Shear Strength Of Single Lap Joints Research Articles

Mechanical performance of adhesively bonded carbon fiber reinforced boron‐modified phenolic resin plastic‐titanium single‐lap joints at high temperature

AbstractThis article characterized the mechanical performance and failure mode of single‐lap joints (SLJs) of carbon fiber reinforced boron‐modified phenolic resin plastic (CF/BPR) and TC4 titanium alloy by quasi‐static tensile tests at four temperatures (25, 100, 175, and 250°C). The experimental results indicated that the shear strength of SLJs is 10.8 MPa at 25°C, which experiences monotonic drop to 80%, 42.6%, and 18.5% with temperature increase from 100 to 175°C, and to 250°C, respectively. Additionally, there was a transformation in the failure mode from composite material failure to cohesive failure in the adhesive along with the temperature increase. The intralaminar elasticities of CF/BPR were predicted using representative volume element (RVE), and the mechanical properties of three types of bondlines (i.e., the interlamination, interface of CF/BPR and the epoxy adhesive layer) were determined by both experiment and predictive methods. A finite element model taking into account the intralaminar damage of CF/BPR and the cohesive behavior of three bondlines was established. The simulated results showed good consistency with the experimental data for failure prediction, and the mechanical performance and damage propagation of SLJs at different temperatures were discussed. This research provides reference for the design and manufacture of high‐temperature bonded structures.Highlights RVE and degradation factor methods evaluate the elasticity of composite material. Four types of damage behaviors are considered in the established FE model. The SLJs exhibit single or multiple failure modes at different temperatures. The mechanical properties of SLJs severely degraded with increasing temperature.

Static Shear Strength of Single-Lap Joint Using Eggshell-Toughened Epoxy as Adhesive Agent

Eggshells are daily food waste disposed of in landfills, producing environmentalissues and an unpleasant odour. Eggshells were crushed to form eggshell powder and may be suitably applied as a filler in epoxy resins to improve their mechanical properties. The shear strength of toughened epoxy with eggshell powder (TEEP) wasstudied. Single-lap joint (SLJ) sheartests were conducted toinvestigate the shear strength of the SLJbonded with different volume fractionsof TEEP. For this purpose, the eggshells were dried and crushed into particles of size 150μm. The volume fraction of eggshell powder in the epoxy resin is 0%, 2.5%, 5%, and 10% by epoxy weight. The epoxy resin system was made of EPIKOTE Resin 828 and Hardener 651 with a mixing ratio of 5:2 by weight.The results show that the shearstrength greatly depended upon overlap lengthand filler volume fractions.The improvement was up to 72.7% and 39.9%,with the longest overlap length and 5% TEEP fraction.Hence, an overlap length of 38.1 mm and a 5% eggshell volume fraction gave the optimum shear strength of 5.045 kN.

Parametric Investigation into the Shear Strength of Adhesively Bonded Single-Lap Joints.

In this paper, the shear strength of adhesively bonded single-lap joints were experimentally and numerically investigated. Based on the validated simulation, the effects of lap length, adhesive layer thickness, adhesive layer shape, adhesive layer overflow length, and laminate lay-up on the shear strength of adhesively bonded single-lap joints were studied. The load-displacement curves and shear strength under different parameters were compared. It was shown that the shear strength of single-lap joints gradually decreases with the increase of lap length and adhesive layer thickness, which were 53.83% and 16.15%, respectively. Considering the potential condition in fabrication, the adhesive layer shape and adhesive layer overflow length were also investigated. The adhesive with normal and triangle shape owned the comparable shear strength, which was higher than the arc one. The shear strength increased by 19.37% from 18.43 MPa to 22.00 MPa with increasing the adhesive layer overflow length to 50% of lap length. It was beneficial for shear strength to increase the adhesive layer overflow length to 50% of lap length. Among the selected four lay-ups, [0]16s had the highest shear strength, which was nearly 3 times greater than the one of [90]16s. In the real process preparation, increasing the number of 0° layers, selecting the appropriate lap length and thickness of the adhesive layer, and controlling the shape and length of the adhesive layer overflow are of great help to improve the tensile shear strength of the single-lap glue joint.

Enhancement of strength of adhesive bond between wood and metal using atmospheric plasma treatment

Combinations of wood and metal are interesting hybrid composite materials, joining together the low density of wood with the stiffness and strength of metals. Different types of adhesives are used to connect wood and metal elements, but the compatibility between adhesives used and load-bearing materials must be sufficient, which often is challenging. In adhesive bonding technology, surface treatments are a crucial step in the process. In this study, an atmospheric plasma discharge was employed to enhance the adhesion strength of joints between common beech (Fagus sylvatica L.) wood, metals (steel and aluminum alloy), and four different types of adhesives. The optical properties of plasma discharges and its influence on treated substrates’ surface morphology depended on the inherent properties of the treated materials. X-ray photoelectron spectroscopy revealed the surface oxidation of all the materials after plasma treatment. Consequently, the surface free energy of all materials increased as well. The positive effect of the plasma treatment on the tensile shear strength of single-lap joints shows a high potential of atmospheric plasma treatment technology for enhancement of adhesives strength of joints combining wooden elements, wood and steel, or wood and aluminum alloys. In addition to that, expensive epoxy and polyurethane adhesives could be replaced by more affordable polyvinyl acetate and melamine-urea-formaldehyde adhesives, and still perform at equal levels if the plasma was applied prior to bonding.

Study on single-lap joints tensile properties under fire and thermal conductivity of Z-pin reinforced thermal protection composites

Quartz fiber reinforced phenolic (QFRP) resin composites were often used in thermal protection structures such as the engines and tip of missiles or rockets, but its anti-erosion performance needs to be further optimized. Z-pin technology can improve the anti-erosion performance because Z-pin effectively improved the inter-laminar shear strength of composite materials. However, it will increase the through-thickness thermal conductivity (TC), resulting in a decrease of its thermal protection performance. This paper successfully established the equation about through-thickness TC of Z-pin reinforced composites based on theoretical analysis and experimental results and tested the single-lap joints tensile strength of the samples compared with the blank and Z-pin samples under fire which characterized the interlayer performance of Z-pin reinforced thermal protection composites at high temperatures. Research showed that the through-thickness TC of the composite increases regularly with the TC and content of Z-pin, and this is because the pins act as a thermally conductive pathway. The TC increases by 13.19%, 12.34% and 12.13% when the Z-pin implantation volume fraction is 2.18%, 0.785% and 0.401%, respectively. Z-pin samples have an increase in shear strength of 63.85%, 78.97% and 88.31% compared with blank samples when the ablation time is 20s, 40s and 60s, respectively, indicating that Z-pin technology effectively could reduce the shear strength of single-lap joint with the increase of ablation time. These results prove the controllability of the through-thickness TC enhancement and effectiveness of interlayer strength by Z-pin, and guide the structural design of Z-pin reinforced thermal protection composites.

Low pressure plasma treatment of CFRP substrates for adhesive bonding: an investigation of joint durability under severe temperature-moisture conditioning

This work reports a quantitative evaluation of the aging behavior of adhesively bonded joints manufactured using a toughened epoxy adhesive applied on CFRP substrates. Low-pressure plasma (LPP) treatment was employed, adopting air and pure oxygen as process gases and varying working parameters such as power and exposure time. A preliminary testing campaign was performed under standard laboratory conditions to evaluate shear strength of single-lap joints (SLJ), comparing effectiveness of LPP treatments to a traditional mechanical abrasion of the adherends. Even at this early stage, experimental findings highlighted how this physical method provides for competitive performance over abrasion, resulting in a remarkable enhancement of the shear resistance. Four sets of LPP-treatment conditions were selected and then subjected to accelerated aging (consisting of 56 cycles of 5 h at T = 70 °C, RH>90% and 5 h at T = −40 °C each). Their behavior was compared to that of abraded joints, employed as a reference. To assess the durability of the CFRP-epoxy adhesive system under accelerated aging conditions, tensile shear strength (TSS) testing and wedge cleavage test (WT) were performed in parallel. The experimental results showed that low-pressure plasma treatment of the CFRP substrates results in increased short-term quality of the adhesive joint as well as in enhancement of its durability even under severe aging conditions.

Effect of In Addition on Microstructure, Wettability and Strength of SnCu Solder

Abstract Since the restriction on the use of Pb in solders, several Pb-free solders have been developed to replace the traditional Sn-Pb eutectic solder. The Sn-Ag-Cu series are the most commonly used lead-free solders in the electronics industry. However, during isothermal aging, the brittle Ag3Sn phase can strongly reduce the reliability of solder joints. In addition, the relatively high cost of Sn-Ag-Cu solder limited its application in the electronics industry. An attractive alternative is the Sn-0.7Cu alloy, which has shown good wettability and reasonable cost advantage compared to the Sn-Ag-Cu alloy. Despite the advantages, the melting temperature of Sn-0.7Cu alloy is approximately 10°C higher than that of Sn-Ag-Cu alloy and coarse precipitation of Cu6Sn5 during isothermal aging has been observed. This paper reports the investigation on indium addition into commercial Sn-Cu solder (SN100C) to improve its microstructure, wettability and strength performance. The solder alloys used in this work were SN100C (0.7 wt% Cu, 0.05 wt% Ni, 0.01 wt% Ge and bal. Sn) and SN100C added with 0.5, 1.0, 1.5 and 2.0wt% indium. The addition of indium is expected to refine the β-Sn grains and contribute to higher solder strength. The microstructure of bulk solder was observed using SEM equipped with EDX, while single lap joint shear strength is performed to evaluate joint strength. The wettability of solder alloy was improved with addition of In, observed via higher spreading diameter and lower wetting angle. Microstructure observation showed that In addition refined β-Sn structure, and doping of In into Cu-Sn IMC resulted in fine and rounded shape Cu-Sn-Ni-In particles. Shear strength of Sn-Cu solder joints were increased with increasing In content. The increase could be attributed to the grain structure which was substantially refined with increasing amount of In addition. The smaller grains that formed with addition of In lead to higher grain boundary density that can impede dislocation motion resulting in higher shear strength.

Abstracts

Since the restriction on the use of Pb in solders, several Pb-free solders have been developed to replace the traditional Sn-Pb eutectic solder. The Sn-Ag-Cu series are the most commonly used lead-free solders in the electronics industry. However, during isothermal aging, the brittle Ag3Sn phase can strongly reduce the reliability of solder joints. In addition, the relatively high cost of Sn-Ag-Cu solder limited its application in the electronics industry. An attractive alternative is the Sn-0.7Cu alloy, which has shown good wettability and reasonable cost advantage compared to the Sn-Ag-Cu alloy. Despite the advantages, the melting temperature of Sn-0.7Cu alloy is approximately 10°C higher than that of Sn-Ag-Cu alloy and coarse precipitation of Cu6Sn5 during isothermal aging has been observed. This paper reports the investigation on indium addition into commercial Sn-Cu solder (SN100C) to improve its microstructure, wettability and strength performance. The solder alloys used in this work were SN100C (0.7 wt% Cu, 0.05 wt% Ni, 0.01 wt% Ge and bal. Sn) and SN100C added with 0.5, 1.0, 1.5 and 2.0wt% indium. The addition of indium is expected to refine the β-Sn grains and contribute to higher solder strength. The microstructure of bulk solder was observed using SEM equipped with EDX, while single lap joint shear strength is performed to evaluate joint strength. The wettability of solder alloy was improved with addition of In, observed via higher spreading diameter and lower wetting angle. Microstructure observation showed that In addition refined β-Sn structure, and doping of In into Cu-Sn IMC resulted in fine and rounded shape Cu-Sn-Ni-In particles. Shear strength of Sn-Cu solder joints were increased with increasing In content. The increase could be attributed to the grain structure which was substantially refined with increasing amount of In addition. The smaller grains that formed with addition of In lead to higher grain boundary density that can impede dislocation motion resulting in higher shear strength.

Toughening of Epoxy Adhesives by Combined Interaction of Carbon Nanotubes and Silsesquioxanes.

The extensive use of adhesives in many structural applications in the transport industry and particularly in the aeronautic field is due to numerous advantages of bonded joints. However, still many researchers are working to enhance the mechanical properties and rheological performance of adhesives by using nanoadditives. In this study the effect of the addition of Multi-Wall Carbon Nanotubes (MWCNTs) with Polyhedral Oligomeric Silsesquioxane (POSS) compounds, either Glycidyl Oligomeric Silsesquioxanes (GPOSS) or DodecaPhenyl Oligomeric Silsesquioxanes (DPHPOSS) to Tetraglycidyl Methylene Dianiline (TGMDA) epoxy formulation, was investigated. The formulations contain neither a tougher matrix such as elastomers nor other additives typically used to provide a closer match in the coefficient of thermal expansion in order to discriminate only the effect of the addition of the above-mentioned components. Bonded aluminium single lap joints were made using both untreated and Chromic Acid Anodisation (CAA)-treated aluminium alloy T2024 adherends. The effects of the different chemical functionalities of POSS compounds, as well as the synergistic effect between the MWCNT and POSS combination on adhesion strength, were evaluated by viscosity measurement, tensile tests, Dynamic Mechanical Analysis (DMA), single lap joint shear strength tests, and morphological investigation. The best performance in the Lap Shear Strength (LSS) of the manufactured joints has been found for treated adherends bonded with epoxy adhesive containing MWCNTs and GPOSS. Carbon nanotubes have been found to play a very effective bridging function across the fracture surface of the bonded joints.

THE INFLUENCE OF LAP SIZE ON SHEAR STRENGTH OF ADHESIVE JOINTS

Adhesive joints may be used instead of forced-in joints, welded and riveted joints, soldered and twisted connections. They are characterized by a lot of advantages, thanks to them the adhesive joints are willingly used in manufacturing processes. These advantages include low price of joint, reduction of weight of the final construc tion, improvement of durability, reliability and quality and improving visual appearance. From this point of view it should be concluded that experimental tests of adhesive joints are grounded. In the paper the results of experimental tests of static shear strength of single-lap joints are presented. These joints are made with two constructive glues. The specimens made from AISI 4130 steel were glued. Their surfaces were prepared in two versions before gluing: grinded with abrasive paper by hand and cleaned by sand-blasting. The results were analyzed from variable size of the lap point of view.

Effect of adherend's rigidity on the shear strength of single lap adhesive joints

The present paper compares the tensile shear strength of single-lap joints with different adherends. Three materials were combined in the single lap joints: a carbon/epoxy laminated composite, a high elastic limit steel and the 6082-T6 aluminium alloy. The shear strength of joints was influenced by the adherend stiffness and the highest shear strengths were obtained using high stiffness adherend materials. The overlap length influenced the shear strength in different ways depending on the adherend materials. Numerical analysis concluded that the increase in the rigidity of the adherends decreases the rotation of the specimen and promotes a more uniform distribution of stresses in the glue. In joints with distinct materials, the less stiff material was found to determine the strength of the appropriate joint.

Analysis of manufacturing parameters on the shear strength of aluminium adhesive single-lap joints

An experimental and numerical investigation into the shear strength behaviour of aluminium alloy adhesive lap joints was carried out in order to understand the effect of geometrical and manufacturing parameters on the strength of adhesive bonding joints, with the aim of optimizing shear strength. The adherend material used for the experimental tests was an aluminium alloy in the form of thin sheets, and the adhesive used was a high strength epoxy. Five surface treatments were studied. The surface treatments process using sodium dichromate–sulphuric acid etch (CSA) and abrasive polishing (AP) resulted in improved joint shear strength when compared to acetone cleaning (SW), caustic etch (CE), and Tucker's reagent etch (TR). The decrease in surface roughness was found to increase the shear strength of single-lap joints. An increase in adherend thickness and overlap length was found to increase shear strength which means that an increase in joint rigidity increases its strength. A numerical analysis was developed to explain the effect of the geometrical parameters on rotation angle, stress and strain fields, and failure load. An increase in adherend thickness and overlap length decreases the joint rotation angle, reducing the plastic strain peak and therefore increasing the failure load.

Preparation of Aramid/Poly (Ethersulphone) Blends and Their Properties for Hot-Melt Type Adhesives

Abstract A wholly aromatic polyamide (aramid), prepared by the polycondensation of (3-aminophenyl) (4-aminophenyl) ether with isophthaloyl dichloride, was blended with commercially available poly (ethersulphone)s (PES and Cardo-PES) in a N-methyl-2-pyrrolidone solution. The thermal and mechanical properties of the blend films cast from NMP solution were investigated. When 80/20(w/w) aramid/Cardo-PES blend was used as an adhesive, the value of the tensile shear strength of single-lap joints had a maximum. Scanning electron microscopy (SEM) of the fracture area suggested that blending Cardo-PES enhanced some interface strength between polymer and aluminium.

Chemical interaction in the system aluminum oxide-primer-adhesive

In the present work chemical interactions between sealed chromic-acid-anodized or conversion-coated Al1100, two proprietary primers and PR-420, a polyurethane adhesive, were studied. The chemical compositions of the primers and the adhesive were determined. All the relevant combinations of substrate-primer-adhesive were evaluated, using FTIR, Auger and SIMS spectroscopies. Single lap joint shear strength of the various combinations served as an indicator to the preferred surface treatment for a sound adhesive bonding. Chromic acid anodizing with a commercial AD-6 primer gave the best results. Correlation between chemical interaction and bond strength was observed.