Adhesive Joints Research Articles

Estimation of relevant shear properties of adhesive joints through analytical modeling of experimental torsion tests

ABSTRACT The paper investigates the response of different adhesives joints under torsional loading. The stiffness and strength characteristics of the adhesives joints are estimated by fitting adaptable piecewise linear models with the experimental results of torsion tests. Efficient fitting techniques are adopted to estimate model parameters and effectively quantify relevant shear properties of the adhesive joints under test. The proposed experimental-analytical procedure represents a valid alternative to the conventional bending and shear tests reported in the literature: with respect to the bending tests, the torsion test yields more accurate results because it induces a pure shear stress rather than a complex bending-shear stress state; the torsion test is also easier to be performed with respect to the shear test, which requires testing fixtures that may locally affect the experimental results.

Optimization of Adhesive Joint Design in Timber–Glass Systems: Enhancing Structural Performance with Primer Treatment

The increasing use of large glass surfaces in modern architecture requires robust adhesive solutions that balance aesthetic appeal with structural resilience, particularly in timber–glass applications. This study examines the influence of primer treatments on the shear performance of timber–glass adhesive joints, employing a combination of experimental testing and simulation techniques. Double-lap shear tests with epoxy adhesives assess the impact of various surface treatments on joint stiffness, shear stress distribution, and deformation. Additionally, a finite element model is developed to simulate joint behavior, evaluate failure modes, and analyze displacement patterns. Results indicate that primer applications notably enhance structural integrity by reducing displacement and increasing joint stability, thereby supporting more durable timber–glass assemblies. These findings offer valuable insights for advancing adhesive technologies in architectural components, enabling a closer alignment between structural performance and design innovation in timber–glass systems.

Investigating Multi-Material Additive Manufacturing for Disassembly and Reparability of Adhesive Joints by Precision Heating

Additive manufacturing enables new design solutions across various engineering fields. This work presents a method to enhance the sustainability of adhesive joints by designing joints that can be disassembled and repaired multiple times. The approach involves the use of a Multi-Material Additive Manufacturing process to produce substrates with integrated circuits and electrical resistance, printed using a conductive filament. This resistance can be used to heat the thermoplastic adhesive layer up to 110 °C, allowing for reversibility in the assembly process and enabling joint re-use and repair without constraints on the component’s materials and thicknesses. The joints tested after successive assembly/disassembly operations reach maximum strength during the first iteration, which decreases by around 50% after five repair iterations. The focus of the work is on the feasibility of this process, but it is expected that performance can be improved after process optimization. This result could be highly valuable for enabling component in-service healing and the design for demanufacturing and remanufacturing.

Predicting natural aging effects on fatigue life of CFRP–aluminum adhesive joints using machine learning and accelerated aging data

This study investigates the behavior and reliability of CFRP-to-aluminum adhesive joints subjected to hygrothermal conditions under both natural and accelerated aging scenarios. Natural aging durations ranged from 1 to 3 years, while accelerated aging was performed over periods of 100–1200 h in 50-hour intervals. Fatigue life was evaluated using a three-point bending test, revealing a significant degradation in joint performance due to hygrothermal exposure. Key findings include a 25.98% reduction in fatigue life for samples naturally aged for three years and a comparable 27.33% reduction in samples subjected to 1000 h of accelerated aging. Hygrothermal conditions caused notable matrix degradation, transitioning failure modes from cohesive to mixed types (cohesive, adhesive, and fiber tear failures), with a direct impact on joint durability. Machine learning models, including artificial neural network (ANN), support vector regression (SVR), linear regression, polynomial regression, and random forest regression, were employed to predict natural aging durations based on accelerated aging data. Among these, the random forest regressor exhibited the highest predictive accuracy, effectively correlating accelerated aging durations to natural aging conditions. This study provides critical insights into the failure mechanisms and long-term performance of adhesive joints, offering a novel predictive approach to estimate natural aging effects from accelerated tests. These findings highlight the potential for optimizing joint designs to enhance durability and reduce failure risks in operational environments.

Experimental study on mode I fracture response of adhesive joints subjected to systematic creep damage

Experimental study on mode I fracture response of adhesive joints subjected to systematic creep damage

Distributed Backface Strain Sensing of Composite Adhesively Bonded Joints under Mode II Fatigue Loading

Distributed Backface Strain Sensing of Composite Adhesively Bonded Joints under Mode II Fatigue Loading

3D-printed single-lap adhesive joints made of functionally graded adherents: experimental and numerical study

ABSTRACT This study investigates the fabrication and performance of single-lap adhesive joints made from functionally graded materials using Fused Deposition Modeling. Functionally graded materials, with their continuous variation in material properties, offer a solution to the common issue of interfacial cracking in composite materials by eliminating discrete interfaces. The adherents used in this study transition gradually between Polylactic Acid and Acrylonitrile Butadiene Styrene, providing enhanced mechanical performance. Five different single-lap joint configurations were tested under tensile loading to evaluate the effect of the graded adherents on joint strength. The experimental results indicate that incorporating Acrylonitrile Butadiene Styrene into Polylactic Acid-based adherents significantly improves both joint strength and ductility. For instance, graded adherents with Acrylonitrile Butadiene Styrene sides adhered together exhibited a 41% greater extension compared to joints made of pure Polylactic Acid adherents. Additionally, the failure mode shifted from adhesive failure in pure material joints to adherent failure in graded joints, demonstrating improved adhesion properties. The findings were further supported by Finite Element analysis, which showed good agreement with the experimental data. The stress distribution analysis revealed effective management of stress concentrations within the graded structures, reducing the likelihood of failure and enhancing joint durability. This research underscores the potential of functionally graded additive manufacturing in optimizing the design and performance of adhesive joints.

The effect of dynamic shock load on the adhesion strength of fiber reinforced composite plates

Abstract In order to optimize the best possible combination, three input variants that influence adhesion properties were chosen for this investigation. The adhesives, fillers used to blend with the adhesives, and surface treatments were selected for this objective. This study has selected these input variants to compare the adhesion property between a thermoset composite and thermoplastic composite plate. The adhesion joint zone was subjected to dynamic impact shock loading, and the adhesion strength was analyzed both before and after the shock exposure. In order to determine the extents of the adhesion strength reduction subsequent to dynamic loading, the specimens’ were evaluated both prior to and subsequent to shock loading. Three distinct thermoset adhesives, including vinyl ester, epoxy, and polyester, are blended with ceramic particles, including silicon and hafnium carbide, are used to bond the composites. In a 1:50 ratio, the additives were incorporated into the adhesives. To assess shock pressure-induced damage, the specimens were characterized after experimentation. The shock exposure appears to have degraded the material extruded specimen’s surface, leaving the interface unmodified. The responses were found to be contingent upon the type of filler used during adhesive blending and the surface treatment. After 50 shocks, composite plates’ adhesion property decreased slightly but after 100 shocks, it decreased significantly. The study found that the composite plate adhesion dropped by 4.97% after 50 shocks. After 100 shocks, adhesion strength dropped 25.46%.

Surface treatment of carbon fiber reinforced polymer for adhesive bonding with pioneer epoxy using atmospheric pressure plasma jet

A recent technique used in surface preparation for adhesive bonding is plasma treatment. In the Philippines, one of the most accessible brands of adhesive is Pioneer epoxy adhesive and, currently, there has been no existing research on the effect of plasma treatment with this adhesive. Thus, this research aims to investigate the effects of plasma pretreatment on the adhesive bonding of carbon fiber-reinforced epoxy adherents with the Pioneer epoxy adhesive. To achieve this, carbon fiber-reinforced polymers (CFRPs) samples were first plasma treated using an atmospheric pressure plasma jet (APPJ) for 0, 1, 2, and 3 min. Then, these were used to form the joint systems with three different adherent combinations. The samples were characterized using the lap shear test, contact angle measurements, optical microscope, laser microscope, and Raman spectroscopy. The result shows that the surface free energy and roughness of the CFRP increase with increasing plasma treatment time. However, the roughness is contributed by the introduction of impurities, which can weaken the bonding. Thus, when the CFRP has adhered using Pioneer epoxy adhesive, the lap shear stress (LSS) of the treated CFRP proves to be lower than that of untreated samples, with a statistically significant p-value of 0.0069. From Tukey’s honestly significant difference (HSD) test, it is concluded that plasma treating the adherent weakens the adhesive bonding of the CFRP and Pioneer adhesive joint system instead of improving it. Potential explanations for this result include the introduction of impurities by the APPJ and the presence of Mercaptan polymer in the epoxy.

Experimental evaluation of residual tensile properties of CFRP‐aluminum butt adhesive joints subjected to systematic creep damage

AbstractThis study investigates the creep behavior and static mechanical response after creep of CFRP‐Aluminum adhesive joints subjected to sustained tensile loads. Initially, quasi‐static tensile tests were performed to determine the instantaneous static load (). Subsequently, creep tests were conducted at seven sustained load levels (i.e., 80%, 70%, 60%, 50%, 40%, 30%, and 20% of ) for durations ranging from 12 to 72 h. The main aim was to assess how creep affects the residual static mechanical properties of joints. Analysis of the creep curves revealed that the tested joints tolerated only 20%–50% of the creep load for the maximum specified creep duration (i.e., 72 h). Premature joint failure was observed under creep loads exceeding 50% of before reaching the maximum designated creep duration. Following this, tensile after creep (TAC) tests were performed on the creep‐loaded joints (i.e., those subjected to 20%–50% of ) at a crosshead speed of 0.5 mm/min. These tests aimed to determine the variations in the joint's residual mechanical properties. The TAC results indicated that the tensile stresses were primarily tolerated by the adhesive, with no significant delamination observed in the CFRP substrate. Notably, considerable reductions in residual properties (both strength and strain) were noted for longer creep durations, which were attributed to adhesive degradation. Conversely, reductions were minimal for shorter creep durations. Finally, semi‐empirical models were developed to predict the residual tensile properties of the joints for use in numerical simulations of creep behavior in future research.Highlights Examining creep and post‐creep tensile behavior in hybrid adhesive joints. Increased joint creep strain with higher creep load levels. Reduction in joint residual strength post‐creep. Creep causes reduced flexibility in the joint.

Improved Defect Sizing in Adhesive Joints Through Feature-Based Data Fusion

The current study focuses on the examination of adhesive-bonded materials, comprising different type of flaws like brass inclusions and delamination, through the application of ultrasound and X-ray non-destructive testing (NDT) techniques. The findings from both ultrasound and X-ray inspection were used to extract unique features, contributing to a more comprehensive understanding of the distinct characteristics demonstrated by each method. Several distinct features like absolute time of flight difference, peak-to-peak amplitude, variation coefficient in time and frequency domain, mean value of amplitude in frequency domain, and absolute energy were extracted from ultrasound testing results. Similarly, features like maximum amplitude, features from accelerated segment test, dilation, watershed segmentation, wiener deconvolution, and morphological gradient extracted from X-ray data underwent fusion. Different fusion techniques were applied to combine these features into a unified data set. A quantitative evaluation was performed for the individual features and their corresponding fused features from the ultrasound and X-ray results. A systematic analysis was conducted to quantify the improvement in defect sizing within the individual features and fused features from both the X-ray and ultrasonic investigations. The minimum absolute error of 0.02 mm was achieved with average fusion of absolute energy at 2nd interface and X-ray dilate features. This research not only delves into the diverse capabilities of ultrasonic and X-ray NDT methods in identifying flaws but also emphasizes the synergistic advantages arising from the integration of their distinct features. The qualitative study of defect estimation using the proposed fusion methods demonstrate that the distinctive fusion approaches significantly highlight the complimentary benefits of ultrasound and X-ray non-destructive testing methods, resulting in a quantifiable improvement in probability of defect detection.

Improvement adhesion durability of epoxy adhesive for steel/carbon fiber-reinforced polymer adhesive joint using imidazole-treated halloysite nanotube

Surface treatment is essential for enhancing adhesion durability and minimizing substrate damage in hybrid structural materials. This study focuses on developing a hybrid adhesive lap joint by incorporating halloysite nanotube (HNT) with imidazole-functionalized surfaces (IM-HNT) into epoxy adhesives to improve adhesion performance and thermal shock resistance. The surface treatment of HNT with imidazole (IM) introduced a curing catalyst effect, reducing activation energy by 50% and accelerating curing time by 90%, as confirmed by Kissinger’s plot and permittivity measurements. The optimized IM-HNT content improved thermal stability by controlling thermal expansion and enhanced mechanical properties, achieving a 15% increase in tensile strength and a 50% enhancement in fracture toughness. The adhesion performance of steel/carbon fiber-reinforced polymer (CFRP) hybrid joints was evaluated through single-lap shear tests, demonstrating a 25% improvement in shear strength. Adhesion durability was tested under cyclic thermal shock conditions, showing a 30% increase as IM-HNT content increased. Finite element analysis (FEA) revealed reduced residual stress at the adhesive interface, supporting the enhanced thermal and mechanical robustness. This study highlights the potential of surface-treated halloysite nanotubes in hybrid adhesive lap joints to significantly improve adhesion durability and thermal shock resistance, addressing critical requirements for hybrid structural materials.

Heterogeneous adhesive bonding between different CFRPs and Al 7075 after different surface treatments: A study on the selective practical applicability of the resin pre‐coating (RPC) technique

AbstractThis study suggested the judicious application of the resin pre‐coating (RPC) technique during adhesive bonding. Electrochemical surface treatment (ECST) and ultrasonic chemical treatment (UCT) were done on the Al 7075 alloy. Subsequently heterogeneous adhesive bonding of the ECST‐processed and the UCT‐processed alloy with three different CFRPs, namely unidirectional (UD) CFRP, 4‐Harness Satin‐weaved (4HSW) CFRP, and plain‐weaved (PW) CFRP was investigated. ECST and UCT processes resulted in trench‐type surface structures and cavitation pits, respectively. After ECST, contact angles of deionized water and diiodomethane reduced drastically. The highest strengths for the adhesive joints with UD, 4HSW, and PW CFRPs were 28.50, 30.40, and 26.85 MPa, achieved respectively after 10 V ECST without RPC, 1 M UCT without RPC and 1 M UCT with RPC technique. Thin layer cohesive failure at the alloy interface (TLCF‐AI) respectively increased and decreased after application of the RPC technique on the ECST‐processed and the UCT‐processed alloy surface. RPC technique after ECST decreased the single lap shear strengths, whereas this after UCT increased the single lap shear strengths of the heterogeneous adhesive joints with all considered CFRPs. The effectiveness of the RPC technique depended on the combinations of adherend surface morphologies and adhesive properties.Highlights Judicious application of RPC technique during adhesive bonding was suggested. ECST or UCT was done on Al 7075 before joining with UD, 4HSW, and PW CFRP. ECST and UCT respectively caused trench‐type structures and cavitation pits. RPC after ECST decreased adhesive joint strength and increased TLCF‐AI. RPC after UCT increased adhesive joint strength and decreased TLCF‐AI.

Bio-Microcapsules of Polybutylene Succinate (PBS) and Isocyanates: Towards Sustainable, Safer, and Efficient Adhesives.

This work describes the encapsulation of three different aliphatic isocyanates to reduce the risks associated with isocyanates' direct handling. The use of bio-based polybutylene succinate (bio-PBS) increases the sustainability factor as it allows for the use of microcapsules (MCs) from renewable sources with biodegradable features. The three different MCs (MCs-Monomer, MCs-Trimer, and MCs-Polymer) are spherical, crack-free, and matrix-type, containing an isocyanate payload between 67 wt% and 70 wt%. Protection against environmental moisture was improved, resulting in losses of less than 10% for most cases after one month. The bio-PBS MCs were found to be suitable as crosslinking agents in high-performance adhesive formulations for the footwear industry. Adhesive joints with encapsulated isocyanate exhibited peel strength values ranging from 3.28 to 4.56 N/mm, well above the minimum requirements for the intended footwear application. Additionally, these joints demonstrated improved creep resistance compared to those using non-encapsulated isocyanates. In this context, the MCs-Trimer stood out, providing exceptional thermal robustness to the joints, as they showed no failure or opening at 90 °C, consistent with commercial adhesives. These results confirm that bio-PBS MCs can be excellent components for future adhesive formulations and that matrix-type MCs can also be utilised for this purpose.

Detecting and assessing weak adhesion in structural single lap joints using a machine learning pipeline with lamb waves data

Detecting and assessing weak adhesion in structural single lap joints using a machine learning pipeline with lamb waves data

Experimental and Numerical Simulation Study on the Mechanical Properties of Integrated Sleeve Mortise and Tenon Steel–Wood Composite Joints

In view of the application status and technical challenges of steel–wood composite joints in architecture, this paper proposes an innovative connection technology to solve issues such as susceptibility to pry-out at beam–column joints and low load-bearing capacity and to provide various reinforcement methods in order to meet the different structural requirements and economic benefits. By designing and manufacturing four groups of beam–column joint specimens with different reinforcement methods, including no reinforcement, structural adhesive and angle steel reinforcement, 4 mm thick steel sleeve reinforcement, and 6 mm thick steel sleeve reinforcement, monotonic loading tests and finite element simulations were carried out, respectively. This research found that unreinforced specimens and structural adhesive angle steel-reinforced joints exhibited obvious mortise and tenon compression deformation and, moreover, tenon pulling phenomena at load values of approximately 2 kN and 2.6 kN, respectively. However, the joint reinforced by a steel sleeve showed a significant improvement in the tenon pulling phenomenon and demonstrated excellent initial stiffness characteristics. The failure mode of the steel sleeve-reinforced joints is primarily characterized by the propagation of cracks at the edges of the steel plate and the tearing of the wood, but the overall structure remains intact. The initial rotational stiffness of the joints reinforced with angle steel and self-tapping screws, the joints reinforced with 4 mm thick steel sleeves, and the joints reinforced with 6 mm thick steel sleeves are 3.96, 6.99, and 13.62 times that of the pure wooden joints, while the ultimate bending moments are 1.97, 7.11, and 7.39 times, respectively. Using finite element software to simulate four groups of joints to observe their stress changes, the areas with high stress in the joints without sleeve reinforcement are mainly located at the upper and lower ends of the tenon, where the compressive stress at the upper edge of the tenon and the tensile stress at the lower flange are both distributed along the grain direction of the beam. The stress on the column sleeve of the joints reinforced with steel sleeves and bolts is relatively low, while the areas with high strain in the beam sleeve are mainly concentrated on the side with the welded stiffeners and its surroundings; the strain around the bolt holes is also quite noticeable.

Assessing Feasibility and Performance of Ultrasonic Guided Wave–Based Numerical–Experimental Methodology for Debonding Monitoring of Adhesive Joints: Application to an Internal Beam of a Battery Box

Assessing Feasibility and Performance of Ultrasonic Guided Wave–Based Numerical–Experimental Methodology for Debonding Monitoring of Adhesive Joints: Application to an Internal Beam of a Battery Box

Significantly improves the mechanical strength of aluminum alloy adhesive joint through electrochemical pretreatment in environmentally friendly medium

Significantly improves the mechanical strength of aluminum alloy adhesive joint through electrochemical pretreatment in environmentally friendly medium

Fatigue Behaviour of Mechanical Joints: A Review

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.

Effect of bonding defects on heat transfer and creep response of microprocessor-heatsink adhesive joints

Efficient thermal management in microelectronic assemblies is crucial for the optimal performance and reliability of microprocessors. This study investigates the thermal, static, and creep performance of pressure-sensitive adhesives (PSAs) used in bonding heatsinks to microchips, focusing on the impact of adhesive coverage on thermal conductivity, mechanical strength, and long-term deformation under sustained loads. Shear loading, specifically analyzed due to the prevalence of shear stresses in vertically oriented microelectronic assemblies, is critical for understanding the long-term reliability of these bonds. The thermal analysis revealed that perfectly bonded heatsinks enhanced heat dissipation, with only a minor reduction in thermal conductivity observed due to incomplete adhesive coverage. Static tests demonstrated that perfectly bonded samples exhibited better load-bearing capacity overall, although joints with defects showed higher calculated stress due to the reduced bonded area at failure, with a 21% reduction in load-bearing capacity at room temperature and a 3.5% reduction at high temperature for joints with adhesive loss. Creep tests showed that at room temperature, the time to failure decreased by approximately 150% for samples with adhesive defects, while at high temperature, the reduction was over 66%. The study found that creep life is more sensitive to defects at lower temperatures, where adhesive loss has a more pronounced impact on performance. A predictive surface model was developed to estimate time to failure based on creep stress and temperature.