Hybrid Joints Research Articles

Robust ultrasonically welded CF/PEI-CF/epoxy composite joints upon tailoring the thermoplastic resin thickness at the welding interface

The objective of this study was to develop robust carbon fiber/epoxy (CF/epoxy)-carbon fiber/polyetherimide (CF/PEI) hybrid joint upon an ultrasonic welding process. The co-curing of a PEI coupling layer (CL) on the surface of the CF/epoxy composite makes it “meltable and weldable”. The CF/epoxy was then ultrasonically welded with the CF/PEI using different combinations of energy director (ED) and CL thicknesses. The results showed that high-quality welding line could be obtained by carrying out coupling-optimization to the thicknesses of the EDs and CLs using an optimal welding displacement. For example, a largest lap-shear strength (LSS) of 35.3 MPa was achieved when both of the ED and CL possessed an optimal thickness of 175 μm. In this case, a cohesive failure within either the CF/PEI or the CF/epoxy substrate took place during the single-lap shear test of the hybrid joints. Predictably, this study provides a promising strategy for the production of high-performance hybrid composite joints upon tailoring the thicknesses of the EDs and the CLs for the ultrasonic welding process.

Failure analysis of CFRP-aluminum electromagnetic self-pierce riveting-bonded joints subjected to highspeed loading

The mechanical performance of dissimilar material riveted joints is important for passenger safety during a crash situation. Hence, in this paper, the mechanical properties of CFRP-aluminum electromagnetic self-pierce riveting-bonded (E-SPR-bonded) joints under quasi-static and dynamic loading was investigated. First, the hybrid joints were manufactured under five discharge energies to explore the best process parameter, then, the effect of shearing speed on the mechanical properties were studied. Digital image correlation (DIC) method was carried out to further understand the surface strain distribution. Results indicated that the evolution of shear tests could be divided into two stages, including two peak loads, named peak A and peak B, respectively. The hybrid joint at 7.7 kJ had the best peak load during static load. Under the dynamic loading condition, the peak load increased with ascending load speed, especially the peak B, under 4, 8 and 12 m/s, were 189.0 %, 205.5 %, and 215 % higher than that of 2 mm/min, respectively. The hardening effect of sheets was increased under high shear speeds, which dominated the fracture behaviors of the bonding layer. The hybrid joints failure behavior was the CFRP fracture, and the rivet remained in the aluminum sheets. The results could provide theoretical guidance for the structural design of automobiles and promote its engineering application.

Study on the failure mechanism and mechanical properties of multi-layer hole-drilled self-piercing riveted three-layer steel/aluminum hybrid joints

To promote the application of the three-layer steel/aluminum hybrid sheet in the lightweight vehicle body, the multi-layer hole-drilled self-piercing riveting (MH-SPR) process is proposed. This paper aims to investigate the failure mechanism and mechanical properties of three-layer MH-SPR joints and explore the effects of overlap type and pre-drilled layer on forming quality, mechanical properties, failure modes, and fracture characteristics of the three-layer MH-SPR joint in detail. Three overlap types (e.g., type A, type B, and type C) and three pre-drilled layers (e.g., J0, J1, and J2) are designed for the experimental study and the shear experiments and full-field strain measurements are carried out. The results show that the pre-drilled layer can improve SPR joinability and reduce the peak force and energy consumption during the riveting process. Overlap types A and C can increase the peak force of the joint and type C can simultaneously enhance the peak force and energy absorption of the joint. The increase in the pre-drilled layer can increase the peak force and energy absorption of the joint. The overlap types and pre-drilled layers change the failure modes of the joints, which include five types of failure modes: middle sheet tearing, top sheet tearing, rivet fracture, interlock failure, and mixed failure. Full-field strain analysis shows that the overlap type improves the mechanical properties of the joints by altering the deformation mode of the steel sheet. This work provides a theoretical basis for expanding the industrial practice of the MH-SPR process and improving the joined quality of the three-layer joint.

A Multiscale Modeling and Experimental Study on the Tensile Strength of Plain-Woven Composites with Hybrid Bonded-Bolted Joints.

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.

Tensile-shear mechanical properties of friction stir spot weld bonding hybrid joint in welding prior to and after adhesive curing for vehicle using

This research proposed a temperature-controlled friction stir spot weld bonding process as a solution to the issues of adhesive carbonization and weld impurities in the traditional combination of friction stir spot welding and adhesive bonding. A comprehensive investigation was conducted, including the establishment of a simulation model using the DFLUX subroutine to analyze the welding temperature field and the implementation of an overflow groove to separate the weld from the adhesive. The microstructure and mechanical properties of the joint were examined in the joint of welding before and after the adhesive curing process. The results demonstrated significant improvements in the failure load of the hybrid joints, with increases of 57.4 % and 27.7 %, compared to the welding joint. Additionally, the failure mechanism of the hybrid joint was elucidated by analyzing the fracture morphology.

Enhancing mechanical properties of GFRP–aluminum joints through Z pinning: a low velocity shear impact study

Studying the mechanical responses of GFRP and aluminum samples under varying loads is crucial for developing methods to enhance their mechanical properties. This research investigates the impact of z-pinning on single-lap adhesive joints through low-velocity shear impact tests. The study involves testing two types of joints: single-lap adhesive joints and single-lap hybrid pin-adhesive joints with six reinforcing pins, subjected to drop weight tests at load levels of 22.5, 27.5, and 32.4 J. The findings demonstrate that z-pinning can increase the joints’ load-bearing capacity by up to 18.87% and energy absorption by 20.58%. This enhancement is attributed to the additional composite substrate layers in the hybrid joint, which help absorb impact loads. In contrast, in the single-lap adhesive joint, only the layer adjacent to the adhesive bears the impact load. Observations from the tests indicate that in the single-lap adhesive joint, the first composite layer next to the adhesive undergoes complete delamination, whereas in the hybrid joint, all laminates fracture at the steel pins. In summary, this study underscores the significant potential of z-pinning to improve single-lap adhesive joints, providing an innovative approach to enhance their load-bearing capacity and energy absorption.

Control of Structural Seismic Damage in Prefabricated Reinforced Concrete Frames through Hybrid-Selfcentering Connections

Current seismic design philosophy of industrial structures in Chile aims at the protection of life and continuity of operation in the industry. The compliance with these requirements allows controlling structural damage based on resistance criteria, without detecting the failure mode or specifying its location in the event of a major seismic event. In this paper, we discuss the application of an innovative technique for controlling the structural damage in prefabricated reinforced concrete frames, which are founded on granular soils. This technique is applied in the construction of the Forest and Paper Pulp Plant Concepción. This is done by incorporating hybrid post-tensioned joints in precast columns of the project, and this approach aims to control energy dissipation in the union and maintain the initial stiffness of the system. Using a nonlinear dynamic analysis with 2D Ruaumoko software, potential performance in traditional design versus innovative design is compared. The analysis is performed for various Chilean representative seismic records and different types of soils. The results indicate that the structure with the traditional design could suffer displacement in the roof of the order of 40 cm, moving heavily into the inelastic range, with residual deformations and concentrating the damage generation of plastic hinges at the ends of the columns and some beams not designed for ductility. In contrast, the use of self-centering hybrid joints causes the structure to recover its original position, without the presence of remnant deformations.

Finite Element Analysis of Seismic Performance of RCS Hybrid Joints of Steel Hoop Structure

Reinforced concrete column-steel beam (RCS) composite structures are widely used in super highrise buildings due to their excellent performance. In this paper, the numerical simulation analysis of the RCS hybrid joints of “beam through” and “column through” RCS constructed with steel hoop structure are carried out, and the influence of five different parameters, i. e. , flange width-thickness ratio, steel yield strength, axial compression ratio, concrete strength and end plate thickness, on the seismic performance and failure mode of RCS hybrid joints is investigated. The results show that the ABAQUS finite element model can simulate the performance of RCS mixing under static load through reasonable parameter settings, which is in good agreement with the experimental results. Under the mechanism of “strong column and weak beam”, the combined node firstly undergoes beam-hinge damage, and the change of the axial compression ratio and the concrete strength parameter of the joint have little effect on the ultimate bearing capacity and deformation performance of the joint. Increasing the flange width-thickness ratio reduces the bearing capacity of the joint by up to 11%, and increases the yield strength of the steel, and increases the bearing capacity of the joint by 36. 4%. The thickness of the end plate of the column through specimen is increased, and the bearing capacity and deformation performance of the joint are improved to a certain extent. The changes of each parameter have no significant effect on the final plastic hinge failure mode of the joint. The research in this paper provides theoretical support for the design and research of this type of node in the future.

Research on the Mechanical Properties of Single-Lap Rivet-Bonded Hybrid Joint Considering the Rivet Forming Process

Research on the Mechanical Properties of Single-Lap Rivet-Bonded Hybrid Joint Considering the Rivet Forming Process

Effect of Adhesive Layer Thickness on Strength of Carbon-Fiber-Reinforced Plastic/Aluminum Bond-Riveted Joints

This paper investigated the mechanical performance, progressive failure process, and failure modes of riveted joints, bonded joints, and hybrid joints with different adhesive layer thicknesses connecting carbon-fiber-reinforced plastic (CFRP) and aluminum alloy subjected to quasi-static tensile loading. The 2D digital image correlation technique was used to record the deformation and strain of the overlap area. The results show that the thickness of the adhesive layer had a negative effect on the mechanical properties of the hybrid joints, and when the thickness of the adhesive layer was increased from 0.2 to 0.8 mm, the peak load and the energy absorption (EA) values of the hybrid joints were reduced by 14.38 and 23.22%, respectively. Compared with the bonded and riveted joints, hybrid joints showed better performances in peak load and EA values, and rivets were able to continue carrying loads when the adhesive layer failed. The typical failure modes of the hybrid joints included CFRP compressive failure, adhesive failure, fiber-tear failure, and light-fiber-tear failure. It was further found that the adhesive could disperse the stress around the rivet holes and effectively reduce the stress concentration around the rivet holes.

Effect of laser texturing and thermomechanical joining parameters on bond strength of steel-flax fiber reinforced vitrimer composites

The study examines laser texturing's impact on metal-composite hybrid joint mechanics formed via heat compression. It focuses on sustainable composite fabrication, utilizing flax fibers and a recyclable vitrimer resin known for dynamic covalent bond exchange capabilities, enhancing recyclability, repairability, and reshaping. Simulated heating conditions determined optimal bonding between the composite and laser-textured surfaces, considering the glass transition temperature for minimum temperature and time requirements. Deviations from initial heat pressing conditions (135 °C, 0.6 MPa, 5 min) reduced bonding strength, underscoring parameter sensitivity. Cross-tensional tests under varied laser texturing conditions, supported by microscopic examinations, revealed optimal strength (1680 N) with a 150 μm hatch distance and 9 repetitions, ensuring consistent ablation volume and time. Supplementary ANSYS simulations pinpointed stress concentration regions in cross-tensional joints, guiding adjustments in laser texturing within the region of interest to assess mechanical properties. The hybrid cross-tensional and lap shear joints were also reconnected after each fracture via heat compression, allowing for the evaluation of degradation in bonding strength over each cycle.

Fatigue design of stress relief grooves to prevent weld root fatigue in butt-welded cast steel to ultra-high-strength steel joints

In the welded joints, fatigue failures typically originate from defects or notch-like geometries under cyclic loading. This study investigates the impact of stress relief grooves (SRG) on the fatigue performance of butt-welded cast steel to ultra-high-strength steel components using experimental fatigue tests and finite element method. The experiments examined the fatigue properties of hybrid joints between G26CrMo4 cast steel (t = 20 mm) and S960 steel plate (t = 6 mm) with and without SRG. Gas metal arc welding process was used to weld the butt joints that had a permanent root backing machined on the cast steel part, causing a crack-like defect to the weld root. Additionally, the top surfaces of the welded parts were aligned, resulting in a significant axial misalignment in the butt joint. The SRG, positioned close to the weld root, was found to have a beneficial influence on the joint’s fatigue performance by a factor of 1.2 when using the nominal stress criterion. However, the fatigue capacity was still roughly 35% lower compared to the symmetrical equivalent due to the secondary bending stress, caused by axial misalignment. The finite element analyses indicated that the SRG reduces the amount of secondary stresses at the weld root leading to lower total structural stress. The study recommends using the FAT80 (m = 3) design curve in the structural stress method, for similar butt-welds having a crack-like defect, parallel to the loading direction, at the weld root. However, for welded joints with crack-like defects, it is advisable to use linear elastic fracture mechanics rather than relying solely on stress-based local approaches.

Evaluation of shear performance of timber-timber composite joints

The mechanical performance of timber composite floors is influenced by the degree of composite action between the components. In this study, the shear strength performance of cross-laminated timber and glued laminated timber composite floors based on the joining method was evaluated by push-out test. Eight types of timber-timber composite joints were evaluated using three different methods: lag screw joints, glued-in rod joints using fully threaded bolts and glass fiber reinforced plastic, and hybrid joints. Strength characteristics were derived to make theoretical predictions on the load-carrying capacity of the joints. The results showed that the glued-in rod joints were superior to the lag screw joints, with slip coefficients and ductility measured as 10 times and 2.5 times higher, respectively. The reliability of the strength characteristics of the glued-in rod joints was remarkably different depending on the presence or absence of anti-adhesive tape applied to the timber-to-timber joint surface. The load capacity of the hybrid joint, which combines mechanical and glued-in rod joining methods, was 47% higher than that of the lag screw joint and 38% higher than that of the glued-in bolt joint. In the European Yield Model modified to estimate the load capacity of joints, the rope effect and the yield moment of the fasteners had a remarkable impact on the predicted load capacity.

Experimental Investigation and Numerical Simulation of Bonded, Bolted, and Hybrid Joints in CFRP Laminates Under Tensile Loading

Experimental Investigation and Numerical Simulation of Bonded, Bolted, and Hybrid Joints in CFRP Laminates Under Tensile Loading

Failure analysis of thermoplastic composites subject to galvanic corrosion in hybrid metal–composite joints

The damage sustained by carbon fibre reinforced polymers due to the effect of galvanic corrosion induced by coupling between carbon fibres and a metallic material in a hybrid joint is investigated. Composite laminates with two fibre architectures and two thermoplastic matrices (polycarbonate and polyamide 6) are coupled to a metallic fastener and exposed to salted fog conditions. Both the effects of the salted fog environment and the coupled effect of the environmental and the galvanic corrosion are analysed. The analysis is centred in, firstly, characterising the functional properties of the hybrid joint, secondly characterising the laminate properties and finally characterising the chemical degradation of the matrix. The results show a degradation of properties for the polycarbonate material, in terms of bearing performance and interlaminar shear strength as well as presenting obvious changes in the thermal characterisation. The polyamide composites remain largely unaffected and only minor changes in the surface appearance are noteworthy.

Adhesive Snap-Fit Joints for Modular Wind Turbine Blades: A Numerical Feasibility Study

Larger rotor diameters are sought by wind turbine manufacturers as they favour cost-effective energy generation. However, manufacturing, transporting, and installing longer blades gets increasingly complicated, time-consuming, and costly. While a potential solution lies in spanwise segmentation, available modular blade technologies are still relatively immature, have drawbacks, and are yet to be used for blades exceeding 80 meters. A key challenge to blade segmentation is the addition of joints, which can result in both structural as well as aeroelastic penalties, when comparing segmented designs to their monolithic counterparts. To tackle these issues, in this study, we present the proof of concept and initial feasibility of an adhesively bonded snap-fit joint. The study assesses the joint’s load carrying capacity under quasi-static loading conditions at two levels: first, at the component level, focusing on the snap-fit elements, and second, at the system level, examining the integration of these components into the blade section. Under the specified assumptions, the results highlight the hybrid joint’s capability to withstand substantial loads of the order of magnitude required to meet operating requirements.

Failure mechanisms in pre-tensioned bonded hybrid joints

ABSTRACT This study investigated the failure mode of pre-tensioned bonded hybrid joints in steel structures using Digital Image Correlation (DIC) alongside Finite Element Analysis (FEA) and compared the results with those of adhesive bonded joints of identical geometry. While all joint types initially exhibited ideal adhesive joint behaviour at low loading levels, with linear elastic response, differences emerged as loading increased. In particular, hybrid joints exhibited out-of-plane deformations near the ends of the splice plates, a feature not observed in bonded joints. Shear deformations consistently peaked at the ends of the overlap for all joint types and increased with increasing load levels. In contrast to bonded joints, hybrid joints demonstrated resilience under escalating loads, maintaining resistance due to the presence of bolts despite the increased deformations. This study contributes to the understanding of the observed failure mode: while hybrid joints initially resembled ideal bonded joints at lower loads, increasing loads caused critical cracks to initiate at the overlap ends in the adhesive layer, culminating in bonded joint failure. In conclusion, this study has elucidated the failure mode of hybrid joints, providing insights for modelling and dimensioning in steel structures.

The Seismic Performance of Self-Centering Ribbed Floor Flat-Beam Frame Joints

To achieve rapid post-earthquake repair of self-centering ribbed floor flat-beam frame structures, a ductile hybrid joint consisting of dog-bone-shaped, weakened, energy-dissipating steel bars connected to the upper and lower column sections through high-strength threads is proposed based on the damage control design concept. By moving the ductile energy-dissipating zone out to the locally weakened section of the energy-dissipating steel bars and the locally unbonded prestressed steel bars in the core area, the residual deformation was limited and the seismic performance improved. Based on the working principle of hybrid joints, low cycle loading tests were conducted on two joint specimens to analyze the influence of lateral prestress on the seismic performance of the hybrid joints. Numerical modeling methods were used to compare the position of the energy-dissipating steel bars in the composite layer and the friction performance of the joints. The research results indicated that the hybrid joint had stable load bearing, deformation, and energy dissipation capabilities, with damage being primarily concentrated in the energy-dissipating steel bars. Even at an inter-story displacement angle of 5.5%, the upper and lower column segments remained elastic. After unloading, the connection seam at the joint was closed, and the self-centering performance was good. When the inter-story displacement angle reached 5.5%, the lateral prestress increased from 150 kN to 250 kN, the ultimate bearing capacity of the joint increased by 16.3%, and the cumulative energy consumption increased by 30.0%. The influence of the friction coefficient of the joint surface on the structural performance was set at a threshold of 0.7. When it was less than the threshold, the ultimate bearing capacity and initial stiffness of the joint increased with the increase in the friction coefficient. After reaching the threshold, the increase in the ultimate bearing capacity of the joint slowed down, and the rate of stiffness degradation gradually accelerated. This joint showed excellent seismic performance and can thus achieve post-earthquake repair of structures.

Effect of anodizing pretreatment on laser joining stainless steel to CFRTP

Metal-carbon fiber reinforced thermoplastic (CFRTP) hybrid joints have demonstrated its effectiveness in achieving lightweight design concept in engineering application. However, it is difficult to produce high-reliability joint due to differences in physical as well as chemical properties between metal and CFRTP. In this study, porous oxide film was prepared by anodizing treatments with various anodic oxidation times on steel surface to enhance joint performance of laser-welded steel/CFRTP. The maximum steel/CFRTP joint fracture load of 1960 N was reached, which was three times as much as that obtained with pretreated steel. The results indicated that porous structure was introduced into steel surface by anodization process, which resulted in better wettability of molten CFRTP and higher surface roughness, thus contributing to the enhancement of joint area as well as mechanical interlocking at the interface, further improving joint performance. Meanwhile, more Cr-O-C chemical bonds were produced because Cr-rich oxide film formed after anodizing contributed to interfacial chemical reaction. The chemical bond between oxide film and CFRTP was proved through density functional theory (DFT) calculation. Additionally, with the increase of anodic oxidation time, chemical bond content and surface roughness first enhanced and then reduced, which suggested that the porous structure prepared with 20 min anodizing time could best improve the interfacial mechanical interlocking, and promote the chemical bonding as well as steel/CFRTP joint interfacial bonding.

Effect of Compressive Stress on Copper Bonding Quality and Bonding Mechanisms in Advanced Packaging.

The thermal expansion behavior of Cu plays a critical role in the bonding mechanism of Cu/SiO2 hybrid joints. In this study, artificial voids, which were observed to evolve using a focused ion beam, were introduced at the bonded interfaces to investigate the influence of compressive stress on bonding quality and mechanisms at elevated temperatures of 250 °C and 300 °C. The evolution of interfacial voids serves as a key indicator for assessing bonding quality. We quantified the bonding fraction and void fraction to characterize the bonding interface and found a notable increase in the bonding fraction and a corresponding decrease in the void fraction with increasing compressive stress levels. This is primarily attributed to the Cu film exhibiting greater creep/elastic deformation under higher compressive stress conditions. Furthermore, these experimental findings are supported by the surface diffusion creep model. Therefore, our study confirms that compressive stress affects the Cu-Cu bonding interface, emphasizing the need to consider the depth of Cu joints during process design.