Lap Shear Strength Of Joints Research Articles

Ultrasonic joining of carbon-reinforced polyamide with oak wood for manufacturing sustainable hybrid structures

The feasibility of manufacturing strong and lightweight hybrid joints of carbon fiber-reinforced polyamide (PA6-15CF) and oak wood using ultrasonic energy was successfully demonstrated. Before joining, a groove pattern was generated on the surface of the wood platelets by laser texturing. Wood platelets with and without texturing were joined with the polymer using the ultrasonic joining (U-Joining) process. Mechanical interlocking at the polymer-wood interface was improved, as the grooves and open vessels on the surface of the textured wood platelets were filled with the polymer composite. Therefore, the lap-shear strength of joints with textured wood was 9.2 ± 0.7 MPa, whereas the shear strength of joints with untextured wood was just 4.1 ± 0.8 MPa.

The influence of false heartwood of European beech (Fagus sylvatica L.) on tensile shear strength of lap joints

The influence of false heartwood of European beech (Fagus sylvatica L.) on tensile shear strength of lap joints

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.

Production of pyrolytic lignin for the phenolic resin synthesis via fast pyrolysis

Recycling of waste wood into resol type phenol-formaldehyde (PF) resins via fast pyrolysis was demonstrated. Waste wood collected from the building demolition site in Finland was pyrolyzed with 20 kg/h circulating fluidized bed pyrolysis pilot unit. Pilot was operated with high organic liquid yield (60 wt% on average) and the produced fast pyrolysis bio-oil was fractionated by water addition into aqueous phase and water insoluble phase. The obtained fractions were characterized, and the water-insoluble viscous lignin fraction was used in the synthesis of PF-resins. Commercial phenol was successfully replaced by pyrolytic lignin fraction at 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% producing resins of low in free formaldehyde content, but resins with high replacement ratio exhibited higher viscosities. The use of H2O/n-butanol mixture as solvent at a ratio 70:30 wt/wt% proved capable to prolong the storage time of the resin and helped to maintain the viscosity at acceptable values for at least 2 weeks before their use in the targeted application. Finally, the gluing performance of the resins was evaluated by measuring the tensile shear strength of lap joints formed by gluing 5 mm thick beech wood veneers. All the produced resins fulfilled a dry strength limit of ≥ 10 N/mm2. Wet strength limit ≥ 7 N/mm2 was fulfilled by the resins with the replacement ratio up 40 wt%, but resins with replacement ratio of 50 wt% had somewhat reduced wet strength. These results confirm a promising protentional application of pyrolysis derived lignin fraction in phenolic wood adhesives, at least in dry conditions.

A novel seal-flow multi-vortex friction stir lap welding of metal to polymer matrix composites

The friction stir lap welding (FSLW) of metal to polymer is a challenging work due to the unavoidable polymer overflowing. Facing this problem, a novel seal-flow multi-vortex friction stir lap welding (SM-FSLW) technology based on the subversively-designed multi-step pin was put forward. Choosing 7075 aluminum alloy and short glass fiber-reinforced polyether ether ketone (PEEK) as research subjects, the welding temperature, material flow, formation and tensile shear strength of dissimilar materials lap joint under the SM-FSLW were studied and compared with those under traditional FSLW based on the conical pin. The multi-step pin rather than the conical pin effectively hindered the polymer overflowing due to the formation of vortexes by the step, thereby attaining a joint with a smooth surface. Compared with traditional FSLW, the SM-FSLW obtained the higher welding temperature, the more violent material flow and the larger area with high flow velocity, thereby producing the macro-mechanical and micro-mechanical interlockings and then heightening the joint loading capacity. The tensile shear strength of lap joint under SM-FSLW was 27.8% higher than that under traditional FSLW. The SM-FSLW technology using the multi-step pin provides an effective way on obtaining a heterogeneous lap joint of metal to polymer with the excellent formation and high strength.

Study on synthesizing new urethane epoxy adhesives and their adhesive properties on different substrates

In this work, we prepared urethane epoxy adhesives from the reaction of glycidol and aliphatic diisocyanate, 4, 4-methylene bis (cyclohexyl isocyanate) (HMDI). We modified diglycidyl ether of bisphenol A (DGEBA) with this urethane epoxy and cured by maleic anhydride. We used Fourier-transform infrared (FTIR) for monitoring the reaction progress and confirming the unique structure. We measured the lap shear strength of joints, bonded with different weight ratios of urethane epoxy and DGEBA, on three different substrates aluminum, stainless steel, and glass fiber reinforced epoxy. The effect of substrates with varied materials was studied by scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX) with comparisons with X-ray photoelectron spectroscopy (XPS) results from other studies. The novel urethane-epoxy adhesive exhibited improvements in mechanical properties such as shear strength and elongation in comparison to common DGEBA-based epoxy adhesives.

Performance Augmentation of Epoxy Adhesives with TiN Nanoparticles.

In the current study, nanoparticles (NPs) of titanium nitride (50–70 nm) in varying amounts (0–4 wt %) were uniformly suspended in an epoxy solution and then used to cast the films of nanocomposites. The same formulations were used to prepare the lap shear strength joints using stainless-steel coupons with the help of standard molds and then employing the compression molding technique. The nanocomposites films were characterized for their physical properties, thermal stability, friction performance, and scratch hardness, while the lap shear strength of joints prepared using nanocomposites as nanoadhesives was evaluated. The failed surfaces of joints were investigated using scanning electron microscopy (SEM) to understand the failure modes, that is, micro-failure mechanisms, while the cross-sectional surfaces of fractured nanocomposites were investigated using SEM to identify the distribution of NPs. The increase in the contents of NPs in the epoxy led to an almost linear increase in the selected performance properties. The highest (70%) improvement in the lap shear strength was observed with 4 wt % NPs, which was correlated with an increase in the hardness of composites.

Influence humidity and heat on tensile shear strength of lap joints made of solid fir/spruce wood

Determination of tensile shear strength of lap joints is carried out according to three standards: BAS EN 205:2018 for adhesives used for non–load–bearing structures, and according to BAS EN 302-1:2014 for adhesives used for the manufacture of load-bearing structures and according to EN 14257:2019 for lap joints who are exposed to elevated temperatures. The paper presents the results of tensile shear strength of lap joints made of solid fir/spruce (Abies alba ssp./Picea abies spp). Tensile shear strength was tested in 4 groups of tests samples. The Group 1 consisted the samples were 7 days in standard atmosphere [20/65]. The Group 2 consisted the samples were previously soaked in water at (20 ± 5) °C, then recondition in standard atmosphere [20/65]. The Group 3 consisted the samples were previously 6 h soaked in boiling water 2 h, then soaked in water at (20 ± 5) °C; the samples tested in the wet state. The Group 4 consisted the samples were previously exposed to heat in a preheated fan oven, at (80 ± 2) °C, for (60 ± 2) min. The test results can be applied for gluing windows, doors, stairs, high-frequency gluing, veneering panels, etc.

Microstructure, wettability and strength of cryo‐deformed tin‐3.0 silver‐0.5 copper solder

AbstractThis project aims to assess the influence of cryogenic treatment prior to passing the solder sample through an equal channel angular pressing die in order to refine the microstructure of solder and thus, gain improvement of mechanical properties of solder joint. In this work, commercial tin‐3.0silver‐0.5copper solder alloy was subjected to severe plastic deformation by passing through the die for 1 pass, and prior to this, dipped in nitrogen for 10 minutes, 20 minutes and 30 minutes. Hardness and wettability of solder reflowed on bare copper substrate were measured along with strength of solder joint via lap joint shear strength test. Cryo‐deformed solder was found to have higher hardness, and wettability had also improved along with the strength of solder joint. Improvement could be due to grain refinement as observed in microstructure and also the more uniform distribution of eutectic network. Dipping for 10 minutes gave the best improvement, whereas longer dipping (20 and 30 minutes) seems to have deteriorating effect to the wettability and mechanical properties. Cryo‐deformation showed significant improvement on the wettability and mechanical properties of solder, and could potentially lead to higher reliability of solder joint.

Study of Corrosion, Structural, and Mechanical Properties of EN AW-6082 and EN AW-7075 Welded Joints.

The purpose of the work was to test the welded joints of aluminum alloys EN AW-7075 and EN AW-6082, which are used to join individual structural elements of car bodies, e.g., B-pillar with the body. The joints were made using the low-energy cold metal transfer (CMT) arc welding method. The results of the structure investigations of lap and butt joints, as well as tests of mechanical properties are presented. The influence of linear energy and the way of arranging materials in lap joints on the possibility of hot cracks occurrence has been demonstrated. The shear strength of lap joints was equal to 150 MPa, while the tensile strength of butt joints was equal to 375 MPa. The highest hardness reduction was observed in the heat affected zone (HAZ) from the EN AW-7075 alloy side in the range of 98 to 138 HV 0.05. In addition, a significant reduction of the corrosion resistance in the transition zone between HAZ and the base material (EN AW-7075 alloy) in the medium salinity environment, corresponding to the sea conditions according to ASTM G85 was indicated.

Thermal conductivity and mechanical performance of hexagonal boron nitride nanosheets-based epoxy adhesives

Thermosets possess diverse physical and chemical properties and thus they are widely used in various applications such as electronic packaging, construction, and automotive industries. However, their poor thermal conductivity and weak mechanical performance jeopardize their continual spread in modern industry. In this study, boron nitride nanosheets (BNNSs) were employed to promote both mechanical and thermal properties of epoxy nanocomposites. BNNSs and their epoxy nanocomposites were fabricated using in situ solvent ultrasonication and in situ polymerization, respectively. Thermal conductivity was enhanced by 153% increment in epoxy/BNNS nanocomposite at 7 wt% in comparison with neat epoxy. In parallel, Young’s modulus, lap shear strength, fracture toughness (K 1C ) and energy release rate (G 1C ) increased by 69%, 31%, 122% and 118%, respectively at 1 wt% BNNSs. Moreover, fatigue life and strength of lap shear joints were significantly improved upon adding BNNSs. A numerical model of the single lap shear joint was developed to validate the accuracy of the material constants obtained. Epoxy/BNNS nanocomposites exhibited an outstanding mechanical performance as well as high thermal conductivity giving them merits to widen their applications in electronic and automotive industry.

Effect of cellulosic fillers addition on curing and adhesion strength of moisture-curing one-component polyurethane adhesives

Abstract In this work, microcrystalline cellulose (MCC) and sawdust (SD) green fillers have been demonstrated as reactive fillers and moisture reservoirs for enhanced curing and adhesion strength of one-component moisture-curing polyurethane (PU) adhesives. The chemical reaction between the MCC or SD fillers and isocyanates present in the PU adhesives was tracked using Fourier-transform infrared spectroscopy (FTIR), while the joint strength was determined using lap-shear tests. The results showed that the addition of MCC or SD leads to an accelerated curing rate through the early consumption of isocyanates. The lap-shear strength of unreinforced PU adhesive joints was achieved in 12 hours. In turn, the curing time in MCC and SD reinforced joints was achieved in 5 hours. The addition of MCC and SD fillers also enhanced the lap-shear strength of the joints under full cure conditions. An autocatalytic growth model was used to describe the lap-shear strength variation with respect to curing time.

Optimization of microstructural morphology via laser processing to enhance the bond strength of Al-CFRP

Generating surface-functional microstructures is an effective way to enhance the bonding strength of metal and carbon fiber-reinforced polymer (CFRP). In this study, different microstructural morphologies consisting of two different patterns were generated on the aluminum alloy (A7075) surface via laser processing. The experimental results indicated that different microstructural morphologies contribute to the enhancement of the shear strength of lap joints. The maximum shear strength of these joints was almost four times stronger than that of lap joints without the microstructures. In addition, the investigation indicated that the shear strength was not only determined by surface roughness and contact area but also by the arrangement of different microstructures. These results are mainly due to the combination of mechanical interlocking and physical adhesion. Finally, the corresponding mechanical models of Al-CFRP lap joints were proposed according to the bonding mechanisms and fracture behaviors.

Influence of mechanical surface preparation methods on the bonding of southern pine and spotted gum: Tensile shear strength of lap joints

Southern pine and spotted gum are two of Australia’s most important locally produced commercial timbers. However, internationally, they are amongst the most problematic species to glue cost-effectively, especially for sawn-laminate-based structural engineered wood products, such as glulam and cross-laminated timber. This study investigated the efficacy of different pre-gluing wood surface machining preparations on the tensile shear strength of lap shear samples prepared from both species. Surface machining methods tested included planing, face milling, and sanding post-planing with 40 and 80 grit sandpaper. Wood face milling is not currently used commercially in Australia and has not previously been adequately tested on Australian commercial timbers to improve wood adhesion. Planing is currently the most common method used internationally for preparing wood surfaces for gluing. For both species, face milling with fast feed speed (45 m/min), slow cutter speed (57 m/s), and sanding treatments post-planing resulted in significantly higher tensile shear strength compared to planing for lap shear samples that had been subjected to an accelerated weathering process. Performance differences in tensile shear strength between surface machining methods are likely to be related to the effects of these machining methods on surface roughness, fibrillation, and sub-surface cell damage.

Improved mechanical properties of resistance welded joints of thermoplastic composites by versatile graphene oxide

An approach of adding graphene oxide (GO) nanosheets to enhance the joints for resistance welding glass fabric reinforced polyetherimide (GF/PEI) laminates was proposed in this study. The GO nanosheets were introduced and dispersed uniformly into the heating element (HE) of carbon fiber (CF) bundles coated PEI and the welding adhesives of PEI films in the different weight ratios. The GO nanosheets were prepared firstly by the modified Hummers method. Then their morphology and structure were also confirmed by the combination of a scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction and Raman spectrometer. The lap shear strength (LSS) obtained from single lap shear specimens and fracture morphology are reported to evaluate the optimum welding parameters, such as input power, heating time and pressure. Finally, the effect of GO on the LSS of the welded samples was studied. The results showed that the LSS of joints was increased by adding GO to the welded joint, but if it exceeded the optimal value, they were more vulnerable to damage.

Effect of adhesive thickness and adherend material with a surface roughness on lap shear strength of joints in tensile and compressive loading

ABSTRACT The lap shear strength of epoxy adhesive is determined experimentally using adhesive-bonded single lap joints with two similar adherends, aluminium alloy and steel, following ASTM standards D1002 and D905 in tensile and compressive loading. Thicknesses of the adhesive layer are 25 μm, 50 μm, 75 μm, 100 μm and 125 μm. Both tensile and compressive shear strength increase with increase in thickness of adhesive layer up to 100 μm, and it decreases at 125 μm of thickness of adhesive layer. Analysis of fractured surfaces of joints reveals that cohesive mode of failure dominated for the joint with 100 μm of thickness of adhesive layer. Compressive shear strength of the joints is higher than the tensile shear strength of joints at all the thicknesses. Further, the shear strength of joints with aluminium alloy adherends is higher than that of joints with steel adherends for both types of loading. The higher strength of aluminium alloy joints could be attributed to the surface roughness and materials of the adherends. The effect of surface roughness on shear strength is more pronounced compared to the material of adherends, i.e. aluminium alloy and steel.

Bio-based adhesive mixtures of pine tannin and different types of lignins

Tannins and lignins, which are natural phenolic compounds, are gaining substantial interest in biobased wood adhesive research. In this study, several different biobased tannin-lignin-hexamine adhesive mixtures were prepared and compared in a lap-joint shear strength test. In the first part, the suitability of different types of kraft and organosolv lignins as part of the mixture used in the production of biobased adhesives (in combination with pine tannins) were observed. It was found that biobased adhesive mixtures containing kraft lignins performed significantly better than those that contained organosolv lignins. In the second part, unmodified kraft lignins were mixed with pine tannin in different proportions, ranging from 0% to 100%. The pressing parameters were set to 150 °C for 15 min after performing oscillatory tests with a rheometer. Pure tannin adhesives performed the best, but no significant differences or a trend line were observed among adhesives containing different proportions of tannins and lignins.

Cryorolling of SAC305 solder : Microstructure analysis and shear strength of solder joint

Miniaturization of devices along with demand of higher performance in electronic packaging industries led to development of higher reliability solder alloys. Solder material must meet the requirements of high solder joint strength, better wettability, high fatigue and creep resistance in order to provide highly reliable solder joint. This work attempts to evaluate effectiveness of cryorolling in providing ultrafine grains which could lead to higher solder strength. The microstructure of bulk solder and IMC layer at interface between solder and Cu substrate, and lap joint shear strength of cryorolled commercial SAC305 solder alloy are presented here. Solder alloys were dipped in liquid nitrogen at different dipping times (0, 10, 30 and 60 minutes) prior to rolling. Cryorolling was observed to encourage grain refinement in solder with 30 min dipping gave lowest grain size of 5.88 µm, compared to 11 µm for as-cast solder. Longer dipping up to 60 minutes resulted in larger grain size and tend to be brittle with small cracks started to appear during rolling. Shear strength test showed an improved and stronger joint for SAC305 dipped in liquid nitrogen for 30 minutes compared to sample without dipping in liquid nitrogen. As a conclusion, cryorolled solder alloys had smaller grain size and this led to an improved solder joint shear strength.

Experimental study on the influences of different surface treatment processes and adhesive type on the aluminum adhesive-bonded joint strength

Surface roughness obtained from different preparation processes such as sanding, shot blasting, and sand blasting were considered in this study. The effects of surface roughness on shear strength of single-lap adhesive joint were examined. 2024-T3 aluminum sheets were cut into standard pieces and then sanded with seven sandpapers with different mesh, shot blasted for four different duration times and sandblasted under four different pressures. Pairs of prepared surfaces were attached using Araldite 2015 adhesive with high viscosity and HPL1012/HPH112 epoxy adhesive with low viscosity. Results show that the ultimate lap shear strength of the sanded samples initially increase and then decrease as surface roughness is increased. The lap joint strength continuously increases as the surface roughness of shot blasted and sand blasted samples are increased. In sanding, the optimum surface roughness is different for both high and low viscosity adhesives. However, for shot blasting and sand blasting, the optimum surface roughness is the same for both adhesive types. The maximum ultimate lap shear strength of joints for both types of adhesives obtained for sand blasting under 0.6 MPa pressure with 0.6 μm surface roughness.

Influence of freeze/thaw cycling on the mechanical performance of resistance-welded carbon fibre/polyphenylene sulphide composite joints

This study evaluates the effects of freeze/thaw cycles on the mechanical performance and failure mode of resistance-welded carbon fibre/polyphenylene sulphide composite joints. Dry and moisture-saturated joints are subjected to 1000 temperature cycles varying between –40°C and 82°C. A silane coating is applied on the stainless steel mesh heating element to improve its adhesion with the polyphenylene sulphide polymer. Results show the limited impact that freeze/thaw cycles have on the lap shear strength of joints welded without any coating on the heating element. The silane coating improves the lap shear strength by 32% when no freeze/thaw cycles are applied to the joints. This improvement of 32% reduces when joints are subjected to freeze/thaw cycles but the mechanical performance remains superior to that of joints welded using uncoated heating element. Fracture surfaces show that fibre/matrix and stainless steel/matrix interfaces are both affected by the environmental conditions although it does not translate into lower lap shear strength.