher mechanical and adhesion properties were obtained due to a dominant rheological elastic behavior, soft segments with higher crystallinities, and greater micro-phase separation. All PUs synthesized with CD1000 + CD2000 blends exhibited a mixed phase due to interactions between polycarbonate soft segments of different lengths which favored the self-healing and mobility of the polymer chains, resulting in increased mechanical properties.

Ablation treatment of CFRP via nanosecond pulsed Ytterbium-doped fiber laser: Effects of process parameters on surface morphology and shear strength of adhesive bonded joints

Adhesive bonding is the joining technique that provides the maximum exploitation of Carbon Fiber Reinforced Polymers (CFRPs) for structural applications. However, it is necessary to attain a high-strength adhesive bond, achieved by removing surface contaminants, such as mold release agents, and simultaneously generating a surface structure suitable to increase the actual contact surface area. The purpose of the research work presented in this paper is to evaluate the effect of process parameters of a nanosecond pulsed laser pre-bonding surface treatment on the ablation of thermoset matrix CFRP substrates. In particular, the link between the volume of ablated material and the tensile shear strength (TSS) of adhesive bonded joints was evaluated by lap-shear tests, profilometer surveys, and Scanning Electron Microscope (SEM) analysis. ANOVA and regression models were used to highlight the influence of laser parameters, with power emerging as the most significant factor, and energy density proving pivotal for joint strength. Line spacing was also significant, while scanning direction had negligible impact. The key outcomes of the study demonstrated that controlled laser ablation plays a critical role in determining joint performance. A negative correlation was found between TSS and the thickness of ablated material, indicating that excessive ablation weakens the bond. Optimal joint strength was achieved with moderate fiber exposure while maintaining matrix integrity, emphasizing the need for precise control over laser parameters. Fracture surface analyses revealed distinct failure mechanisms, ranging from cohesive failure within the adhesive layer to interfacial failure at the fiber-matrix boundary, depending on the ablation conditions. The findings provide clear guidelines for optimizing laser surface treatments to enhance the structural performance of CFRP adhesive joints in practical applications.

Investigation of different process routes for joining thermoplastic composite/steel joints via the embedding of cold formed metallic pin structures

This study focuses on the integration of continuous fiber-reinforced thermoplastics (CFRT) with metal components through the use of cold-formed pin structures. Comparing six different joining methods with varying heat generation approaches, we investigated their impact on the mechanical properties and joint integrity. Ultrasonic vibration emerged as a highly promising method, offering both rapid joining operations and favorable mechanical characteristics with average failure loads in lap shear tests of up to 249 N. In comparison, vibration welding showed drawbacks, resulting in CFRT damage, potential pin failure, and diminished mechanical performance with maximum average lap shear loads of 216 N. Additionally, traces of zinc residue were identified on the CFRT surface, raising concerns about the corrosion resistance of the metal component. In summary, vibration welding appears unsuitable for pin joining applications. Infrared heating, while showcasing good mechanical performance with lap shear loads of up to 257 N, proved to be a more time-consuming process compared to ultrasonic joining. It also resulted in inferior mechanical strength under shear load in the direction of the fiber orientation (238 N). To assess the mechanical potential of pin joints relatively to established joining methods, we created and tested adhesively joined reference samples. Pin joints demonstrated a significant advantage under shear load, showing approximately double the shear strength (17.8 MPa) compared to adhesively joined samples (8.9 MPa). However, under normal load, pin joints exhibited lower strength, highlighting the need for further optimization to enhance their practical applicability.

Stress relaxation and improved fracture toughness of metal bonding using flexible monolith sheets and an epoxy adhesive

AbstractWhile epoxy resins exhibit excellent mechanical and insulating properties as well as excellent stability against heat and chemicals, epoxy adhesives also have drawbacks such as brittleness and stress concentration. Rubber-based materials are often added to epoxy adhesives to increase toughness, but they are sensitive to heat and moisture, limiting their effectiveness in harsh environments. In this study, we propose a new sheet-type adhesive consisting of a conventional liquid epoxy adhesive and an epoxy monolith sheet with internal continuous pores, using the advantageous properties of the flexibility and toughness of the epoxy monolith to avoid stress concentration. We evaluated the adhesion strength for metal bonding using the sheet-type epoxy adhesives via a lap-shear tensile adhesion test at various temperatures. The total destruction energy was also estimated via a tapered double cantilever beam test. Furthermore, a heat cycle adhesion test was conducted using two types of metallic materials with different coefficients of thermal expansion to elucidate the effect of the monolith sheet on the improvement of interfacial failure induced by stress concentration.

Comparative Study on the Effect of External Magnetic Field on Aluminum Alloy 6061 and 7075 Resistance Spot-Welding Joints

This study investigates the effects of the external magnetic field on the microstructure and mechanical property aluminum alloy 6061-T6 and 7075-T651 resistance spot welding joints. The melting behavior of 6061 and 7075 was analyzed via the calculation of the phase diagram (CALPHAD) technique. The CALPHAD results indicate that, for the 6061 aluminum alloy, the liquid fraction shows a minimal increase at the beginning stage during the solid–liquid phase transition process but with a sharp rise at the ending stage (near the liquidus). In contrast, for the 7075 aluminum alloy, the liquid fraction gradually increases throughout the entire solid–liquid phase transition process. The differences in melting behavior between the 6061 and 7075 alloys lead to different liquation crack morphologies in their spot-welded joints. In the 6061 alloy, the cracks tend to be “eyebrow-shaped”, allowing the liquid metal in the nugget to feed the gaps, and this does not significantly compromise the mechanical properties of the joint. In contrast, the 7075 alloy develops slender cracks that extend through the partially melted zone (PMZ), making it difficult for the liquid metal to feed these gaps, thereby significantly deteriorating the joint’s mechanical strength. Compared to conventional resistance spot-welding joints, the heat exchange between the nugget and the workpiece is enhanced under the external magnetic field, leading to a wider PMZ. This exacerbates the detrimental effects of liquation cracks on the mechanical properties of the 7075 joints. Lap-shear tests indicate that the mechanical properties of the 6061 aluminum alloy joints are improved under electromagnetic stirring. For 7075 aluminum alloy joints, the mechanical properties improve when the welding current is below 34 kA. However, when the welding current exceeds 34 kA, because the widening of the PMZ increases the tendency for liquation cracks, the joint’s mechanical property is deteriorated.

A coating with hydrogel@nanostructure on Ti surfaces via controllable Nano-mechanical interlocking

The elasticity mismatch between Ti and tissue limits the performance of Ti medical devices. How to create a coating with mimicking natural soft tissue stiffness and possessing strong mechanical bond is a challenge in implant manufacturing. Here, we developed a combined coating, that is, an anodized Ti surface (ATS) with nanostructures coated with a layer of PAAm hydrogel with tunable elasticity. Due to the nano-mechanical interlocking and hydrogen bonding synergy, the PAAm hydrogel layer was tightly anchored in nanostructures on the ATS. By regulating the oxidation voltage, nanostructures including nanopores, nanotubes, and punch-through nanotubes were fabricated on the ATS, and these three kinds of anodized nanostructures increase the porosity of the ATS sequentially. The lap shear test has shown that the shear strength increases linearly with increasing the porosity, and the shear strength of the punch-through nanotube structures with the PAAm hydrogel coating reaches 59.28 kPa. The adhesion mechanism between the anodized Ti nanostructures and the PAAm hydrogel coating is mainly due to the nano-mechanical interlocking and hydrogen bonding synergy, which was proven by morphology analysis, XRD, and ATR-FTIR characterization of the samples subjected to lap shear load. The hydrogel-nanostructures coating has demonstrated the potential to be applied in Ti medical devices.

Polyester Adhesives via One-Pot, One-Step Copolymerization of Cyclic Anhydride, Epoxide, and Lactide.

Polyesters (PEs) are sustainable alternatives for conventional polymers owing to their potential degradability, recyclability, and the wide availability of bio-based monomers for their synthesis. Herein, we used a one-pot, one-step self-switchable polymerization linking the ring-opening alternating copolymerization (ROAC) of epoxides/cyclic anhydrides with the ring-opening polymerization (ROP) of L-lactide (LLA) to synthesize PE-based hot-melt adhesives with a high bio-based content. In the cesium pivalate-catalyzed self-switchable polymerization of glutaric anhydride (GA), butylene oxide (BO), and LLA using a diol initiator, the ROAC of GA and BO proceeded whereas the ROP of LLA simultaneously proceeded very slowly, resulting in a copolyester consisting of poly(GA-alt-BO) and poly(L-lactide) (PLLA) segments with tapered regions, that is, PLLA-tapered block-poly(GA-alt-BO)-tapered block-PLLA (PLLA-tb-poly(GA-alt-BO)-tb-PLLA). Additionally, a series of tapered-block or real-block copolyesters consisting of poly(anhydride-alt-epoxide) (A segment) and PLLA (B segment) with AB-, BAB-, (AB)3-, and (AB)4-type architectures of different compositions and molecular weights were synthesized by varying the monomer combinations, alcohol initiators, and initial feed ratios. The lap shear tests of these copolyesters revealed an excellent relationship between the adhesive strength and polymer structural parameters. The (AB)4-type star-block copolyester (poly(GA-alt-BO)-tb-PLLA)4 exhibited the best adhesive strength (6.74 ± 0.64 MPa), comparable to that of commercial products, such as PE-based and poly(vinyl acetate)-based hot-melt adhesives.

Correlations between adhesion and molecular interactions at buried interfaces of model polymer systems and in commercial multilayer barrier films.

Sum frequency generation vibrational spectroscopy (SFG) was applied to characterize the interfacial adhesion chemistry at several buried polymer interfaces in both model systems and blown multilayer films. Anhydride/acid modified polyolefins are used as tie layers to bond dissimilar polymers in multilayer barrier structures. In these films, the interfacial reactions between the barrier polymers, such as ethylene vinyl alcohol (EVOH) or nylon, and the grafted anhydrides/acids provide covalent linkages that enhance adhesion. However, the bonding strengths vary for different polymer-tie layer combinations. Here, using SFG, we aim to provide a systematic study on four common polymer-tie interfaces, including EVOH/polypropylene-tie, EVOH/polyethylene-tie, nylon/polypropylene-tie, and nylon/polyethylene-tie, to understand how the adhesion chemistry varies and its impact on the measured adhesion. Our SFG studies suggest that adhesion enhancement is driven by a combination of reaction kinetics and the interfacial enrichment of the anhydride/acid, resulting in stronger adhesion in the case of nylon. This observation matches well with the higher adhesion observed in the nylon/tie systems in both lap shear and peel test measurements. In addition, in the polypropylene-tie systems, grafted oligomers due to chain scission may migrate to the interface, affecting the adhesion. These by-products can react or interfere with the barrier-tie chemistry, resulting in reduced adhesion strength in the polypropylene-tie system.

Fracture mechanisms of Al-steel resistance spot welds: The role of intermetallic compound phases

This study explores the mechanical and metallographic characteristics of Al-Steel dissimilar resistance spot welds (RSW), with a particular focus on the intermetallic compound (IMC) phases and their impact on fracture mechanisms. Detailed metallographic analyses and novel miniature lap shear tests with in-situ Digital Image Correlation techniques were conducted to observe the crack propagation behavior. The findings revealed that the IMC phases significantly influence the crack path and fracture mechanisms, leading to variations in fracture energy. Specifically, three distinct IMC phases were identified at the weld interface, each exhibiting unique structural and mechanical properties, with corresponding fracture energies of approximately 0.03 kJ/m2, 1.1 kJ/m2, and 7.5 kJ/m2. These variations highlight the critical role of the IMC phase in determining the fracture behavior of the weld. The study further supported the development and validation of a finite element (FE) model, incorporating a Cohesive Zone Model to simulate debonding behavior and the Hosford-Mean fracture criterion to predict ductile fracture in the Al fusion zone, thereby successfully linking local material characteristics to mechanical properties.

Advancing laser transmission welding for additive manufacturing: A study of glass fiber reinforced polypropylene parts

Laser transmission welding (LTW) is a well-established technique for joining high-volume thermoplastic parts, such as automotive injection molded parts. For low-volume, prototype, and custom production, additive manufacturing is an emerging technology for producing complex thermoplastic parts. When compared to injection molding, the additive manufacturing process fused filament fabrication (FFF) results in an inhomogeneous structure with entrapped air within the volume. Additionally, the presence of short glass fibers in the polymer matrix leads to higher radiation scattering during the welding process. This paper presents a fundamental study of the weldability of additively manufactured fiber-reinforced parts. The specimens were fabricated using a FFF process with glass fiber-reinforced polypropylene (GF-PP). The study investigates the influence of layer thickness and line width of the FFF process on the optical transmittance. LTW-experiments were conducted using additively manufactured uncolored and black GF-PP samples. Lap shear test specimens were welded with a different energy per unit length. This research presents a process for welding additively manufactured GF-PP parts that can be used with optimized FFF-parameters to produce high-strength and durable prototypes or spare parts for the automotive industry. This research provides valuable insights into the process parameters and considerations required to achieve robust welds in additively manufactured thermoplastic parts, facilitating broader adoption of LTW in additive manufacturing contexts.

Investigation of Microstructure and Interfacial Reactions of Diffusion Bonding of Ni-Ti6Al4V Materials Joined by Using Ag Interlayer.

Due to its super plasticity, low weight, and high mechanical resistance properties, generally, Ti6Al4V is used for aeronautical applications. However, it has low resistance to plastic shearing. In addition, it has poor wear resistance. For these reasons, a lot of techniques have been developed to improve its wear resistance. Investigations of microstructure and interfacial reactions of diffusion bonding of Ni and Ti6Al4V materials have been performed experimentally. Ni samples were prepared with 50 ± 5 µm Ni powders in cylindrical shape. For diffusion bonding, Ag foil was used for improving the interlayer and connection quality. Nickel and its alloys can be joined by using some different processes, and the use of an interlayer can further facilitate the joining process and improve the joint quality. The experiments were carried out under the protected atmosphere. Argon gas was used for protection. The experiments were performed under 5 MPa pressure for 60 min duration at 850 °C, 900 °C, and 950 °C thermal conditions. Investigations of metallurgical structure occurring in the interface areas were examined by optic analysis of EDS, SEM, and X-ray. The strength of the joints was tested by lap-shear tests. From observations, the best quality of the coalescence at interfaces was indicated at elevated temperatures.

Fabrication of Hybrid Epoxy Composites (Joint Compound Adhesive) for Aluminum Substrate Applications and Their Evaluation for Mechanical Properties.

This research endeavor deals with the development of an epoxy hybrid nanocomposite using aliphatic diglycidyl ether of a bisphenol A (DGEBA) epoxy matrix. The formulation used the stoichiometric ratio of the curing agent and incorporated nanopigments such as zirconium and silica, along with other microfillers. We incorporated Zr and SiO2 nanoparticles and various other additives in the epoxy matrix and ensured homogeneous dispersion by using sonication methodology along with silane as a coupling agent. Aluminum molds were utilized to fabricate dumbbell-shaped ASTM standard samples for the testing of mechanical properties. The adhesive properties were evaluated through standard lap shear tests. Fourier transform infrared spectroscopy was utilized to analyze the cross-linking reaction of the epoxy moiety and the polyamidoamine adduct curing agent. Further characterization using field emission scanning electron microscopy, energy-dispersive spectroscopy, and high-resolution transmission electron microscopy confirmed the presence and uniform dispersion of the fillers and nanopigments. The results showed good enhancements in ultimate tensile strength, yield strength, and elastic modulus of 95.3, 162.1, and 425.4%, respectively, compared to formulations using only SiO2. The addition of ZrO2 and SiO2, along with various microfillers, such as talc and aluminum silicate, led to significant improvements in the mechanical properties. This study demonstrates the synergistic efficiency of combining SiO2 and ZrO2 along with microfillers, such as talc and aluminum silicate, in epoxy resin for diverse applications in the construction industry, where mechanical strength and substrate adhesion are crucial.

Laser heat conduction joining of polycarbonate and aluminum alloy

The present work demonstrates the laser heat conduction joining (LHCJ) of polycarbonate and aluminum alloy. The experiments are performed to examine the impact of scan speed and laser power on the joint’s strength and quality. The bonding between the substrates was assessed by examining the cross-section using a scanning electron microscope and conducting energy-dispersive X-ray spectroscopy. The fractured surfaces are inspected by an optical microscope to explore the bond morphology. A finite-element-based numerical model is developed for the estimation of interface temperature and validated with the experimental results. Results of lap shear tests show that the weld strength is significantly affected by the laser power, scan speed, interface temperature, and bubble area. Microscopic observations of the joint interface disclose bubble area and mechanical interlocking between polycarbonate and aluminum. Through X-ray photoelectron spectroscopy (XPS) analysis, it was discovered that the interface experiences chemical bonding facilitated by the formation of Al-O-C bonds, which effectively enhances the strength of the joint.

Delamination free forming of novel high interface strength metal-polymer laminates

A new class of metal-polymer-laminates, fabricated using wire mesh and “steel-chips” interlayer, is shown to have significantly high interface strength. A finite element model, calibrated using tensile, lap shear, and peel tests, is used to predict the deformation and failure of the laminates. Formability of the developed laminates is studied using the limiting-dome-height tests. The metal-polymer-laminates do not delaminate in any of the tests. A complete shift of forming-limit-curve towards biaxial-tension region is observed in strain-based forming limit diagram for the polymer side. Strain-path independent forming-limits are plotted in stress space, to negative the effect of non-proportional strain histories.

Quantitative design criterion for mechanical interface functionalization regarding adhesion strength in chemically pre-treated polymer-metal hybrids using fractal dimension

ABSTRACT Polymer-metal hybrids (PMH) are common lightweight materials, whereas adhesion between metal and polymer is largely determined by the metallic surface design. Approaches in interface functionalization comprise both, mechanical and chemical surface modification. Therefore, surface modification on aluminum EN AW-6082 has been conducted prior to thermal joining to glass-fiber reinforced polyamide 6. Laser beam machining with a variation of structure density was carried out to produce defined groove structures. In addition, chemical surface modification by Boehmite hot water treatment as well as organo-silane couple agents were realized. Subsequently, the joint strength was assessed in lap shear tests. In order to quantitatively correlate the features of surface structure to the joint strength, regression analysis considering different chemical states were conducted. Hereby, the surface structure was represented on the one hand by the structure density and on the other hand by the calculated fractal dimension on cross-sectional images. The results revealed that using both, mechanical and chemical surface modification by laser machining as well as silanization, not only added together but moreover acted beneficial to each other. In addition, the fractal dimension proved to be a promising design criterion for linear correlation of joint strength independent of the chemical state.

Bond-slip models on interfacial behavior between Fe-SMA and steel in hygrothermal environments

Strengthening the existing steel structures to enhance performance can prolong their service life and reduce carbon emissions. Previous studies have employed iron-based shape memory alloy (Fe-SMA) to adhesively and actively retrofit long-span steel bridges in practice, achieving satisfactory repair efficiency. Nonetheless, concerns persist regarding the long-term performance of Fe-SMA-bonded parent structures, principally stemming from the performance degradation of the adhesives in hygrothermal environments. In this study, the damage evolution and debonding mechanisms of Fe-SMA/steel single-lap joints (SLJs) in hygrothermal environments are investigated through 54 lap-shear tests. The evolutionary process of Fe-SMA strain and shear stress within the overlapping zone is assessed, varying with aging time and adhesive type under shear load. Furthermore, the bond-slip models of the Fe-SMA/steel SLJs are put forward, which change with the aforementioned influencing factors in hygrothermal environments. The lap-shear tests demonstrate that the ultimate shear stress of SLJs is transmitted approximately up to 50 mm away from the initial end, with shear stress developing swiftly towards the free end during this phase. In hygrothermal environments, the effective overlapping length of the SLJs is highly contingent on the material properties of adhesives, improving with the prolonged aging time. This study proposes bond-slip models that describe the interfacial performance between Fe-SMA and steel, accounting for the detrimental influence of temperature, humidity, plastic deformation of components and strain relaxation. The experimental outcomes can guide the analysis of the debonding characteristics of Fe-SMA-bonded structures, and the theoretical study can provide reliable predictions for the service performance of reinforcement systems in hygrothermal environments.

Dissimilar impact spot welding of high-thickness aluminum-steel sheets using vaporizing foil actuators

The automotive industry’s shift towards multi-material structures necessitates efficient joining of aluminum and steel, yet techniques for high-thickness (>2 mm) dissimilar AA6XXX-HSLA steel pairs, remain underexplored. This study explores vaporizing foil actuator welding for spot welding 2.5 mm AA6111-HSLA 340 steel pairs, demonstrating successful joint formation via lap-shear testing and microscopy. Post-weld heat treatment influences joint strength and fracture behavior, with intermetallic compound (IMC) formation at the weld interface affecting mechanical properties. IMC cracking is observed in heat-treated samples. Fracture analysis reveals material transfer and secondary brazing action outside the weld zone. VFAW lap-shear failure loads outperform other joining techniques.