Bond Joint Research Articles

Bond Behavior of CFRP–Concrete Bonded Joints with Additional GFRP Layer: Effect of Bonding Sequence

Existing studies have shown that bonding a ±45° biaxial GFRP under CFRP laminate can significantly improve the load-carrying capacity and ultimate deformation of CFRP–concrete bonded joints. In such a bonding configuration, the GFRP interlayer is wider than the CFRP laminate so that the interfacial stress can be redistributed to achieve a higher fracture work; however, the effect of the bonding sequence,—specifically, the position of the GFRP layer—on the bond behavior is not yet clear. In this study, considering the same CFRP and GFRP usage, three types of CFRP–concrete bonded joints with CFRP bonded under, above, and between GFRP layers were prepared and tested under single-shear loading. Digital image correlation (DIC) was used to measure the deformation of the bonded joints during the test. Afterward, the failure mode, load–displacement behavior, and principal strain distribution were analyzed. The experimental results show that the dominant failure mode is the combined cohesion failure mode within the concrete and GFRP delamination, which is not affected by the bonding sequence. Compared to conventional CFRP–concrete bonded joints, bonding the CFRP laminate above, under, and between the GFRP layers achieved a 157.6%, 175.0%, and 177.2% increase in load-carrying capacity, respectively. Accordingly, the ultimate deformation also recorded an 83.0%, 103.6%, and 86.3% increase. However, the bonding sequence showed a slight influence on the initial stiffness of the load–displacement curve with a maximum difference of 16.1%, taking the minimum as a reference, which could be attributed to the differences in the strength and stiffness between the CFRP–concrete and CFRP–GFRP–concrete interfaces.

Advances in Adhesive Bonded Joints for Composite Materials: A Comprehensive Review

Adhesive bonded joints have become increasingly significant across various high-tech industries, including aerospace, automotive, marine, and construction. This growing importance is largely due to their efficiency in joining lightweight composite materials, which are integral to modern engineering applications. In this review paper, we offer a comprehensive update on the latest advancements in adhesive bonded joints specifically for composite materials. The paper delves into several critical aspects of adhesive bonding, beginning with surface preparation. Proper surface preparation is crucial for achieving optimal bond strength and durability, and this paper explores the latest techniques and best practices in this area. It also examines current testing methods used to evaluate the performance of adhesive joints, ensuring that they meet stringent industry standards. Durability is another key focus of the review. We discuss various considerations related to the long-term performance of adhesive bonded joints, including environmental factors, load-bearing capacity, and resistance to aging and degradation. The paper also highlights recent innovations in adhesive technologies. These advancements include new formulations and types of adhesives that enhance bonding capabilities and overall joint performance. Additionally, we cover the latest developments in surface treatments, which play a critical role in improving adhesion by modifying the surface properties of composite materials. In summary, this review offers a thorough and up-to-date examination of adhesive bonded joints for composite materials, highlighting both recent advancements and ongoing challenges, while providing valuable insights into future research directions

Study on Parallel Bond and Smooth Joint Dual Model Parameter Calibration of Mechanical Properties of Shale Under Pressure

Study on Parallel Bond and Smooth Joint Dual Model Parameter Calibration of Mechanical Properties of Shale Under Pressure

Bond behavior of CFRP-strengthened steel structures and its environmental influence factors: a critical review

Adhesively bonded carbon fiber-reinforced polymer (CFRP) systems have shown great promise for strengthening damaged steel structures, offering potential enhancements in the longevity of steel structures. However, the degradation of bond performance of CFRP under harsh environments remains a critical concern for researchers and engineers, as it may significantly impact the efficiency and durability of bonded CFRP strengthening systems. This paper presents a comprehensive review of the impact of key characteristics of bonded joints, such as the CFRP modulus, adhesive performance, bond length, adhesive layer thickness, and bond joint geometry, on the bonding performance of CFRP strengthening systems. Additionally, the influences of environmental factors, including elevated and sub-zero temperatures, moisture, corrosion, humidity, wet-dry cycles, ultraviolet radiation, and freeze-thaw cycles on the bond behavior, were also reviewed. By synthesizing and analyzing existing research insights into the effects of reinforcement materials, bond joint design parameters, and environmental factors on bonding performance, this review article attempts to enhance practitioners' understanding of bond behavior in this field and also provides guidance for future research.

Multi-scale investigation on mechanical properties of wood joints bonded with a polyurethane adhesive in successive cycles of accelerated aging treatments

To gain a deeper understanding of the bond durability in adhesively bonded wood products, a multiscale investigation of the mechanical properties of wood joints bonded with a one-component polyurethane (PU) adhesive in successive cycles of accelerated aging treatment was conducted by combining nanoindentation (NI) and conventional tensile-shear techniques. The delamination ratio, shear strength, and wood failure ratio of the wood joints, as well as the reduced elasticity modulus (Er) and hardness (H) of the PU resin, cell walls in the interphase region (CW–I), and control cell walls (CW) were evaluated. The correlations between the macro shear strength and micromechanical properties were further established. The results showed that the average delamination ratios of the wood joints were 10%–26 % after eight cycles of hydrothermal treatment. Macromechanical and most micromechanical properties substantially decreased with an increase in the number of treatment cycles, with maximum reductions of 37 %, 24 %, 60 %, 56 %, 48 %, and 57 % for the shear strength, wood failure ratio, Er of PU, H of PU, Er of CW-I, and Er of CW, respectively. The linear regression for the mechanical properties and the number of treatment cycles indicated that the Er of PU, CW-I, and CW, as well as the H of PU, showed linear downward trends (with R2 values of 0.765–0.921) during successive aging treatments. Significant and positive linear correlations were found between the shear strength and micromechanical properties of PU, with correlation coefficients of 0.970 (P < 0.01) and 0.941 (P < 0.05) for Er and H of PU, respectively. The wood failure ratio showed significant positive correlations with the Er values of CW-I (P < 0.01) and CW (P < 0.05), whereas the proportion of wood failure in the interphase was significantly (P < 0.05) negatively correlated with the Er value of CW. The shear strength was positively correlated with the Er of the cell walls, with correlation coefficients of 0.861 and 0.868 for CW-I and CW, respectively. In summary, both the micromechanical properties of the PU resin and the elasticity of the wood cell walls in the wood-adhesive interphase were demonstrated to be key factors affecting the bond durability of wood bond joints.

Effect of Mechanical Fastening Versus Adhesively Bonded Joints of Polymer Composites on Lap Joint Strength

To examine the viability of combining pine needle fiber-reinforced polylactic acid composites, galvanized iron sheet and aluminum sheet via the use of mechanical fastening and adhesive bonding methods was investigated. The study included the preparation of three distinct kinds of joints, namely, adhesive, nut-bolt, and rivet joints, with the purpose of assessing their tensile and flexural strength. The findings indicated that the use of both mechanical fastening and adhesive bonding methods yielded successful outcomes in the bonding of these materials, with the strength of the joints changing based on the approach employed. The adhesive bonding approach exhibited superior tensile and flexural strength in comparison to the mechanical fastening technique. The microstructural examination demonstrated that the adhesive bonding approach yielded a consistent and uninterrupted contact between the materials, while the mechanical fastening technique exhibited some surface imperfections and deformations. The results indicated that both approaches were effective in producing robust and long-lasting joints.

Experimental study of bonded, bolted, and hybrid bonded-bolted single lap shear joints with woven CFRP adherends

This paper presents an extensive experimental performance study of bonded joints (BJs), only bolted joints (OBJs) and hybrid bonded-bolted joints (HJs). For each joint type, three test configurations are considered: namely, short, medium and long overlap lengths. In each case, the adherends comprise quasi-isotropic twill woven CFRP. For each joint type/overlap length combination, three specimens are tested for statistical representation. HJs demonstrate 1.4, 1.5 and 1.5 times higher failure load and 1.5, 1.6 and 1.9 times higher stiffness than OBJs, for short, medium and long overlap, respectively. In all test cases, HJs outperform BJs except for short overlaps where BJs outperform both HJs and OBJs. OBJs perform poorly in terms of failure load and Hooke’s stiffness. Nevertheless, due to bearing deformation at bolt hole locations, OBJs experience higher failure displacements than BJs and HJs leading to a desirable energy absorption mechanism compared to HJs and BJs. This is thanks to the bearing failure mode of the joint despite much lower failure load in OBJs. It was found that increasing the overlap length generally benefits BJs. However, for medium length overlap specifically, HJs show better performance than BJs. Stress–strain behaviours show a linear behaviour for all test groups with significant joint rotation for OBJs compared to BJs and HJs. Failure mechanism studies presented in the paper show that BJs fail in cohesive failure mode for all test groups. OBJs fail in bearing mode, which is followed by net tension failure. OBJs experience matrix cracking and delamination at bolt hole locations. On the contrary, HJs experience considerably less bearing failure at bolt holes due to the load bearing contribution from the adhesive.

Design of Adhesive Bonded Joints

Adhesive bonded joints have become vital to modern engineering, offering advantages such as weight reduction, enhanced fatigue performance, and improved stress distribution [...]

Multidimensional Evolution and Driving Factors of Securities Firms’ Collaborative Bond Joint Underwriting Networks in China: A Comprehensive Analysis from 2011 to 2020

This study utilizes the joint bond joint underwriting data of China’s securities firms from 2011 to 2020 to systematically explore the evolutionary characteristics of China’s collaborative bond joint underwriting networks from temporal, topological, and spatial dimensions. By employing social network analysis, Ucinet, and ArcGIS, we construct a longitudinal network panel data to quantitatively analyze the driving factors and their underlying mechanisms. The findings reveal that, in terms of topological structure, China’s bond joint underwriting networks exhibit increasingly mature, active, balanced, and accessible features, with domestic securities firms such as China Securities Co., Ltd. emerging as the backbone and foreign-backed firms gradually fading. In the spatial dimension, urban collaboration presents a transformation from triangular to butterfly-shaped, quadrilateral, and ultimately multicore networks. At the regional scale, inter-regional collaboration is most extensive between the eastern regions, followed by eastern–central regions, with eastern–western and central–western regions relatively less engaged. At the urban scale, the central positions of Beijing, Shenzhen, and Shanghai are gradually strengthening, and their external radiation scope is expanding annually. The underlying mechanism driving this evolution is the increasing opportunities for securities firms to establish and adjust their cooperative relationships due to the maturing and active bond joint underwriting networks in China. To compensate for the opportunity cost of bond joint underwriting and to maximize collaboration benefits, securities firms need to select potential partners with close geographical proximity, similar business domains, larger underwriting scales, “friends of friends,” and “network star” status, thereby promoting the continuous evolution of China’s bond joint underwriting syndicates.

Evaluation of XD 10 Polyamide Electrospun Nanofibers to Improve Mode I Fracture Toughness for Epoxy Adhesive Film Bonded Joints

The demand for ever-lighter structures raises the interest in bonding as a joining method, especially for materials that are difficult to join with traditional welding and bolting techniques. Structural adhesives, however, are susceptible to defects, but can be toughened in several ways: by changing their chemical composition or by adding fillers, even of nanometric size. Nanomaterials have a high surface area and limited structural defects, which can enhance the mechanical properties of adhesives depending on their nature, quantity, size, and interfacial adhesion. This work analyzes the Mode I fracture toughness of joints bonded with METLBOND® 1515-4M epoxy film and XantuLayr electrospun XD 10 polyamide nanofibers. Two joint configurations were studied, which differed according to the position of the nanomat within the adhesive layer: one had the nanofibers at the substrate/adhesive interfaces, and the other had the nanofibers in the center of the adhesive layer. Double cantilever beam joints were manufactured to evaluate the Mode I fracture toughness of the bonding with and without nano-reinforcement. The nanofibers applied at the substrate/adhesive interface improved the Mode-I fracture toughness by 32%, reaching the value of 0.55 N/mm. SEM images confirm the positive contribution of the nanofibers, which appear stretched and pulled out from the matrix. No fracture toughness variation was detected in the joints with the nanofibers placed in the middle of the adhesive layer.

Numerical Modelling and Experimental Testing on Polyurethane Adhesively Bonded Joints Behaviour in Wood-Wood and Wood-Carbon Fibre Reinforced Polymer Layouts

Numerical Modelling and Experimental Testing on Polyurethane Adhesively Bonded Joints Behaviour in Wood-Wood and Wood-Carbon Fibre Reinforced Polymer Layouts

Microstructural characterization of Ti/Cu/Ti diffusion bonded system through a micromechanical data-driven neural network approach

In this work, a micromechanical data-driven neural network approach, named as adjacent gradient neural network (AGNN), was developed to characterize the microstructural features of Ti/Cu/Ti Diffusion Bonded joints with a wide range of interlayer thicknesses. The AGNN model facilitates the evaluation of microstructure on the basis of Young’s modulus and hardness distributions in the joint zone. The results indicated that the AGNN model accurately classified the microstructural constituents including the stabilized eutectoid structure and the intermetallic compounds; however, there existed some deviations at high-hardness regions, which was originated from the low penetration depth in the indenting process. The predictive outcomes also quantitatively revealed that the increase in the interlayer thickness was accompanied with the generation of intermetallic compounds; however, the proportion of eutectoid structure decreased in the joint zone. In summary, the outcomes of this work indicate that it is feasible to predict the microstructural features of a Ti/Cu/Ti diffusion bonded joint with a preferred interlayer thickness and establish a meaningful correlation between the micromechanical properties and the morphological characteristics.

Effects of Different Coatings, Primers, and Additives on Corrosion of Steel Rebars

In this research, methods of increasing the corrosion resistance of reinforced concrete were experimentally investigated. The study used silica fume and fly ash at optimized percentages of 10 and 25% by cement weight, polypropylene fibers at a ratio of 2.5% by volume of concrete, and a commercial corrosion inhibitor, 2-dimethylaminoethanol (Ferrogard 901), at 3% by cement weight. The corrosion resistance of three types of reinforcements, mild steel (STt37), AISI 304 stainless steel, and AISI 316 stainless steel, was investigated. The effects of various coatings, including hot-dip galvanizing, alkyd-based primer, zinc-rich epoxy primer, alkyd top coating, polyamide epoxy top coating, polyamide epoxy primer, polyurethane coatings, a double layer of alkyd primer and alkyd top coating, and a double layer of epoxy primer and alkyd top coating, were evaluated on the reinforcement surface. The corrosion rate of the reinforced concrete was determined through results of accelerated corrosion and pullout tests of steel-concrete bond joints and stereographic microscope images. The samples containing pozzolanic materials, the corrosion inhibitor, and a combination of the two showed significant improvement in corrosion resistance by 7.0, 11.4, and 11.9 times, respectively, compared to the control samples. The corrosion rate of mild steel, AISI 304, and AISI 316 decreased by 1.4, 2.4, and 2.9 times, respectively, compared to the control sample; however, the presence of polypropylene fibers reduced the corrosion resistance by 2.4 times compared to the control.

Fatigue and Tensile Behaviors of High Stiffness Adhesive Bonded and Hybrid Joints with Composite-Steel Dissimilar Materials

Fatigue and Tensile Behaviors of High Stiffness Adhesive Bonded and Hybrid Joints with Composite-Steel Dissimilar Materials

Polyimide Films Manufactured Using Partially Wet Electrospray Deposition

In electrospray deposition (ESD), solute material is dispersed in a carrier solvent and atomized into a cloud of microdroplets under the influence of a strong electric potential. The volatility, ESD parameters, and environmental conditions determine the rate of solvent evaporation. Complete in-flight solvent evaporation produces dry particles of material that are deposited on the target. In contrast, when the evaporation is incomplete, some residual solvent is delivered with the material. We define these regimes as dry (complete evaporation) and partially wet (incomplete evaporation) ESD. Here, we compare the microstructure and functional characteristics of films deposited in both regimes. We selected polyimide as our solute material given its importance in electronic, health, and environmental applications. An electrospray printhead that provides a tunable solvent evaporation rate via co-flowing air is used to deploy the polyimide. The dry and partially wet regimes can be selected by altering the solution flow rate and the air co-flow rate. Particulate films are formed when the polyimide is delivered to the target dry (solvent-free). When solvent is delivered with the polyimide, a dense (partially wet) film is formed on the target. A numerical model of droplet evaporation was developed, which shows the dominant effects of solution flow rate and freestream vapor concentration on the ESD regime. The dry and partially wet films were compared for various functional characteristics including dielectric strength, optical characteristics, and corrosion resistance. For most metrics, the partially wet ESD films outperformed the dry ESD films. Compared to the dry ESD films, the partially wet films had far greater dielectric strength (up to 340 V/μm) and higher optical transparency. Both ESD regimes provided comparable corrosion resistance, which enhanced the reliability of metallic bond joints in an electronics package.

Design and Development of a Repetitive Bending Tester for Bending Deformation in Textile Fabrics and Bonded Joints

Abstract It is critical to investigate the technical performance of non-stitch joining methods that have become prevalent recently. While examining the bonding strength and the factors that affect the strength of adhesive bonding in textiles, a bending test device was designed and produced to investigate the repetitive bending deformation. The novel test device provides bending deformation and tensile stress to the fabrics at different angles with its oscillating motion. The effects of repetitive bending deformation on fabric strength and adhesive bonding strength were investigated. The experimental analysis showed that repetitive bending deformation did not have a significant effect on the tensile strength of cotton/polyester blend and cotton fabrics. However, strength loss was observed in polyester fabric and cotton/elastane blended fabric samples. Moreover, significant reductions in bonded textile joint strength were observed even in the case of much less repetitive bending exposure.

SOLID STATE DIFFUSION BONDING OF X70 STEEL TO DUPLEX STAINLESS STEEL

This paper deals with the solid state diffusion bonding of X70 steel to duplex stainless steel. Microstructure and mechanical properties of the welded dissimilar steels were investigated. Optical microscopy, Electron Backscatter Diffraction, energy dispersive spectrometry, Vickers hardness measurements, and X-Ray Diffraction were the main techniques of characterization. Microtructural variation was observed in the X70 steel side compared to duplex stainless steel. The diffusion coefficient of iron, chromium, and nickel across the interface X70 steel/duplex stainless steel was also measured. The diffusion coefficient of iron and chromium is higher than that of nickel. The Vickers microhardness profile across the bond joint showed an abrupt decrease in hardness from duplex stainless steel to X70 steel. In addition, a dynamic recrystallisation reaction was observed close to the interface in the X70 steel side.

Effect of Adhesive Layer Thickness and Slant Angle on Piezoelectric Bonded Joints

Piezoelectric materials have found their parts in numerous manufacturing applications such as transducers and sensors. Piezoelectric material shows anisotropy; in addition, its elastic field and electric field are integrated. The analysis of piezoelectric materials has obtained great interest among researchers with the development of smart structures. It is significant to explain the distribution of stress and electric displacement fields along the bonded edge. It has never been obvious how stress singularity and electric displacement fields are distributed at the vertex of piezoelectric dissimilar material joints. Stress and electric displacement distribution near the vertex along the interface of piezoelectric boned joints are investigated in this present research. Numerical analysis of piezoelectric dissimilar material joints is carried out by using Abaqus FEA software. From the numerical analysis, it is observed that stress, displacement, electric potential, electric displacement field evolvement along the interface edge rises with the increment of adhesive layer thickness and slant angle. So, a thin adhesive layer thickness and small slant angle are more reliable for operation.

Effect of interlayer adherend inclusions on strength of composite bonded joints

Foreign objects such as backing tapes may get embedded between the plies of a laminated polymer composite during its fabrication which can compromise the composite panel or the adjacent bond joint. This paper investigates the effect of such inter-layer inclusion defects in laminated carbon fiber composite adherends, on the strength of an adjacent single lap bonded joints, using both experimental and computational methods. Composite laminates composed of 0° unidirectional lamina were fabricated with Polytetrafluoroethylene (PTFE) strips embedded between the first two plies closest to the bond line. Three different inclusion positions were investigated and the location of the inclusion defect yielding the lowest strength was identified. The inclusion location in the most compromised joint was then used to study the effect of this type of defect in adherends having different ply orientations. Finite Element (FE) stress analysis was performed to understand the variation in the shear and peel stresses due to the presence of the inclusion. FE analysis revealed higher shear and peel stresses in bonded joints adjacent to inclusion defects.

Influence of Laser Treatment on End Notched Flexure Bonded Joints in Carbon Fiber Reinforced Polymer: Experimental and Numerical Results.

Surface pretreatment for bonding is one of the most important steps for the manufacturing of a reliable bonded joint. In this paper, the effectiveness of an innovative pretreatment by CO2 pulsed laser for bonding Carbon Fiber Reinforced Polymer (CFRP) was investigated. End Notched Flexure (ENF) specimens were made with different densities of laser treatment, and the respective fracture toughness was obtained through the Compliance-Based Beam Method (CBBM). Furthermore, a cohesive model for simulating debonding processes was illustrated, and the cohesive parameters were obtained by an inverse method. The achieved results represent a fundamental step for the development of a numerical model useful for the determination of laser texturing as a function of the applied local stress into the bonded joint.