Lap Shear Joints Research Articles

Joule debonding of carbon reinforced polymer (CFRP) lap shear joints bonded with graphene nanoplatelets (GNPs)/epoxy nanocomposites

The potential of Joule heating CFRPs joints bonded with conductive graphene/epoxy nanocomposites as adhesives for a selective debonding was investigated. To ensure a localized softening of the bondline without altering the adherend’s structure, the epoxy used in the adhesive’s formulation was chosen to have a considerably lower Tg than the adherend. Joule heating the bondline considerably reduced the lap shear strength (LSS) relative to when the test was performed at room temperature, due to thermally induced structural changes promoted in the polymer network, which was consistent with the nanocomposites’ thermomechanical behavior predicted by DMTA. The minimum LSS value was reached in the vicinity of the adhesive’s Tg, allowing an ease deconstruction of the joints. SEM characterization of their fracture surfaces revealed that by controlling the adhesive’s formulation and their Joule heating the joints’ failure mechanism can be tuned to ensure the recovery of undamaged adherends that can be reused.

Influence of post-processing methods on bond-slip behavior of nonlinear Fe-SMA lap-shear joints

Prestressed bonded strengthening for structures employing iron-based shape memory alloy (Fe-SMA) has been proven promising. Analyzing adhesively bonded joints necessitates a thorough understanding of the bond-slip behavior. However, when examining the bond-slip behavior of Fe-SMA-to-steel joints comprising nonlinear adhesives, the “forward” and “backward” post-processing methods, representing the current state-of-the-art, produce a trilinear and a trapezoidal bond-slip pattern, respectively, which is inconsistent. To address this inconsistency, the current study investigates the bond behavior of Fe-SMA-to-steel joints, with a particular focus on the bond-slip behavior. Two finite element (FE) joints, one featuring a linear adhesive and the other comprising a nonlinear adhesive, are modeled and compared against physical tests from literature. The “forward” and “backward” processing methods are used to analyze the bond behavior of the two FE joints. Eventually, the aforementioned inconsistency is resolved; a triangular and a trapezoidal bond-slip pattern are characterized for Fe-SMA-to-steel lap-shear joints with linear and nonlinear adhesives, respectively. The trilinear bond-slip behavior is concluded as a result of error accumulation and propagation during the “forward” processing. A hybrid post-processing method, which takes the advantages of both the “forward” and “backward” processing methods, is further proposed for inferring the full-range behavior; the resulting experimental behaviors closely align with simulations using a trapezoidal bond-slip model as input. A comparison against carbon fiber reinforced polymer (CFRP) lap-shear joints demonstrates similar bond-slip characteristics between Fe-SMA and CFRP lap-shear joints.

Effects of Carbon Fiber Reinforced Plastic Laminate on the Strength of Adhesive Joints

Carbon fiber composites are being widely considered for many classes of heavily loaded components. A common feature of such components is the need to introduce local or global loads into the composite structure. The use of adhesive bonding rather than mechanical fasteners offers the potential for reduced weight and cost. The use of carbon fiber reinforced plastics (CFRP) for the repair of steel structure is also advantageous, for example to avoid welding or bolting which can weaken structure and add fire risk. This study is based on adhesive bonded double lap shear (DLS) joints where the inner adherend is steel and the outer adherend is cross plies unidirectional (UD) CFRP. Overlap lengths of 25-125 mm with CFRP thickness of 3 and 6 mm were considered and two different orientation angles [0o,90o] and [90o,0o] laminates have been considered. The overall objectives of the paper are to investigate the delamination of the CFRP laminates within the DLS joints under quasi-static loading and both experimental and numerical techniques were used. The numerical study was based on 2-D model using strength-limit method, taking into consideration the UD properties of the plies and the resin layers separating these. As a result, it was concluded that the data obtained from 2-D finite element analysis were coherent with experimental results and additional to that fiber orientation angles of the laminate markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite

Improved mechanical and fire-retardant properties of fiber-reinforced composites manufactured via modified resins and metallic thin films

Fiber-reinforced polymeric composites have been extensively used in different industrial applications because of their excellent mechanical and other properties but have lower tolerance levels for fire and lightning damage. The thermal, mechanical, and electrical conductivity of these composites can be substantially increased using some thin metallic films for higher fire resistance. The objective of this study was to develop fire-retardant fiber-reinforced composites using modified resins and metallic copper (Cu) thin films and test and characterize the mechanical and thermal properties of these prepared composites. Standard hand wet layup process was used to manufacture composite panels, and then the flame retardant and other physical and chemical properties were determined before and after resin modification and surface metal film coatings. These modified resins and the conductive metallic films of the composite provided superior flame retardancy and higher mechanical strength. The prepared composite panels made from modified epoxy via 9,10-dihydro-9-oxo-10-phosphaphenanthrene-10-oxide (DOPO) inclusion and with metallic surface coatings passed the UL-94 vertical flame testing with a V-0 rating. This composite achieved an average flexural strength of 344.2 MPa, a mean tensile strength of 400.82 MPa, and a shear strength of 6.54 MPa for single lap shear joint studies. Fractography results also show better bonding of the matrix and fiber with no significant damage. This study may open new opportunities in various composite industries.

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.

Effect of die design on microstructure and mechanical joint strength in friction self-piercing riveted AA7055-T76 and AA7055-T76

In the present study, a unique friction self-piercing riveting (F-SPR) was applied to join high-strength, low-ductility aluminum alloy (AA) 7055-T76 and AA7055-T76 to mitigate a cracking issue. Also, the effect of die design on both joint formation and the mechanical joint performance were investigated. A crack-free joint was achieved when joining AA7055-T76 and AA7055-T76 by F-SPR. As the bottom diameter of the die increased, the mechanical interlocking distance initially increased then became almost saturated. At the same time, the solid-state bonding gradually disappeared, and the lap-shear fracture changed from bottom aluminum fracture to rivet pull-out with partial bottom aluminum fracture. The average maximum lap-shear joint strength of 11.57 kN and cross tension of 5.65 kN were achieved from the D2 die design owing to the combined contributions from high mechanical interlocking distance and good solid-state bonding at the joint interface. Ultrafine grain refinement was observed at the region next to the rivet shank outer surface and along the materials flow line between the top and bottom aluminum sheet in the rivet cavity. Because of the same joint-process parameters, the hardness profile at the joints made by different dies did not show obvious differences. As the distance from the base metal to the rivet outer surface decreased, frictional heat caused the hardness to initially decrease from 190 to 150 HV in the heat-affected zone. Hardness increased up to 175 HV in the thermomechanical affected zone (TMAZ-I) owing to large plastic deformation.

Effect of sintering temperature on ratcheting-fatigue behavior of nanosilver sintered lap shear joint

Purpose The paper aims to study the effect of sintering temperature on the microstructure, shear strength and ratcheting fatigue life of nanosilver sintered lap shear joint. In addition, the Gerber model is used to predict the ratcheting fatigue lives of nanosilver sintered lap shear joints at different sintering temperatures. Design/methodology/approach In this paper, the nanosilver sintered lap shear joints were prepared at three sintering temperatures of 250 °C, 280 °C and 310 °C. The bonding quality was characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscope and shear tests, and the long-term reliability was studied by conducting ratcheting fatigue tests. In addition, three modified models based on Basquin equation were used to predict the ratcheting fatigue life of nanosilver sintered lap shear joint and their accuracies were evaluated. Findings When the sintering temperature is 250°C, the nanosilver sintered lap shear joint shows the porosity of 22.9 ± 1.6 %, and the shear strength of 22.3 ± 2.4 MPa. Raising the sintering temperature enhances silver crystallite size, strengthens sintering necks, thus improves shear strength and ratcheting fatigue life in joints. In addition, the ratcheting fatigue lives of the joints sintered at different temperatures are effectively predicted by three equivalent force models, and the Gerber model shows the highest life prediction accuracy. Research limitations/implications The sintered silver bondline is suffering a complex stress state. The study only takes the shear stress into consideration. The tensile stress and the combination of shear stress and tensile stress can to be considered in the future study. Practical implications The paper provides the experimental and theoretical support for robust bonding and long-term reliability of sintered silver structure. Social implications The introduced model can predict the ratcheting fatigue lives of the joints sintered at different temperatures, which shows a potential in engineering applications. Originality/value The study revealed the relationship between the sintering temperature and the microstructure, the shear strength and the ratcheting fatigue life of the joint. In addition, the Gerber model can predict the ratcheting fatigue life accurately at different sintering temperatures.

Comparative assessment of failure in single shear lap joints fabricated using various joining techniques

The current research endeavour reports the performance of single shear lap joints of flax/PP composite laminates. The joints were fabricated using mechanical joining, fusion bonding (ultrasonic and hot plate joining), and hybrid joining techniques (mechanical/ultrasonic joining and mechanical/hot plate joining). In case of the mechanical and hybrid joining, the effect of the bolt size, and number of bolts (single and double) on the tensile failure load was investigated. Pertaining to mechanical joining, the large bolt size and double bolts recorded higher tensile failure load compared to smaller bolt size and single bolt, respectively. Whereas with double bolts, no increase in the tensile failure load was observed for the hybrid joints, due to reduction in bonded area. The hybrid joints (mechanical/ultrasonic) recorded the maximum tensile failure load compared to all other type of joints. The load-extension behaviour and failure of joints was also examined. Expect mechanical joints, all other joints exhibited structural type of failure. In contrast, the mechanical joints resulted in a net-tension failure mode with failure line passing through the hole. However, the thermal decomposition and crystalline behaviour (XRD spectra) of developed joints did not vary significantly. The morphology of failed joints was examined using scanning electron microscope.

Evaluating the joinability of thin-walled high pressure die cast aluminium for automotive structures using self-piercing rivets

This paper is the first to report successful application of self-pierce riveting (SPR) in thin-walled high pressure die cast (HPDC) aluminium for use in automotive applications. HPDC fabricated AA356x coupons were joined to conventional rolled RC5754 material. A set of industry-relevant joint stacks were created. Priority stacks included cast material as the upper layer. More challenging joints were also fabricated with cast material as the lower layer. Automotive industry key performance indicators were used to assess joint integrity. The key results and recommendations were:•HPDC aluminium was revealed to be able to be joined to rolled aluminium according to vehicle manufacturer automotive standards.•Process boundaries were established for satisfactory SPR joints across a range of material thicknesses and stack types.•SPR joint solutions were proven in the most challenging stacks with cast material as a bottom layer.•Greater variability in the joint key performance indicators was observed in stacks where the cast alloy is the top layer.•Microstructural analysis of both AA356x and RC5754 revealed differences in grain structure and hardness and it is proposed that this accounts for the increased variability.•Strength testing of lap shear joints demonstrated the mechanical effectiveness of an SPR joint including cast material. Under normal vehicle operating conditions, the performance of joints including cast material was equivalent to that of rolled material only joints. Following yielding, joints including cast material suffered a more brittle failure mode leading to differences in performance under crash scenarios.

Effect of nanoparticle type and processing technique on the performance of lap shear joint of epoxy nanocomposite adhesives

Effect of nanoparticle type and processing technique on the performance of lap shear joint of epoxy nanocomposite adhesives

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.

Lap shear properties of CF/PEKK composites through nanoparticle-enhanced adhesive joints

This study investigates the effects of incorporating halloysite nanotubes (HNTs) into polyetherimide (PEI) adhesive for carbon fiber/polyetherketoneketone (CF/PEKK) composite joints. The CF/PEKK substrate is fabricated through an oven consolidation process, while PEI adhesive films with varying HNTs loadings (0.5, 1 and 3[Formula: see text]wt.%) are prepared using solvent casting with [Formula: see text]-butyrolactone. Homogeneous dispersion of HNTs in PEI is achieved through magnetic stirring and IR heating. The resulting film is hot pressed to form a 100[Formula: see text][Formula: see text]m thick film, and adhesive lap shear joint specimens are manufactured through oven consolidation. Morphology and dispersion of HNTs in PEI are analyzed using SEM and EDS, revealing favorable dispersion at 0.5[Formula: see text]wt.% HNTs and aggregation at higher loadings. Differential scanning calorimetry (DSC) is employed to study the glass transition temperature (Tg) of PEI, showing decreased Tg for solvent-cast PEI and increased Tg with HNTs incorporation. This increase is attributed to the constrained mobility of polymer chains due to HNTs’ influence. Lap shear strength (LSS) is evaluated, demonstrating enhancement with HNTs incorporation: 0.5[Formula: see text]wt.% HNTs (+12.5%) > 1[Formula: see text]wt.% HNTs (+8.33%) > Pure PEI > 3[Formula: see text]wt.% HNTs (−12.5%). The study attributes this enhancement to HNTs’ reinforcement and chemical interactions with PEKK. Aggregation tendencies at 3[Formula: see text]wt.% HNTs lead to decreased LSS. SEM-EDS analysis of fractured specimens indicates a multifaceted bonding joint interface involving PEKK, PEI and HNTs. CF/PEKK composites show adhesive, cohesive and adherend failure modes, with adherend failure being dominant. Notably, fabric-like textures and plastic deformations in PEI with 0.5[Formula: see text]wt.% HNTs contribute to enhanced LSS, while higher HNTs content leads to cohesive failure due to aggregation. This study provides insights into optimizing composite adhesive systems by harnessing nanotube reinforcement and controlling dispersion, thereby influencing interfacial strength.

Mechanical response of carbon fiber reinforced epoxy composite parts joined with varying bonding techniques for aerospace applications

As a result of the widespread use of composite materials in primary structures of aerospace platforms, composite joining became more crucial. This study addresses the effect of joining methods on the strength of composite joints experimentally, numerically and analytically. Single lap joint shear strengths of carbon fiber reinforced epoxy composite parts joined by mechanical fastening with a pop and solid rivet, secondary bonding with a paste adhesive, co-curing and co-bonding techniques were compared. In addition, the effect of adhesive thicknesses (0.2, 0.4, 0.6, 0.76 mm) on the single lap shear strength was investigated. Carbon fiber reinforced composite (CFRP) samples were produced according to the ASTM 5868 standard. After the production of samples with varying joining methods, single lap shear tests were implemented. Moreover, the interface damage in the composites was examined by use of a scanning electron microscope (SEM) for the purpose of studying the damage mechanism. Fracture mechanisms corresponding with bonding methods were also assessed by examining the fracture surface of the composite samples. Furthermore, results were analyzed by Hypermesh, ABAQUS and ESAComp. For instance, the co-bonded sample with an adhesive film exhibits an experimental shear strength of 24.03 MPa which deviates only 3 % from the numerical expectation.

Code-conforming fatigue life assessment of riveted lap shear joints

Recent studies highlighted the importance of an accurate assessment of the remaining life of historical steel riveted bridges to plan and design their maintenance. Such structures are usually prone to fatigue damage due to the high number of cumulated cyclic stresses over their service life. Currently, limited guidelines are available for evaluating the fatigue strength of riveted connections. According to the JRC-ECCS document Assessment of Existing Steel Structures: Recommendations for Estimation of Remaining Fatigue Life, the fatigue capacity of riveted connections should be evaluated through the fatigue class 71, whose prediction may be excessively conservative. Therefore, this paper summarizes the results of a theoretical study and an experimental campaign aimed at characterizing the high-cycle fatigue of riveted shear splices. Experimental fatigue results have been collected from the literature, and a database has been built, including material property, loading condition, riveting process, and geometry information. The collected data and those obtained from the performed tests have been statistically elaborated to investigate the influence of such parameters on their fatigue strength. Finally, comparisons with the recommended fatigue classes are provided to discuss their suitability in predicting the fatigue strength of the investigated riveted connections.

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.

Prediction of the strength of adhesive lap joints. An investigative review

The principal methods of predicting the strength of lap shear bonded joints have been introduced for metallic and composite adherends. The early theories of Volkersen and of Goland and Reissner provided indications of the shear and transverse [peel] stresses. These equations were not easy to use and were increasingly displaced by finite element analysis [FEA]. The importance or otherwise of the high stresses around the embedded corner of the unloaded adherend were examined and shown to be the most likely cause of initial cracking, but not necessarily of joint failure. By combining an extensive experimental programme of testing both adhesives and joints with FEA, knowledge was gained of the reasons why lap shear joints fail. Some simple equations were developed with failure criteria based on yield of the adherend and/or the adhesive which produced predictions in good agreement with experimental results. Finally, the bonding of composites was considered, and it was shown that the key factor is the transverse tensile strength of the composite.

Fatigue crack initiation life prediction using different plasticity models in cold expanded AL-alloy plates utilized in double shear lap joints

Cold expansion of fastener holes is a recognized technique for enhancing the fatigue life of holed plates utilized in detachable joints. This method involves introducing compressive residual stress around the holes, which has proven to be effective in improving the structural integrity and longevity of such components. In this research, the role of using different plasticity models in finite-element simulations of cold expansion (CE) in determining residual stress distribution and predicting the fatigue life of lap joints was investigated. Finite-element simulations were conducted to analyze the distribution of residual stress in cold-expanded Al-alloy 2024-T3 plates utilized in double-shear lap joints. Three time-independent plasticity models, specifically multilinear kinematic hardening, multilinear isotropic hardening (M.L.I.H) based on monotonic tensile tests, and nonlinear combined hardening models derived from saturated hysteresis stress and strain loops, were employed in the simulations. These models allowed for an accurate determination of the residual stress distribution in the plates. In finite-element simulations, two CE sizes of 1.5% and 4.7% were employed to create residual stresses. In the simulations, after creating residual stress by CE, remote sinusoidal loads are applied to the joints corresponding to the previously conducted fatigue tests in order to obtain stress and mechanical strain distributions. In order to predict the fatigue life, four different multiaxial fatigue criteria (Smith–Watson–Topper, Glinka, Kandil–Brown–Miller, and Fatemi–Socie) were employed, using the stress and strain distributions obtained from the finite element simulations with the different plasticity models. The simulations yielded varying stress and strain distribution results for the multilinear kinematic and M.L.I.H models, while the results of the nonlinear combined hardening model fell between the other two models. Notably, the fatigue life prediction based on the nonlinear combined hardening plasticity model closely matched the experimentally observed fatigue lives, with an absolute percentage deviation of 24.8%.

An experimental and simulation study of RGO effects on mechanical behaviour of structural adhesive and lap shear joints strength

The research investigates the effects of adding Reduced Graphene Oxide (RGO) at various weight fractions (0.25, 0.5, 0.75 and 1 wt%) on mechanical properties of high strength structural adhesive Araldite©️ 2011 and lap shear strength of adhesive joints. For uniform dispersion of RGO across adhesive, an extensive solution mixing technique was carefully carried out for the preparation of RGO/Epoxy combinations. Two types of lap joints: single lap joint (SLJ) and double lap strap joint (DLSJ) were fabricated. The joints were fabricated using Al 5083 as adherends. The adherends were treated with phosphoric acid anodization (PAA) before joining. A comparison of the strength properties was made after tensile testing of the adhesive specimens and lap joints. In the case of adhesive samples, an increase in mechanical properties was observed at lower concentrations. A maximum increase of 9.5% in the tensile strength and 128% in toughness characteristics was observed with the addition of 0.25 wt% RGO. A maximum improvement of 24% for SLJ and 25% for DLSJ was observed at the same filler percentage. Chemical analysis was conducted using Fourier-Transform Infrared Spectroscopy (FTIR), while dispersion analysis was carried out using Ultraviolet–Visible Spectroscopy (UV-VIS-Nir). Digital and Scanning Electron Microscopy (SEM) techniques were utilised in close examination of the fracture surface at high magnification. A finite element analysis based on cohesive zone modelling (CZM) was performed to predict the failure load characteristics of lap joints. Finally, a comparison of strength and fracture behaviour of RGO with GNPs and MWCNTs was critically discused.

To measure is to know: Evaluating indirect measurement techniques for observing the damage tolerance behaviour of spot welded thermoplastic composites

In thermoplastic composite joints with a circular ultrasonic spot weld, the damage growth is located at the interface between the joined components. This means that any damage in these joints is invisible from the outside. This experimental study compares three different in-situ methods to measure the damage growth indirectly. The motivation lies in the potential benefits of using multi-spot welded joints for increased damage tolerance and the need to prove the damage arresting and damage progression behaviour for certification. The current study focused on measuring the damage in single-spot welded Single Lap Shear (SLS) joints during fatigue test with the global specimen compliance, the local out-of-plane displacement and the local strain on the surface. Digital Image Correlation (DIC) measurements were used to obtain the local quantities. The results showed that the local quantities are better suited to obtain detailed information on the damage state. The local surface strain showed more distinct features that facilitate the recognition of damage locations. The benefits and challenges of all methods are discussed as well as the difference in the level of detail, generalization and the prior knowledge necessary to obtain the damage state.

Study on Tensile Performance of Double-Bolted Joints between Carbon Fiber Reinforced Polymer Plate and Aluminum Plate

Carbon fiber reinforced polymer (CFRP) with high specific strength, specific modulus, and other outstanding properties, which could be used in aerospace, shipbuilding, and railway. The joint of carbon fiber composite material plate and metal material plate plays an important role in the overall performance of the structure. In this paper, a carbon fiber reinforced polymer (CFRP) progressive damage model is developed based on composite laminate theory and 3D Hashian theory. The model of the double bolt single lap joint shear connection is established for the CFRP plate and the finite element method is used to carry out the stress analysis and failure prediction of the lap structure. The effect on structural performance under tensile conditions was studied through the change of double bolt spacing. The results show that the decrease in bolt row spacing can lead to the interference effect between holes. In addition, the progressive damage of the composite plate is located near the center line of the bolt hole.