Search Results (297)

Single-lap shear joints made from fabric T300/polyphenylene sulfide (T300/PPS) and unidirectional T700/low-melt polyaryletherketone (T700/LM-PAEK) laminates are joined via induction and conduction welding at different processing temperatures. The joints are tested experimentally to investigate the influence of the processing temperature on the damage evolution in the specimens which is tracked using digital image correlation. Cracks grow rapidly in the unwelded parts of the joint interface but assume a stable steady-state propagation rate when reaching the fully welded overlap region. It is found that higher welding temperatures lead to longer weld lengths, which improve the strength and stiffness of the specimens and delay damage initiation. An accelerated crack growth rate indicates that the structure is close to its ultimate load after which the joint fails abruptly as the crack growth becomes unstable. Induction welding temperatures at the upper end of the recommended processing window (330 C for T300/PPS and 385 C for T700/LM-PAEK) result in the joints with the highest load-carrying capacity and slowest crack propagation, but also the least damage tolerance. Full article

Concrete structures are highly vulnerable to fire exposure, which accelerates the degradation of mechanical properties and may lead to partial or total structural failure. Externally bonded carbon fiber-reinforced polymer (CFRP) systems are widely used for post-fire strengthening; however, the bond behavior at the interfaces between CFRP and fire-damaged concrete, particularly under different cooling conditions, is not yet fully understood. In this study, the bond behavior was investigated experimentally and theoretically. Double-lap joint tests of thirty-nine specimens were conducted, including three unheated control specimens and thirty-six specimens exposed to temperatures of 200 °C, 400 °C, and 600 °C for durations of one and two hours. Two cooling methods, natural air cooling and water cooling, were applied prior to CFRP bonding. The results indicated that bond strength increased under exposure conditions of no more than 400 °C, whereas a significant reduction was observed at 600 °C. Water cooling resulted in lower bond strength compared with air cooling, while longer exposure durations improved bond performance under certain thermal conditions. The reasons behind the phenomena were analyzed in detail. Based on the experimental results, an analytical model for predicting the bond strength at the interfaces between fire-damaged concrete and CFRP sheets was developed. The model can account for the effects of peak temperatures, exposure durations, and cooling methods, and demonstrated high predictive accuracy (R² = 0.94). The findings provide valuable insight into CFRP–concrete interaction after fire exposure and offer practical guidance for the assessment and rehabilitation of fire-damaged concrete structures. Full article

One promising innovative joining process for non-oriented electrical sheets is based on an electro-insulating layer combined with a self-bonding varnish. The aim of this study was to investigate the adhesion of the self-bonding varnish as evaluated by a lap-shear test. During the experiments, non-oriented electrical steels with low to high silicon content were analyzed and tested. The Si content, the bond thickness, and the surface roughness Ra, as well as the selected steel production parameters—such as the radiation tube furnace temperature (RTF), the grain growth temperature (i.e., heating temperature (HF)), the peak metal temperature (PMT), and the annealing atmosphere (dry or humid, controlled by dew point)—were considered as the variables. The results showed that the lap-shear strength was independent of the surface roughness within the investigated range. In contrast, the bond thickness exhibited a weak positive effect on the lap-shear strength, while the Si content showed condition-dependent behavior. The RTF and the HF resulted in a relatively stable mechanical performance, whereas the PMT and the humid annealing atmosphere were identified as critical factors influencing adhesion. Full article

Bioadhesive materials capable of operating under aqueous conditions are of considerable interest for biomedical and materials science applications. Peptide-based systems represent an attractive platform for such materials due to their structural tunability, inherent biocompatibility, and ability to form supramolecular networks through noncovalent interactions. In this work, a focused library of tyrosine-containing dehydropeptides was designed and synthesized to investigate how molecular architectures influence self-assembly, hydrogel formation and adhesive properties. The peptides were synthesized using a solution-phase Boc strategy and systematically varied with respect to N-terminal protection and C-terminal functionality. The N-protected dehydropeptides formed supramolecular hydrogels through multiple gelation triggers, including pH reduction and heating–cooling cycles. Rheological characterization confirmed the formation of viscoelastic networks with tunable mechanical properties, with storage moduli reaching tens of kilopascals depending on peptide structure. Scanning electron microscopy revealed dense fibrous nanostructures consistent with supramolecular hydrogel formation. The N,C-deprotected dehydropeptides displayed reduced gelation propensity but formed cohesive films with measurable adhesive performance toward hydrophilic substrates. Lap-shear tests demonstrated high shear strengths for the hydrophilic films, highlighting their structural robustness under stress. Overall, this study provides insights into the structure–property relationships governing tyrosine-containing dehydropeptide assemblies and demonstrates their potential as minimalistic building blocks for supramolecular adhesive materials. Full article

The valorization of agro-industrial byproducts as sources of functional polysaccharides is a promising strategy for developing sustainable materials. In this study, cellulose was extracted and purified from rice husk and apple pomace through sequential alkaline and bleaching treatments. Then it was chemically modified via TEMPO-mediated oxidation to obtain cellulose nanofibers (TOCNFs) with cellulose yields ranging from 23.8 to 32.4% for rice husk and 9.3–13.8% for apple pomace. Owing to its higher recovery and structural regularity, rice husk was selected for surface modification with 3-aminopropyltriethoxysilane (APTES). The resulting TOCNFs exhibited an average width of 8 nm and a carboxyl content of 0.48 mmol g⁻¹. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and nitrogen determination (1.72 mg g⁻¹) confirmed the presence of aminosilane functionalities. APTES-modified TOCNFs were incorporated as active components to develop hybrid poly(vinyl acetate) (PVA) adhesives synthesized via in situ heterogeneous water-based polymerization. The influence of TOCNF surface chemistry and sodium dodecyl sulfate (SDS) on latex particle size, rheological behavior, and adhesive performance was systematically investigated. Latex particle size increased from 193 nm (PVA-SDS) to 625 nm with TOCNF-APTES and decreased to 247 nm upon SDS addition. Rheological analysis revealed pronounced shear-thinning behavior associated with the formation of percolated nanofibrillar networks, with low-shear viscosity increasing up to 477 Pa·s for TOCNF–APTES and decreasing to 370 Pa·s with SDS. Lap-shear testing (ASTM D905) showed substantial improvements in adhesive strength, reaching up to 250 kPa compared to PVA-SDS. These results demonstrate that surface-modified CNFs act not only as mechanical reinforcements but also as interfacially active components governing polymerization behavior, rheology, and adhesive performance. This exploratory study provides a proof-of-concept for the development of sustainable wood adhesives from agro-industrial byproducts. Full article

The applicability of two different joining processes for producing lap joints from high-strength steel sheets is investigated, reflecting their increasing use in advanced lightweight structures with demanding performance requirements. The work is primarily focused on the joining-by-forming process known as double-flush riveting, evaluated in two variants: one utilizing forged holes and the other employing machined holes. The performance of these two variants is compared with conventional fusion-based resistance spot welding using lap joints fabricated from 2 mm high-strength low-alloy S500MC steel sheets under varying geometric and process conditions, with support from finite element modelling. Results indicate that both double-flush riveting variants produce similar joint cross-sectional geometries, but the machined hole variant simplifies sheet preparation and eliminates the need for a progressive tooling system. Tensile lap-shear and peel test results reveal that double-flush riveted joints with forged holes exhibit superior strength, attributed to strain hardening in the forged regions. Furthermore, for nuggets and rivets of equivalent size, both double-flush riveting variants surpass resistance spot welding in terms of the mechanical strength of the final joints. These results suggest that double-flush riveting represents a promising alternative for assembling high-strength steel sheets in lightweight structural applications. Full article

Flax Fiber Reinforced Polymer (FFRP), as a green material with nonlinear large deformation characteristics, is used in the reinforcement of timber structures. Due to the similar elastic moduli of FFRP, adhesive, and timber, stress concentration at the interface is significantly reduced, demonstrating favorable interfacial performance. This study investigates the effects of adhesive layer thickness and FFRP laminate thickness on the strain distribution, bond-slip relationship, and stress distribution at the FFRP-timber interface through two different types of single-lap shear tests, thereby revealing the bonding mechanism at the FFRP-timber interface. The results show that both the ultimate load and the ultimate strain at the loaded end decrease with increasing adhesive thickness. For instance, increasing the adhesive thickness from 0.5 mm to 3 mm led to a 68.6% reduction in peak interfacial shear stress. The thickness of the adhesive has a minor influence on the overall trend of the bond-slip relationship curve for the FFRP-timber interface, with the curve consisting of an ascending branch, a descending branch, and a horizontal plateau. The distribution patterns of interfacial shear stress for different adhesive layer thicknesses are similar: at the initial loading stage, the maximum shear stress appears at the loaded end and gradually decreases toward the free end; as the load increases, the peak shear stress shifts from the loaded end toward the free end. With an increase in the number of fiber layers in the FFRP laminate, the strain transfer efficiency first increases and then decreases, reaching its maximum when the number of fiber layers reaches 30. The maximum stress increases with the number of FFRP fiber layers, and the stress transfer efficiency peaks at 30 layers. Full article

This research work addresses the mechanical and metallurgical characterisation, as well as the failure features, of two types of lap-fillet autogenous laser-welded joints made of ultra-thin sheets by applying an appropriate welding technology for producing sound welds and flawless joints. Both welded samples, one made only of stainless steel (SS-SS) sheets, and the other made of stainless steel and carbon steel (SS-CS) plates, were subjected to tensile–shear loads that are representative of the in-service conditions. The experimental research was focused on determining, by the digital image correlation (VIC-2D) method, the strain field and the rotation angle of the welded joints that were developed during loading tests of the welded specimens. Comparing to the classical testing method applied to study the joint overall mechanical properties, the novelty of this research consists of local mechanical behaviour assessment of relevant zones from similar and dissimilar welded joints, by using the innovative technique VIC-2D. Based on the analysis of the experimental results, it was found that the maximum rotation angle is 2.5 times higher in the SS-SS similar welded joint, in comparison with the SS-CS dissimilar welded joint. Despite this finding, the SS-CS specimen failed in the CS base material, far from the weld, with the failure phenomenon being preceded by the material yielding and necking. This failure mode is consistent with the detected strength mismatch of the SS-CS joint, with respect to the CS base material. In contrast, the quasi-ductile fracture of the SS-SS welded joint occurred by plastic exhaustion at the boundary between the narrow Heat-Affected Zone (HAZ) of SS and the Fuzion Zone (FZ). These outcomes are consistent with the hardness profile, microstructural heterogeneities found in the lap-fillet welded joints, and the load versus elongation curves that are determined and discussed in this paper. This research provides new insight and original information on the materials’ response to the autogenous laser welding, which will contribute to improving the knowledge on the ultra-thin lap-fillet welded similar and dissimilar steels. Full article

Adhesive bonding has emerged as a promising technology for joining carbon fiber reinforced polymer (CFRP) structures in aircraft, offering advantages over traditional mechanical fastening such as weight reduction and uniform stress distribution. This study evaluates the effectiveness of innovative laser ablation and electrospinning surface treatments compared to the conventional peel-ply method for secondary bonding. Surface features and wetting behavior were characterized using scanning electron microscopy (SEM) and contact angle measurements, while mechanical performance was assessed via single lap shear tests. Results demonstrate that laser ablation (30 W power, 10 m/s speed) achieved the highest bond strength at 20.68 MPa, followed by electrospinning (18.20 MPa) using 10 wt% PA-66 nanofibers. Both advanced techniques significantly outperformed the peel-ply method, which yielded the lowest shear strength of 15.18 MPa. SEM analysis confirmed that laser treatment facilitated direct fiber exposure with minimal damage, while nanofibers provided enhanced physical interlocking. In conclusion, laser ablation proved to be the most effective technique for enhancing interfacial bonding in aerospace-grade CFRP structures, followed by electrospinning, offering a superior alternative to traditional surface preparation. Full article

Diaphragm walls are widely used for deep foundation pit support and permanent underground structures. The joints between adjacent panels are critical weak points, significantly influencing the overall deformation and stress distribution of the structure. To address the insufficient shear and tensile capacity of existing diaphragm wall joints, this study proposes a novel rigid joint incorporating retractable shear studs. The joint features a straightforward and constructible design, primarily comprising retractable shear studs, H-section steel, and shear stud pop-out limit plates. By withdrawing the limit plates inserted into the H-section steel, the retractable shear studs mounted on the web automatically extend along their axis, penetrating into the adjacent reinforcement cage to form an intrusive lap joint. This mechanism effectively enhances the integrity and load-bearing capacity at the joint. To validate its mechanical performance, large-scale specimens featuring this new joint were fabricated and subjected to shear and tensile tests. The experimental results demonstrate that, compared to traditional H-section steel joints, the peak shear and tensile strengths of the proposed joint are increased by approximately 10 times and 16 times, respectively. These findings fully verify the excellent mechanical performance of the novel diaphragm wall joint structure. Full article

This study examines the joining characteristics of Cu foil stacks to lead tabs using green-laser welding in the main-welding step of a sequential welding process for lithium-ion pouch cells. The influence of lap configuration, line and wobble seam strategies, and process parameters was systematically investigated in terms of bead morphology, mechanical performance, metallurgical characteristics, and electrical resistance. Under the present line-welding parameter window (2.0 kW, 100–200 mm/s), humping, pinholes, and porosity were observed, particularly in the upper lead-tab configuration, which is attributed to melt-pool/keyhole instability under the applied conditions. Wobble welding effectively suppressed these defects in the foil-stack configuration by promoting stable melt flow and efficient bubble expulsion. Mechanical tests revealed that the wobble-based seam strategy achieved a maximum tensile–shear load of approximately 1.28 kN at a wobble amplitude of 0.8 mm. Fracture analysis confirmed a transition from seam-type interfacial failure in line welding to ductile tearing in the heat-affected zone with wobble welding. In electrical performance, wobble welding reduced resistance to as low as 45 µΩ at a wobble amplitude of 1.2 mm, while line welding yielded higher and scattered values. These results should be interpreted as the combined outcome of the wobble-based seam strategy (beam oscillation together with overlapped stitch welding at a lower travel speed) under the present processing windows. A strictly matched A/B comparison at identical linear energy density and seam layout will be investigated in future work to isolate the effect of oscillation. Full article

Biopolymer adhesives are moving toward frontline use in medicine and manufacturing as the limitations in some petrochemical systems, including cytotoxicity, challenges in wet adhesion for specific families of synthetic resins and formaldehyde emissions associated with amino-formaldehyde materials are becoming increasingly difficult to accept. This review integrates mechanisms, material classes and quantitative performance across biopolymer-based adhesives. We focus on architectures that combine permanent covalent anchoring with reversible, energy-dissipating bonds and on how functional group density, crosslink density, microstructure and additives act as design knobs for wet performance, durability and degradation. Across biomedical applications, chitosan, alginate, gelatin and related hydrogels achieve wet lap-shear strengths on the order of tens of kilopascals, cut liver-bleeding times by roughly half, provide strong antibacterial activity and close diabetic wounds by about 92 percent by day 14. Thermoresponsive alginate–gelatin sealants exceed clinically relevant burst pressures and microneedle patches withstand more than 120 mmHg while sealing arteries in under a minute. In industrial settings, dialdehyde-based starch resins deliver 0.83 to 1.05 MPa dry shear and maintain strength after water immersion while meeting stringent emission classes, and silane-modified nanocellulose in urea–formaldehyde markedly reduces free formaldehyde without sacrificing the internal bond. We conclude by identifying priorities for standardized wet testing, and lifetime matching of strength and degradation that can support large-scale clinical and industrial translation. Full article

Background: Durable bonding to zirconia remains difficult because its chemically inert surface resists acid etching. Additive manufacturing (AM) enables controlled surface morphology, which may enhance micromechanical retention without additional treatments. Methods: Zirconia specimens with three AM-derived surface designs—(1) concave–convex hemispherical patterns, (2) concave hemispherical patterns, and (3) as-printed surfaces—were fabricated using a slurry-based 3D printing system and sintered at 1500 °C. Zirconia specimens fabricated by subtractive manufacturing using CAD/CAM systems, polished with 15 µm diamond lapping film and with or without subsequent alumina sandblasting, served as controls. Surface morphology was analyzed by FE-SEM, and shear bond strength (SBS) was tested after cementation with a resin-based luting agent. Results: SEM revealed regular layered textures and designed hemispherical structures (~300 µm) in AM specimens, along with step-like irregularities (~40 µm) at layer boundaries. The concave–convex AM group showed significantly higher SBS than both sandblasted and polished subtractive-manufactured zirconia (p < 0.05). Vertically printed specimens demonstrated greater bonding strength than those printed parallel to the bonding surface, indicating that build orientation affects resin infiltration and interlocking. Conclusion: AM-derived zirconia surfaces can provide superior and reproducible micromechanical retention compared with conventional treatments. Further optimization of printing parameters and evaluation of long-term durability are needed for clinical application. Full article

Sintered nano-silver is widely investigated as a die-attach material for next-generation power electronic modules due to its high thermal conductivity, favorable electrical performance, and stability at elevated temperatures. However, how bonding pressure and joint thickness jointly affect densification, interfacial diffusion, and mechanical reliability has not been systematically clarified, especially under the low-pressure conditions required for large-area SiC and GaN devices. In this work, nano-silver lap-shear joints with three bond-line thicknesses (50, 70, and 100 μm) were fabricated under two applied pressures (1.0 and 1.5 MPa) using a controlled sintering fixture. Shear testing and cross-sectional SEM were employed to evaluate the relationships between microstructural evolution and joint integrity. When the bonding pressure was increased from 1.0 to 1.5 MPa, more effective particle rearrangement and reduced pore connectivity were observed, together with improved metallurgical bonding at the Ag–Au interface, leading to a strength increase from 15.3 to 28.2 MPa. Although thicker joints exhibited slightly higher bulk relative density due to greater heat retention and accelerated local sintering, this densification advantage did not lead to improved mechanical performance. Instead, the lower strength of thicker joints is attributed to a narrower Ag–Au interdiffusion region, which limited the formation of continuous load-bearing paths at the interface. Fractographic analyses confirmed that failure occurred predominantly by interfacial delamination rather than cohesive fracture, indicating that the reliability of the joints under low-pressure sintering is governed by the quality of interfacial bonding rather than by overall densification. The experimental results show that, under low-pressure sintering conditions (1.0–1.5 MPa), variations in bonding pressure and bond-line thickness lead to distinct effects on joint performance, with the extent of Ag–Au interfacial interaction playing a key role in determining the mechanical robustness of the joints. Full article

Adhesive joint failure remains a critical limitation in the manufacturing of large wind turbine blades, where reliable and reproducible surface preparation methods are required at an industrial scale. This study systematically evaluates the effect of peel ply-induced surface morphology and chemistry on the adhesion performance of glass fiber-reinforced polymer (GFRP) laminates, explicitly examining the relationship between wettability and bonding strength. Five surface conditions were generated during vacuum-assisted resin infusion using different commercial and proprietary peel plies and a smooth mold surface. Despite significant differences in contact angle and surface energy, lap shear testing revealed no significant relationship between wettability and joint strength. Instead, surface roughness-driven mechanical interlocking and adhesive–substrate compatibility dominated performance. Compared to the smooth mold surface, twill-type peel ply–modified adherends increased shear strength by up to 3.9×, while other commercial types of peel-plies presented strength improvements between 2.7 and 3.3×. More compatible adhesive–polymer resin systems exhibited a combination of cohesive and adhesive failures, with no clear dependence on surface roughness. In contrast, when the adhesive is less compatible with the substrate, surface roughness significantly affects the adhesive response, with adhesive failure predominating. The adhesive application temperature showed no measurable effect for practical industrial use. These findings demonstrate that wettability alone is not a reliable predictor of adhesion performance for this class of substrates and confirm peel ply surface modification as a robust, scalable solution for industrial wind blade bonding. Full article