Search Results (23)

The failure behaviors of CFR–aluminum lap joints with diverse configurations through quasi-static tensile tests were conducted at −40 °C, 25 °C, and 80 °C. Four specimen types were examined: CFRP–aluminum alloy two-bolt single-lap joints (TBSL), two-bolt double-lap joints (TBDL), two-bolt bonded–bolted hybrid single-lap joints (BBSL), and two-bolt bonded–bolted hybrid double-lap joints (BBDL). The analysis reveals that double-lap joints possess a markedly higher strength than single-lap joints. The ultimate loads of the TBSL (single-lap joints) at temperatures of −40 °C and 25 °C are 29.5% and 26.20% lower, respectively, than those of the TBDL (double-lap joints). Similarly, the ultimate loads of the BBSL (hybrid single-lap joints) at −40 °C, 25 °C, and 80 °C are 19.8%, 31.66%, and 40.05% lower, respectively, compared to the corresponding data of the TBDL. In bolted–bonded hybrid connections, the adhesive layer enhances the joint’s overall stiffness but exhibits significant temperature dependence. At room and low temperatures, the ultimate loads of the BBDL are 46.97 kN at −40 °C and 50.30 kN at 25 °C, which are significantly higher than those of the TBDL (42.24 kN and 44.63 kN, respectively). However, at high temperatures, the load–displacement curves of the BBDL and TBDL are nearly identical. This suggests that the adhesive layers are unable to provide a sufficient shear-bearing capacity due to their low modulus at elevated temperatures. This research provides valuable insights for designing composite–metal connections in aircraft structures, highlighting the impacts of different joint configurations and temperature conditions on failure modes and load-bearing capacities. Full article

Timber–steel hybridisation offers a balanced approach by capitalising on the high strength-to-weight ratio and sustainability of the timber while also benefiting from the high stiffness and ductility of the steel, contributing to the improved performance of hybrid structural elements. This paper reviews key aspects of timber–steel hybridisation, with a particular emphasis on the connection methods between timber and steel, including adhesive bonding and mechanical fastening, as well as the different types of reinforcement configurations. In particular, this review covers two main types of adhesives used in timber–steel hybrid systems, namely, epoxy and polyurethane, and two primary types of mechanical fasteners, namely, bolts and screws. The mechanical performances of all hybridisation methods are reviewed. The importance of surface treatments, such as shot blasting for steel and mechanical abrasion for timber, is also discussed as a key factor in optimising adhesive bonds. Furthermore, various reinforcement configurations, including top, bottom, side, and embedded arrangements, are evaluated for their impact on the structural efficiency and fire performance. To support this evaluation, calculations have been carried out to illustrate how different reinforcement configurations influence the stress distribution in timber–steel hybrid beams. By providing detailed insights into these critical aspects, this paper serves as a valuable decision-making tool, offering guidance for researchers and industry professionals for selecting the appropriate bonding techniques and configurations to meet specific structural objectives and advance sustainable construction practices. Full article

The IDEA project, developed in the frame of MOST—National Centre for Sustainable Mobility—addressed the growing need for reliable bonded joints in fibre-reinforced polymer composite structures used in transportation. Purely bonded joints are preferred for their lightweight and cost-efficient properties, but contamination and defect detection issues often make them unreliable. To solve this, the project developed innovative surface treatments, a methodology for the safe, optimized design of bonded joints, and structural health monitoring solutions, viable for real-time assessment. These advancements aim to increase the reliability and safety of bonded connections, helping industries adopt lighter, purely bonded joints over heavier, hybrid bonded/bolted options. Full article

Glass fiber-reinforced polymer (GFRP) connecting joints are difficult in the design of structural components and also critical areas prone to damage. In this study, based on the existing research, a combination of experimental and finite element analysis is used to systematically analyze the performance-influencing factors of the hybrid connection of glass fiber-reinforced composite plate and steel plate adhesive bolts under tension. By discussing the damage modes, load–displacement curves, and strain distributions at the GFRP connection joints, the influence of the connection methods and bolt quantities on the tensile properties of double-lap joints comprising GFRP plates and steel plates is revealed, and a loss evolution model for GFRP composite plates is established based on the Hashin failure criterion. The results show that the adhesive–bolted connection integrates the advantages of both adhesive bonding and bolted connections, significantly improving the tensile performance of the joint. Furthermore, the vertical arrangement of two bolts is superior to the horizontal arrangement under double-bolt connection conditions between GFRP plates and steel plates. For the several design options proposed in this study, the GFRP joints exhibit the optimal tensile properties among the four bolt arrangement schemes. Full article

Straw–concrete combined floor slabs consist of straw boards, shear-resistant connectors, and concrete slabs. These slabs offer various advantages over traditional reinforced concrete slabs due to the straw boards’ properties of excellent insulation and sound absorption. Research using ABAQUS software created 15 composite floor models to study the impact of connection methods, bond strength, connector spacing, and thickness of straw and concrete on the flexural performance. Results indicated that the composite floor slab with adhesive bonding had a 7.34% and 17.34% higher load-carrying capacity than the bolt-connected and self-tapping screw-connected composite floor slabs, respectively. Increasing bond strength from 40 MPa to 60 MPa improved the load-carrying capacity of self-tapping nail-connected slabs by 80.84%. Connector spacing negatively correlated with slab capacity, while increasing the thickness of straw boards or concrete slabs enhanced the ultimate load-carrying capacity, with the latter having a more significant effect. Midspan deflection and flexural capacity were calculated using the converted cross-section method and static calculation formulas, with theoretical and simulated values showing good agreement, offering guidance for engineering applications. Full article

Vibration testing is crucial for understanding structural dynamics, yet conventional modeling of bolt connections often leads to significant inaccuracies. This study systematically compares six bolt connection methods—bonded, adaptive bonded, joint, beam, screw, and fixed bolt—using a finite element analysis of a headlamp vibration test jig. The six bolt connection methods were selected based on approaches adopted in previous studies. The experimental results identified the joint connection method as the most accurate, minimizing deviations in natural frequency to 7.6 Hz compared to experimental tests at 493.2 Hz, while bonded methods overestimated the frequency at 544.1 Hz due to excessive stiffness assumptions. Efficiency analyses highlighted bonded methods as the most computationally streamlined, offering preprocessing times as short as 30 s and shorter overall analysis times. These findings emphasize the importance of selecting appropriate bolt connection methods in the early design phase to ensure accurate natural frequency predictions and mode shape representations. Although this study does not consider bolt preload forces, the work shows the possibility of offering practical guidelines for improving the reliability and efficiency of vibration test jig designs by bridging the gap between analysis and experimental results. Full article

Mechanical joints, regardless of materials, are useful when joining multiple components, though there are certain limits when applying them in engineering applications such as fatigue loading. The purpose of this research is to provide a comprehensive review of the trend of fatigue properties of common non-thermal mechanical connections such as adhesive, bolted, clinched and riveted joints. Towards that, a narrative approach was taken. In modern engineering applications, most of the joints contain both metallic and non-metallic components. The relevant experimental studies have proven many factors that can affect each type of joint and how they can be implemented in real-time appliances. For instance, the fatigue behaviour of adhesive joints is affected by the bond length, thickness and the use of different materials. Increasing the bond length can enhance its fatigue resistance up to a certain length, whilst increasing the thickness of laminate or adhesive decreases the fatigue life unless the surface roughness increases. On the other hand, different laminate materials can affect the fatigue performance depending on their mechanical properties. These findings will allow readers to have an overall concept of the fatigue behaviour of mechanical joints and the influence of various internal and external parameters on that. Full article

The prestressed active reinforcement of concrete structures using iron-based shape memory alloys (Fe-SMAs) is investigated in this experimental study through three connecting methods: adhesive–bolted hybrid connection, bolted connection, and adhesively bonded connection by activating at elevated temperatures (heating and cooling) and constraining deformation to generate prestress inside Fe-SMAs, through which compressive stress is generated in the parent concrete structures. In tests, the Fe-SMA is activated at 250 °C using a hot air gun, generating a prestress of 184.6–246 MPa. The experimental results show that local stress concentration in the concrete specimen and Fe-SMA plate around the hole is caused by the bolted connection. The adhesively bonded connection is prone to softening and slip of the structural adhesive during the activation process, thereby reducing the overall recovery force of Fe-SMAs. The adhesive–bolted hybrid connection effectively mitigates the local stress concentration problem of concrete and Fe-SMAs at anchor holes, while avoiding the prestress loss caused by the softening and slip of structural adhesive during elevated-temperature activation, achieving good reinforcement effect. This study on the connection methods of an Fe-SMA for reinforcing concrete structures provides both experimental support and practical guidance for its engineering application, offering new perspectives for future research. Full article

Anchor bolts are often used in nuclear power plants to connect equipment and equipment foundations. Under a severe earthquake, tensile breakout failure is prone to occur in the anchor bolts. As the total amount of installed machines rises, the inertial forces transferred to the anchor bolts under seismic loads also increase significantly. Therefore, the capacity is no longer satisfied by concrete alone, and specialized supplementary reinforcement needs to be installed around the bolts. The study analyzed the tensile behavior of anchor bolts in foundations with supplementary reinforcement experimentally. A total of 16 single-headed anchors in RC foundations with various diameters, yield strengths, and forms of supplementary reinforcement were tested under monotonic tensile loading. The results show that supplemental tie bars and supplemental U-shaped bars, respectively, rely on the bond with the concrete and their own tensile strength to increase the tensile breakout capacity. Furthermore, based on the failure mechanism, a new model considering the terms of concrete resistance and reinforcement resistance for the tensile breakout capacity of headed anchors around with supplementary reinforcement was proposed. Compared with the strut–tie model by EN 1992-4:2018, the predicted results of the model proposed by this study are relatively consistent with the experimental results, while the results by EN 1992-4:2018 are overly conservative. Full article

The interface mechanical performance between aluminum alloy and timber is the key to ensure that the two work together. In this study, 11 group connection performance tests were carried out to investigate the influence of connection type (shear bolt connection, epoxy resin adhesive connection, and mixed connection), number and spacing of bolts, thickness, and length (the area of incidence of the adhesive in the structure) of epoxy resin adhesive on the interface shear-resistant capacity of aluminum–timber composite connections. The shear performance of the three kinds of connections were studied via finite element analysis, and the calculation formula for interface shear-resistant capacity of the aluminum–timber composite connection was proposed based on the bond-slip mechanism of adhesive. The analysis results indicate that the mixed connection can avoid the brittle failure characteristics of the shear bolt connection and the epoxy resin adhesive connection, and the shear-resistant capacity is increased by 45.6% and 14.7%, respectively. The results of the calculation formula for interface shear-resistant capacity are in good agreement with the experimental results, indicating that it is suitable for the aluminum–timber composite connection. Full article

CFRP hybrid bonded–bolted (HBB) joints combine the advantages of traditional joining methods, namely adhesive bonding, and bolting, to achieve optimal connection performance, making them the most favored connection method. The structural parameters of CFRP HBB joints, including overlap length, bolt-hole spacing, and fit clearance relationships, have a complex impact on connection performance. To enhance the connectivity performance of joint structures, this paper develops a multiscale finite element analysis model to investigate the impact of structural parameters on the strength of CFRP HBB joint structures. Coupled with experimental validation, the study reveals how changes in structural parameters affect the unidirectional tensile failure force of the joints. Building on this, an analytical approach and inverse design methodology for the mechanical properties of CFRP HBB joints based on deep supervised learning algorithms are developed. Neural networks accurately and efficiently predict the performance of joints with unprecedented combinations of parameters, thus expediting the inverse design process. This research combines experimentation and multiscale finite element analysis to explore the unknown relationships between the mechanical properties of CFRP HBB joints and their structural parameters. Furthermore, leveraging DNN neural networks, a rapid calculation method for the mechanical properties of hybrid joints is proposed. The findings lay the groundwork for the broader application and more intricate design of composite materials and their connection structures. Full article

Hybrid bonded–bolted composite material interference connections significantly enhance the collaborative load-bearing capabilities of the adhesive layer and bolts, thus improving structural load-carrying capacity and fatigue life. So, these connections offer significant developmental potential and application prospects in aircraft structural assembly. However, interference causes damage to the adhesive layer and composite laminate around the holes, leading to issues with interface damage. In this study, we employed experimental and finite element methods. Initially, different interference-fit sizes were selected for bolt insertion to analyze the damage mechanism of the adhesive layer during interference-fit bolt installation. Subsequently, a finite element tensile model considering damage to the adhesive layer and composite laminate around the holes post-insertion was established. This study aimed to investigate damage in composite bonded–bolted hybrid joints, explore load-carrying rules and failure modes, and reveal the mechanisms of interference effects on structural damage and failure. The research results indicate that the finite element prediction model considering initial damage around the holes is more effective. As the interference-fit size increases, damage to the adhesive layer transitions from surface debonding to local cracking, while damage to the composite matrix shifts from slight compression failure to severe delamination and fiber-bending fracturing. The structural strength shows a trend of initially increasing and then decreasing, with the maximum strength observed at an interference-fit size of 1.1%. Full article

The utilization and incorporation of glass fiber-reinforced plastics (GFRP) in structural applications and architectural constructions are progressively gaining prominence. Therefore, this paper experimentally and numerically investigates the use of GFRP I-beams in conjunction with concrete slabs to form composite beams. The experimental design incorporated 2600 mm long GFRP I-beams which were connected compositely to concrete slabs with a 500 mm width and 80 mm thickness. The concrete slabs are categorized into two groups: concrete slabs cast using normal-strength concrete (NSC), and concrete slabs prepared using high-strength concrete (HSC). Various parameters like the type of concrete (normal and high-strength concrete), type of stiffeners bonded to the composite section (bolt–epoxy or bolt only), and inclusion of corrugated metal sheets were investigated. To obtain the full shear connection between the GFRP I-sections and concrete slabs, two rows of shear connectors in the form of bolts were utilized. These shear connectors were erected to the top flange of the GFRP I-sections to compositely connect between the GFRP I-beams and the concrete slabs as well as the corrugated metal sheets. The strengthening of the shear webs of GFRP I-beams with GFRP T-section stiffeners resulted in an enhancement in the flexural and shear strength. The failure loads in the case of the bolt–epoxy connection for the stiffeners were 8.2% and 10.0% higher than those in the case of bolt only when the concrete compressive strengths were 20.1 MPa and 52.3 MPa, respectively. Moreover, the effect of the concrete compressive strength was vital where the failure loads increased by 79.9% and 77.1% when HSC was used instead of NSC for the cases of bolt–epoxy and bolt only, respectively. The epoxy adhesive used in conjunction with mechanical connectors, specifically bolts, resulted in sufficient composite action and delayed shear failure within the web of the GFRP beam. For the specimens with bolt–epoxy connection, strain levels in the concrete slabs were consistently higher than in the other specimens with bolts alone at the same loading level. The concrete slabs integrated with HSC registered strain levels that were 20.0% and 21.8% greater for bolt–epoxy and bolt-only connections, respectively, when compared to those using normal-strength concrete (NSC). This discrepancy can likely be credited to the enhanced composite interaction between the concrete slabs and the GFRP I-beams. In addition, ABAQUS software (version 6.2) was used to develop FE models to analyze the tested composite beams and provide a parametric study using the verified models. Full article

Although 3D printing technology has been applied worldwide, the problem of connecting a printed structure and a foundation has rarely been examined. In particular, loads in the horizontal direction, such as wind loads and earthquake loads, can significantly affect the stability of a printed structure. Therefore, in this study, the effect of lateral loads on printed columns that were connected to a foundation by two types of connectors was investigated. A steel angle with bolts and couplers was used to connect the printed column to a concrete footing. In addition, two types of lateral reinforcement were applied to the printed column to enhance its bonding strength and shear resistance. The lateral reinforcements were attached to the interface of the printed layers at distances of 100 and 200 mm to investigate the effect of lateral reinforcement distance on the lateral behavior of the printed column. The results showed that the use of couplers as connections between the columns and foundation significantly improved the load capacity. Furthermore, the effects of the lateral reinforcement types and lateral reinforcement distances were assessed. Full article

High−performance bolts made of carbon/carbon (C/C) composites are necessary for connecting thermally−insulating structural components of aerospace vehicles. To enhance the mechanical properties of the C/C bolt, a new silicon infiltration−modified C/C (C/C−SiC) bolt was developed via vapor silicon infiltration. The effects of silicon infiltration on microstructure and mechanical properties were systematically studied. Findings reveal that dense and uniform SiC−Si coating has been formed after silicon infiltration of the C/C bolt, strongly bonding with the C matrix. Under tensile stress, the C/C−SiC bolt undergoes a tensile failure of studs, while the C/C bolt is subject to the pull−out failure of threads. The breaking strength of the former (55.16 MPa) is 26.83% higher than the failure strength of the latter (43.49 MPa). Under double−sided shear stress, both the crushing of threads and the shear failure of studs occur within two bolts. As a result, the shear strength of the former (54.73 MPa) exceeds that of the latter (43.88 MPa) by 24.73%. According to CT and SEM analysis, matrix fracture, fiber debonding, and fiber bridging are the main failure modes. Therefore, a mixed coating formed by silicon infiltration can effectively transfer loads from coating to carbon matrix and carbon fiber, thereby enhancing the load−bearing capacity of C/C bolts. Full article