Single Shear Research Articles

Fracture behaviour of Sn-58Bi alloy reinforced by activated bamboo charcoal

Sn-Bi solders are considered by PV manufacturers as acceptable Pb-free alternative due to its low operating temperature and cost, despite being prone to brittleness caused by coarse Bi phases. Bamboo charcoal (BC) is a sustainable and environment-friendly resource with high surface area and its addition to Sn-Bi solder meets the requirement of a green solder, in line with environmental regulations. This study aims to improve the shear strength and reduce brittleness of the Sn-Bi solder alloy by using a sustainable reinforcement, the activated bamboo charcoal. Sn-58Bi solder paste was reinforced with 0.25, 0.50, 0.75 and 1.00 wt.% of activated BC, respectively and reflowed to create a single lap shear joint. Aging response was determined through accelerated aging at 120 °C for 7 days and 14 days. Shear strength of the joints increased as the activated BC content increased in the as-reflowed condition and there was lower degradation in shear strength for heat-aging specimens compared to pure Sn-Bi solder. No failures occurred via Mode 3 when the as-reflowed samples contained 0.50 wt.% or more of activated BC, and the 7- and 14-day heat-aged samples were free from Mode 3 failures when the activated BC composition was at 0.75 wt.% and above. Fracture surfaces showed transitions from flat and smooth surface to elongated-dimple structures even with just 0.25 wt.% of activated BC addition. While prolonged heat-aging increased cleavage presence, increasing amounts of activated BC reduced facet numbers and dimple sizes, indicating successful suppression of Bi phase segregation.

Bond and tensile behaviour of textile reinforced mortars with traditional and alternative matrices

Reinforced and prestressed concrete structures frequently need to be repaired and strengthened during their service life due to corrosion deterioration and other pathologies. Composite materials, such as textile reinforced mortar (TRM), have emerged as a promising solution for restoring or improving the load bearing capacity of structural concrete. Previous studies have demonstrated that the effectiveness of this strengthening technique relies mostly on the bond between the textile and the matrix as well as on the bonded length to the substrate. The research presented in this paper aims to evaluate the efficiency of bond characteristics as well as the mechanical properties of various TRM systems. Carbon and basalt textiles were investigated along with conventional cement mortar and alternative mortars with short glass or synthetic fibres. To examine the bond behaviour of each system, a single lap shear test configuration was used. Tensile testing was carried out using a clevis grip or a clamping configuration. The tension and bond properties obtained from the tests are analysed and compared, and recommendations are presented regarding the bond and tensile test setups.

Experimental study on thermal matrix composite for seismic-energy upgrade of masonry buildings

The existing building stock consists mainly of masonry constructions built long before modern seismic regulations and the issue of energy saving. As a result of the well-known problems related to climate change and the need to reduce energy consumption, the issues of sustainability and reducing the environmental impact of the construction industry have become increasingly relevant. In this context, the present research addresses an integrated way for both structural and energy upgrade of masonry buildings. Specifically, innovative fibre-reinforced composite materials assembled by using lime-based thermal matrices combined with a balanced high-strength basalt fibre were experimentally investigated at the Laboratory of the University of Florence. These composite materials are identified by the acronym FRLM (Fiber Reinforced Lime Matrix). Initial work involved the selection of thermally efficient and compatible matrices, and then, the composite materials were investigated through tensile tests and single shear tests in order to evaluate their bond performance. Different bond lengths were considered with the goal of identifying the effective one.

Influence of glass-fiber epoxy coating on bond behavior of FRCM systems with different internal and external CMLs

FRCM composite systems display outstanding capabilities for the reinforcement of existing structures. Their modeling is challenging for the numerous damage scenarios and sources of non-linearity; also, test methods for mechanical characterization are still debated. In this study, six different FRCM systems were considered by combining the same glass-fiber textile, dry or epoxy-coated, and three different matrices based on cement, lime, and gypsum binders. The experimental results of the single shear tests highlighted the beneficial effect of the epoxy resin coating that greatly improves the fiber-matrix adhesion capacity in terms of stress, although nullifying the smooth softening behavior, resulting in brittle failure of the textile. Then, an analytical model aimed at calibrating the CMLs and predicting the corresponding global load slip diagram of the six systems is proposed. The assumptions considered are that the internal and external interfaces experience two different shear stress-slip laws and that the brick and both the matrix layers are rigid.

Interfacial behavior of hybrid-bonded CFRP-to-concrete joints

Hybrid-bonded (HB) systems are employed to anchor carbon fibre reinforced polymer (CFRP) laminates to concrete structures and delay their premature debonding failure mode by generating compressive stresses on the joint. However, although previous research on these strengthening systems exists, the optimum parameters that minimize the potential for premature debonding failure and maximize the ultimate load still need to be investigated.In this work, the feasibility of decoupling the effect of decohesion and friction of a HB CFRP-to-concrete joint is assessed through experimental and numerical analysis. To this end, single shear tests are performed on concrete specimens strengthened with externally bonded reinforcement (EBR) and HB-CFRP precured laminate. Besides, a numerical procedure, based on the finite difference method and a metaheuristic optimization algorithm, is utilized to obtain the bond-slip law that describes the constitutive behaviour of both systems. Moreover, the separated contributions of the cohesion of the adhesive joint and the friction induced by the external compressive stresses normal to the composite surface are analysed separately, and separated cohesive and friction stress-slip laws are obtained. The experimental behaviour of the full anchoring system is compared against that obtained by combination of the separated cohesive and friction contributions. The method represents progress in examining how different anchoring parameters, including the size (width and thickness) of the anchor plate and the torque applied to the bolts, influence the performance of the anchoring system in an efficient and systematic manner.

Metal-composite hybrid joint adhesion and testing optimization for electric vehicle applications

ABSTRACT Lightweight is a critical feature in automotive applications, especially in electric vehicle applications due to the heavyweight of batteries, thus contributing to improve vehicle efficiency. Multi-material solutions were studied in this paper as a strategy for lightweighting, focusing on the improvement of metal-composite joints obtained by overmolding through the comparison of different laser treated textures and processing parameters. In addition, testing methods to assess the adhesion of these joints were analysed. Firstly, steel surface treatment was carried out by pulsed laser radiation producing different patterns. Secondly, over injection of the composite material based on polyamide 6.6 with 40% recycled carbon fiber was carried out with different processing parameters. The mechanical performance of the joints was assessed through shear-strength analysis, and the morphological analysis was carried out. As outcome, the optimal combination of surface treatment and processing parameters was selected. Finally, a finite element analysis was carried out to evaluate comparatively the suitability of a testing method proposed as an alternative to the standard single lap shear tests, with a configuration that facilitates the specimens manufacturing and test execution. As a result, the adequacy of the method for the assessment of the shear strength of this type of joints was demonstrated.

Study on the Difference of Fracture Extension in Hydraulic Fracturing of Marine and Continental Shales Based on Optical Scanning Technology

After hydraulic fracturing, the geometric characteristics of rock morphology is a crucial means for evaluating the effectiveness of fracture stimulation in enhancing production. In order to quantitatively analyze the surface undulations of marine and continental shale morphology further following hydraulic fracturing, a method for calculating the three-dimensional fractal dimension of fracture surfaces based on optical scanning technology is proposed. This method involves the acquisition of point cloud data using a 3D surface scanner. The obtained data are subsequently subjected to smoothing processes, followed by the reconstruction of the three-dimensional representation of the fractures. The box-counting dimension algorithm is employed to calculate the fractal characteristics of post-fracture morphology. The research results indicate that marine shale, due to its higher proportion of brittle minerals such as quartz and calcite, predominantly exhibits vertically oriented longitudinal fractures, perpendicular to the minimum horizontal stress. The average initiation pressure is 8% higher compared to continental shale, with an average fractal dimension of 2.24397. In contrast, continental shale, characterized by its high clay content and the development of natural fractures and bedding planes, is more prone to capturing hydraulic fracture features, resulting in predominantly single transverse shear fractures. The average fractal dimension is 2.087065, which is 7% lower than that of marine shale. These research findings offer a certain degree of guidance for the optimization of fracturing process parameters for different types of reservoirs.

Influence of high frequency on the fatigue life of metallic single lap joints

Polymer adhesives are known to exhibit time dependent mechanical behaviour, that becomes more and more evident approaching the glass transition temperature, Tg. When subjected to fatigue, bonded joint lifetime can be therefore affected by the loading frequency and amplitude. According to the literature, the influence of the frequency on the fatigue behavior manifests as a rise of the temperature in the adhesive due to the hysteretic heating, which is related in turn to Tg and to the viscoelastic properties of the adhesive. In this paper, cyclic loading was applied to single lap shear joints until failure at frequencies in the range of 70–90 Hz, that are little explored by the existing literature. The aim is twofold: on one side, to investigate the possibility to speed up fatigue tests in comparison to tests performed in the range of 7–9 Hz; on the other side, to explore the possibility to generate stress-life data in a range of number of cycles between 106 and 108, therefore two order of magnitude higher then usual, without exceeding with the time required for the tests. The joints were made with both aluminum and stainless-steel substrates bonded with a structural epoxy adhesive, to manufacture a Single Lap Joint (SLJ). Two loading ratios R (respectively 0.1 and 0.4, defined as the minimum over the maximum force of the fatigue cycle) and different load ranges were applied. Digital Image Correlation (DIC) technique was used to assess the presence of creep strains. A preliminary investigation consisting in a Dynamic Mechanical Analysis (DMA) of bulk adhesive for the range of frequency of interest, and in the measurement of the temperature of the adhesive layer during some selected fatigue tests was carried out. No significant changes of the viscoelastic properties of the adhesive were found for the frequency of interest, and, at the same time, temperature measurements revealed that the temperature increased by a few degrees, remaining in any case far from the glass transition temperature. The test results showed that only small effect due to the application of a high frequency cyclic loading on the fatigue life apparently occurs for tests carried out at the lowest load ratio, in particular when the applied loads were relatively low, and the number of cycles at failure relatively high. On the opposite, the results of tests carried out at the highest load ratio are affected by the loading frequency, and it has been related to the presence of significant creep deformation within the adhesive layer.

Application of single and multi-solid phase STFs to Twaron fabrics: evaluation of energy absorption performances

The present study aims to enhance the energy absorption performance of Twaron aramid fabrics by impregnating them with single and multi-solid phase shear thickening fluids (STFs). To investigate the energy absorption capacity of Twaron 200 and Twaron 460 fabrics, surface friction, yarn tensile, and ballistic tests have been performed. Silicon carbide (SiC), graphene nanoplate (GNP), and carbon nanotube (CNT) are utilized both individually and in hybrid forms to examine the impact of multi-solid phase STFs. The research reveals that STFs reinforced with SiC and GNP exhibit higher viscosity and rheological behavior compared to other hybrid nanoparticles. The addition of SiC and GNP reinforced STF (STF/SiC + GNP) suspension significantly increases the friction coefficient by approximately 82% for Twaron 200 and 120% for Twaron 460 in comparison to neat fabric. Moreover, the maximum yarn tensile strength of Twaron 460 is higher than that of Twaron 200 in both neat and STF impregnated fabrics. The research also states that STF impregnation procedure improves the ballistic performance of neat fabrics in both fabric types. The ballistic test results show an increase in the protective performance of STF impregnated fabrics reinforced with nanoparticles. The best ballistic performance is found in STF/SiC + GNP impregnated fabrics in Twaron 200 and Twaron 460 samples.

Plasma treatment on both adhesive tape and adherends for significantly enhanced CFRTP-related adhesive joints

Unlike existing literature that primarily concentrates on either the plasma treatment of adherends alone or solely on adhesive surfaces, this work leverages plasma modification of both adhesive in tape form and adherend surfaces to largely enhance the interfacial bonding between a thermoset-based adhesive tape and carbon-fiber-reinforced thermoplastic polymer (CFRTP) for structural bonding applications.By conducting single lap shear tests on adhesively-bonded AA6061-CFRPPA (carbon-fiber-reinforced polyphthalamide) dissimilar joints, it is shown that the plasma treatment of adherends alone can increase the lap shear strength (LSS) of the joints by 200% compared to non-treated counterparts. An additional plasma treatment of adhesive tape surfaces leads to even higher LSS improvement, reaching up to 315%, due to the formation of a denser cross-linked network of covalent bonds and a reduced area fraction of interfacial voids at the CFRPPA–adhesive interface.The highest plasma-enhanced LSS of the metal-CFRTP joints rivals that of metal–metal joints, which is typically stronger than the joints associated with fiber-reinforced polymers. This study is important for achieving strong CFRTP-related structural components bonded using adhesive tape, providing better compatibility with plasma treatment and other joining methods like riveting compared to adhesive paste or liquid.

Reaching Large Strains During Simple Shear Experiments Thanks to Sequential Re-Machining of the Free Edges

BackgroundThe simple shear experiment is widely used for the calibration of plasticity models due to straightforward post processing. The specimen can be as simple as a rectangular strip of sheet metal, but the maximum strain is limited by early initiation of fractures from the free edges. Avoiding this drawback has been a major motivation for the development of new specimens with optimized edge geometries or the in-plane torsion test, but at the cost of a more complex analysis of the test and often a reduction of the gauge section.ObjectiveThe objective of the present work is to overcome the initiation of fracture from the free edges during simple shear experiments. Our goal is to double the achievable maximum strain, while keeping the size of the specimen and the post processing simplicity of a standard simple shear test.MethodsA sequential single shear test is proposed, consisting of several two steps sequences on a notched geometry. First, an interrupted shear test is performed up to a specified displacement value. Then, the damaged free edges of the specimen are removed through milling. The specimen is then ready for the following sequence of shear and re-machining.ResultsExperiments are performed on three engineering materials, with up to five loading-machining sequences. The maximum attained effective strain is up to two times the one reached during a monotonic experiment. Numerical simulations are used to validate the shear stress and strain calculations from experimental measurements. Practical recommendations are derived for the choice of the displacement step size and Digital Image Correlation analysis.ConclusionIt is found that the maximum strain attained before the undesired failure of the specimen during simple shear test can be substantially extended through repeated re-machining of the specimen boundaries, enabling behavior identification at larger strains.

Net section tension capacity of high strength steel single shear bolted connections

Single shear bolted connections under tension usually exhibit out-of-plane deformation due to the inherent load eccentricity, resulting in significant stress concentration around the bolt holes and a stress gradient through the plate thickness. This effect is particularly pronounced in high-strength steel (HSS) connections due to the relatively lower ductility and tensile-to-yield strength ratio of HSS. However, it remains unclear whether this issue can lead to premature fracture in high strain regions before effective stress redistribution develops across the net section, subsequently reducing the ultimate load capacity of the HSS connections. To examine the above design issue, an experimental and numerical study on single shear bolted connections was conducted and reported in this paper. A total of 25 connections were tested, among which 17 were made of HSS (Q690 and Q960), and 8 were made of Q345 mild steel (MS). Based on a validated finite element (FE) model, a comprehensive numerical analysis was carried out to interpret the structural behaviour of the specimens and explore the influence of various design parameters on the ultimate tension capacity of single shear bolted connections. The findings revealed that, despite the existence of out-of-plane deformation in the steel plate, all connections (either MS or HSS) investigated in this study reached the theoretical net section resistance (the product of the net section area and the ultimate tensile strength). This is because (1) the relatively low ductility and tensile-to-yield strengths ratio of HSS materials are still sufficient to allow an effective stress redistribution across both the transverse net section and the plate thickness, and (2) the biaxial stress state around the bolt holes enhances the tension capacity of the net section. Finally, a statistical evaluation of the combined test and numerical data showed that the existing design equations for predicting the net section tension capacity of HSS (specified in EN 1993-1-12:2007 and prEN 1993-1-1:2020) can be safely applied to the design of HSS single shear bolted connections, even in scenarios where the tensile-to-yield strengths ratio of HSS is as low as 1.06.

Enhancing adhesive bond strength of CFRP/titanium joints through NaOH anodising and resin pre-coating treatments with optimised anodising conditions

Adhesively Bonded Carbon Fibre Reinforced Plastic (CFRP) and titanium alloy have been extensively used as a hybrid structure in modern aircrafts due to their excellent combination of mechanical properties and chemical stabilities. This study utilised NaOH anodising method to create micro-rough titanium surfaces for enhancing adhesive bonding between titanium alloy and CFRP laminates. A special and simple technique named Resin Pre-Coating (RPC) was also employed to improve the surface wetting of anodised titanium and grinded CFRP substrates. The influences of anodising temperature and duration on the surface morphology, wettability and adhesive bond strength were investigated. The single lap shear test results showed that the bond strength of specimens anodised at 20 °C for 15 min improved by 135.9% and 95.4%, respectively, in comparison with that of acid pickled and grinded specimens (without RPC treatment). Although increasing the anodising temperature and duration produced rougher titanium surfaces, the adhesively bonded joints were not strong enough due to relatively friable titanium oxide layers.

Evaluation and in-situ monitoring of interfacial property and thermal shock resistance of epoxy adhesive with different MWCNT contents for CFRP/GFRP hybrid composite

While glass fiber-reinforced composite (GFRC) and carbon fiber-reinforced composite (CFRC) (G/C) hybrid composites enable lightweight construction and improve mechanical properties, the difference in thermal strain between materials causes delamination at the interface. To address this issue, multi-walled carbon nanotubes (MWCNT) were applied to optimize thermal strain and provide a buffering effect. The mechanical properties were evaluated using the V-notched shear test, and the epoxy adhesive with 0.3 wt% MWCNT exhibited the best performance. The thermal strain of the materials was measured, and the epoxy adhesive showed similar thermal strain to the substrates as the MWCNT content increased. To evaluate adhesion properties and durability under different thermal shock conditions, single lap shear and cyclic short beam shear tests were performed. The load behavior of the specimens was monitored using electrical resistance (ER) mapping. It was determined that the epoxy adhesive with 0.3 wt% MWCNT exhibited superior adhesive properties and durability compared to other conditions under both thermal and cyclic loading.

Infrared-thermography measurement of temperature distribution in carbon fiber–reinforced polypropylene during ultrasonic welding

Herein, the temperature distribution during ultrasonic welding of carbon fiber–reinforced polypropylene (CF/PP) was investigated. The temperature distribution was assessed using a thermographic camera that specifically targeted the lateral aspect of the welded section of the adherend in the lap joint. In addition, single lap shear tests were performed on the resulting welded joints. The welding experiments confirmed that the amplitude of the sonotrode impacts both the temperature distribution during welding and the quality of the joint, eventually affecting the mode of failure. By applying the half-width method to the measured temperature distribution in the thickness direction of the adherend, we assessed the spread of the high-temperature region centered on the welding interface. In this study, at a small amplitude (36 μm), the half-width of the maximum temperature showed approximately twice higher slope than at other amplitudes, indicating a wider high-temperature range even at the same interface temperature.

Open time studies of cold curing polyurethane adhesives using a standardized spatula test setup suitable for near-production conditions

The presented studies introduce a new set-up and method to analyse the maximum open time of cold curing adhesives in a production environment. By using this new set-up, a manual spatula test, Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and a rheological method, the curing reaction of two cold curing two component polyurethane adhesives, were investigated. Furthermore, the effect of different joining times on the bonding behaviour were investigated using single lap shear samples.The lap shear tests showed that the prior problem for industrial applications is the dimensional accuracy rather than the adhesion to the substrates as all samples showed cohesive or substrate near cohesive failure even when joined after the maximum open time. All used methods showed a coherent curing behaviour for both adhesives. However, the derived times as well as their accuracies vary depending on the used method. Using the easy manual spatula test, the open time is determined by the sensory feelings of the testing person while pressing a wooden spatula into the adhesive bead and is often used in industrial applications. However, the accuracy lies only within 10–20 s especially for slow curing adhesives. In comparison, the ATR-FTIR method, which is based on the decrease of the isocyanate group during the reaction, showed shorter times, whereas longer times were determined by observing the complex viscosity increase of the rheological measurements. Even though the ATR-FTIR and rheological measurements showed reproducible times due to the required laboratory environment and testing procedure, they are therefore not suitable for production conditions. As the introduced new method is based on the manual spatula test, it is suitable for the production environment with the advantage of a good reproducibility. Furthermore, with this method decreasing maximum open times were observed for increasing bead cross sections.

Impact resistance of composite to aluminum single lap joints reinforced with graphene doped nylon 6.6 nanofibers

In this study, the low velocity impact resistance of pure and modified epoxy adhesives for single lap joints between aluminum and carbon epoxy composites was investigated. Epoxy resin was used as the adhesive, and pure epoxy resin was modified by adding graphene-doped nylon 6.6 nanofibers (1%, 3% and 5% by weight) and pure nylon 6.6 nanofibers produced by electrospinning. These nanofibers are reinforced to aluminum-composite single lap joints as a second interface according to ASTM D1002-10 standard. Thus, single lap joints were prepared using 5 different adhesives. To create the impact effect, some joints were subjected to impact at a low velocity (1.04 m/s). Then, all impacted and non-impacted samples were subjected to single lap shear testing at room temperature and constant load to determine the impact resistance. While the non-impact lap shear strength of the pure epoxy adhesive samples was 6.81 MPa, the non-impact shear strength of the samples using pure nanofiber reinforced epoxy adhesive increased by 71.3% to 11.67 MPa compared to the pure epoxy adhesive. When comparing the post-impact failure loads, it was determined that the addition of graphene increases the impact resistance. Furthermore, adhesive surfaces were examined by scanning electron microscopy (SEM) for damage analysis after the tensile tests and toughening mechanisms such as bridging, adhesive crack formation, nanofibers breakage was determined in epoxy adhesives reinforced nanofiber with graphene in different proportions by weight. In addition, the glass transition temperature, melting temperature, thermal decomposition temperature and mass loss of epoxy resin, and graphene doped/undoped N6.6 nanofiber-reinforced epoxy adhesives were analyzed by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) and it was determined that the addition of 3% GNP to N6.6 nanofiber reinforcement increased the thermal stability by 12.4%, the addition of 1% GNP to N6.6 nanofiber reinforcement increased the thermal resistance (glass transition temperature) by 34.9% compared pure epoxy.

Comparative study of the effects of galvanic corrosion on the strength and the failure of aluminium and stainless steel bolted joints

This paper investigates the effects of bimetallic insert on corrosion, material degradation, loading capacity, stress distribution, strain distribution and failure of aluminium-stainless steel lap shear bolted assemblies. The single bolt lap shear assemblies of aluminium and stainless steel plates were performed in two settings in one of them a bimetallic insert was used. Considering that the aluminium plays the role of sacrificial anode in the aluminium-stainless steel galvanic couple, a single bolt lap shear assembly joining two aluminium plates is also considered as a reference. The experimental measurements were determined by tensile-shear testing method for three different conditions: dry condition and two corrosion states corresponding to 6 weeks and 16 weeks of accelerated corrosion tests. To support understanding of the effects of preload and friction changes due to the formation of corrosion products, finite element simulations were performed with varying preloads and friction coefficients. The study demonstrated significant effects of corrosion on loading capacity, bolt rotation and failure mode. The tensile-shear forces measured for the aluminium-aluminium assembly and aluminium-stainless steel assembly after 6 weeks of accelerated corrosion tests increased compared to the tensile-shear forces measured in dry condition. The increase in tensile-shear forces was related to the formation of corrosion products, affecting the preload and the frictional behaviour of the contacting surfaces. In agreement with experimental observations, finite element simulations demonstrated an increase in the tensile-shear force with the increase of frictional forces. The application of bimetallic inserts considerably reduces the effect of corrosion on the measured tensile-shear force of corroded assembly compared to non-corroded assembly. However, it affects the force-displacement response and failure mode compared to the response of aluminium-stainless steel assembly without bimetallic insert due to its effects on the bolt rotation and stress distribution. This needs to be considered in the design of dissimilar material bolted assembly.

Bonded Behavior of Hybrid-Bonded CFRP to Heat-Damaged Concrete Interface

The reliable bond of CFRP to heat-damaged concrete is fundamental to ensuring cooperative working when the CFRP is applied for strengthening fire-damaged concrete structures. In this paper, the bond performance of hybrid-bonded (HB) CFRP to a heat-damaged concrete surface was investigated by using single shear tests. The concrete blocks were initially heat-damaged to temperatures of 100 °C, 200 °C, 300 °C, and 400 °C. The heat-damaged blocks were subsequently bonded with CFRP using the HB technique. The primary experiment parameters were the exposure temperature, the number of mechanical fasteners, and the bonded layers of CFRP. The test results show that the external-bonded (EB) and HB-CFRP joints with concrete exposed to a temperature of 400 °C were prone to fail with concrete shear-tension due to the decreased shear strength of concrete at high temperatures. The EB- and HB-CFRP joints with heat-damaged concrete anchored with no more than three fasteners present a higher bond than the reference joints with unheated concrete, while the HB-CFRP joints anchored with three fasteners provide a decreased bond capacity with the increase in exposure temperature. The utilization rate of single-layer CFRP joints with unheated concrete increased by 57.9%, 139.5%, and 136.8% with the mechanical fasteners in numbers of one, two, and three compared with the reference specimen. Accordingly, the bond capacity increased by 111.8%, 128.4%, and 186.7%. Finally, a model was proposed to estimate the bond strength of HB-CFRP joints with heat-damaged concrete.

Numerical Investigation of Failure in Epoxy-Based Adhesive Joints

Currently, adhesive bonding has been increasingly used in various industrial applications such as in automobile lightweight structures for multi-material assembly. However, adhesive joints show a complex failure behavior. Their failure modes can be either adhesive failure, cohesive failure, or mixed mode failure depending on their interfacial strength and also the strength of adhesive layer which also varies with hydrostatic pressure. In this study, the failure of the adhesive joints with an epoxy-based adhesive bonded to metallic substrates are investigated numerically using FEA. The damage evolution model is implemented in the finite element model to predict the failure of adhesive joints. The adhesive strengths under different states of stress for a damage evolution model are characterized using the modified Arcan fixture which is specifically designed to study of hydrostatic pressure effect on an adhesive behavior. The validation of the failure model is carried out with the results of single lap shear test. A good agreement is finally found between FEA and experiments.