The effect of adhesive thickness on tensile and shear strength of polyimide adhesive

The effect of adhesive thickness on tensile and shear strength of a polyimide adhesive has been investigated. Tensile and shear tests were carried out using butt and single lap joints. Commercially available polyimide (Skybond 703) was used as adhesive and aluminum alloy (5052-H34) was used as adherends. The tensile strength of the butt joints decreased with increasing adhesive thickness. In contrast, adhesive thickness did not seem to affect the shear strength of single lap joints. The fabricated joints using the polyimide adhesive failed in an interfacial manner regardless of adhesive thickness. The linear elastic stress analysis using a finite element method (FEM) indicates that the normal stress concentrated at the interface between the adherend and the adhesive. The FEM analysis considering the interfacial stress well explains the effect of adhesive thickness on the joint strength.     

A Method of Estimating the Strength of Adhesive Bonded Joints of Metals

The strength of adhesive bonded joints is investigated both analytically and experimentally. The deformed states of lap joints under tensile shear loading are analysed by the finite element method on the assumption of elastic deformation. A method of using the adhesive strength law is proposed to estimate the joint strength. The adhesive strength law is experimentally determined by subjecting butt joints of two thin-walled tubes to combined axial load and torsion. The strength of lap joints is determined by adopting the adhesive strength law to the adhering interface as well as the strength law of adherend and adhesive resin. The calculated strain distribution and strength of the joints are compared with the experimental results. The effects of the joint configurations on the deformation and strength are discussed. It is shown that the proposed method is useful to predict the joint strength.     

A Method of Estimating the Strength of Adhesive Bonded Joints of Metals

The strength of adhesive bonded joints is investigated both analytically and experimentally. The deformed states of lap joints under tensile shear loading are analysed by the finite element method on the assumption of elastic deformation. A method of using the adhesive strength law is proposed to estimate the joint strength. The adhesive strength law is experimentally determined by subjecting butt joints of two thin-walled tubes to combined axial load and torsion. The strength of lap joints is determined by adopting the adhesive strength law to the adhering interface as well as the strength law of adherend and adhesive resin. The calculated strain distribution and strength of the joints are compared with the experimental results. The effects of the joint configurations on the deformation and strength are discussed. It is shown that the proposed method is useful to predict the joint strength.     

Effect of Temperature on the Joints Strength of an Automotive Polyurethane Adhesive

In this paper, the performance of an automotive polyurethane adhesive was studied through adhesive joints tests. Butt joints and single lap joints were fabricated and tested at seven temperature measuring points (TMPs). It is shown that both the tensile strength and lap shear strength decrease with the increasing of temperature. Quadratic polynomial expression obtained by the least square method can represent the tensile and lap shear strength as a function of temperature very well. ?40°C, 0°C, and 90°C were selected as the most ideal TMPs for this adhesive through the comparison of the residual sums of squares of 35 fitting curves with different combination of TMPs. Scarf joints with adhesive angles of 60° and 30° were fabricated and tested at ?40°C, 0°C, and 90°C. It also showed a decrease in joint strength with the increasing temperature. Joint strength as a function of adhesive angle is presented. It was found to closely follow a linear behaviour. A three-dimensional surface, consisting of temperature, adhesive angle, and joint strength, is presented finally to facilitate the design of automotive bonding structures.     

Experimental investigation into the effect of DC glow discharge pretreatment of HDPE on tensile lap shear strength

The present investigation aims to optimise the process parameters of DC glow discharge treatment through air in terms of discharge power and time of exposure for attaining best adhesive joint of high-density polyethylene (HDPE) to mild steel. The as- received and DC glow discharge exposed HDPE surfaces have been characterised by energy dispersive spectra (EDS). It is observed that with increasing power level up to 13 W, tensile lap shear strength of adhesive (Araldite AY 105) joint of HDPE to mild steel increases and then decreases. At 13 W power level, joint strength increases up to 120 s of exposure and then decreases. At the optimised condition for the surface modification, the effect of two different adhesives Araldite AY 105 and Araldite 2011 on the strength of polymer to mild steel, polymer to polymer and mild steel to mild steel joints have been examined. It is observed that tensile lap shear strength of HDPE–HDPE joint and HDPE–mild steel joint does not change with the change of adhesive and this could be possible as initiation of fracture takes place from subsurface layer of the polymer. This is confirmed by studies under optical microscopy and EDS, which shows when the polymer has been modified by exposure under glow discharge the failure is observed to initiate from subsurface layer of the HDPE, then within the adhesive cohesively and thereafter in the mild steel to adhesive interface.     

Tensile Strength of Joints Bonded With a Nano-particle-Reinforced Adhesive

In order to improve the tensile lap shear strength of adhesively bonded joints, nano-particles were dispersed in the adhesive using a 3-roll mill. The dispersion states of nano-particles in the epoxy adhesive were observed with TEM (Transmission Electron Microscopy) with respect to the mixing conditions, and the effect of nano-particles on the mechanical properties of the adhesive was measured with respect to dispersion state and weight content of nano-particles. Also the static tensile load capability of the adhesively bonded double lap joints composed of uni-directional glass/epoxy composite and nano-particle-reinforced epoxy adhesive was investigated to assess the effect of nano-particles on the lap shear strength of the joint. From the experimental and FE analysis results, it was found that the nano-particles in the adhesive improved the mechanical properties of the adhesive. Also the increased failure strain and the reduced CTE (coefficient of thermal expansion) of the nano-particle-reinforced adhesive improved the lap shear strength of adhesively bonded joints.     

Glass/epoxy composites and aluminium alloy joint using Kevlar® intermediate layer and nanoclay-reinforced epoxy adhesive

Adhesive lap joint between glass fibre/epoxy composites and aluminium alloy (2014 T4) was prepared by an in situ moulding process using a matched die mould. The surface of aluminium alloy was treated with chromic acid before adhesive bonding. Lap shear strength and fatigue life were evaluated in tensile mode and tension–compression mode (at 40% of lap shear load of adhesive joint), respectively. Knurling on the surface of aluminium alloy improved the lap shear strength of the adhesive joint but did not influence the fatigue life of the same. Lap shear strength and fatigue life of adhesive joint made with neat epoxy adhesive and reinforcement of an intermediate layer of Kevlar^® between glass/epoxy composite and aluminium alloy were observed to be 0.44?kg/mm² and 3.6?×?10⁵ cycles, respectively. In another case, lap shear strength and fatigue life of similar type of adhesive joint made from nanoclay (Cloisite 30B)-reinforced epoxy adhesive and without reinforcement of an intermediate layer of Kevlar^® were observed to be 0.38?kg/mm² and 2.3?×?10⁵ cycles, respectively. Whereas, lap shear strength and fatigue life of adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar^® were 0.48?kg/mm² and 3.9?×?10⁵ cycles, respectively. Therefore, adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar^® was the best.     

Effect of bonding defects on shear strength in tension of lap joints having brittle adhesives

In this paper we examine how the joint strength of lap joints containing a brittle adhesive may be affected by partial removal of adhesive from the bonded area. It is found that the shear strength in tension of a lap joint specimen is governed essentially by the leading edges of the joint and not by the bonded area.     

单搭接接头承载能力与搭接长度关系定量描述

为了研究单搭接接头承载能力与搭接长度的定量关系,对不同搭接长度的单搭接接头进行了有限元分析,得到了单搭接接头承载能力与搭接长度的关系曲线图。并用曲线拟和的方法定量描述了接头承载能力与搭接长度关系。实验结果表明接头承载能力随搭接长度的增加而增长。接头承载能力与搭接长度为非线性关系,也验证了这种定量描述方法的合理性。     

Synthesis and properties of allyloxyethyl 2-cyanoacrylate adhesive

Allyloxyethyl 2-cyanoacrylate monomer was synthesized and characterized for the first time. It was found that this monomer retains the typical properties of cyanoacrylate adhesives such as fast setting time at room temperature, adhesion to most materials, and high strength of bonded joints. Because of its long ester group and the reactive allyl group, this cyanoacrylate monomer produces adhesive bonds which have improved elasticity and heat resistance. IR and DSC studies showed crosslinking of the adhesive layer when subjected to elevated temperature, which explains the increased tensile shear strength of steel bonded joints. It was found that allyloxyethyl 2-cyanoacrylate can also be used as a crosslinking component for cyanoacrylate adhesives, based on ethyl 2-cyanoacrylate. Less than 10% of allyloxyethyl 2-cyanoacrylate in the mixture is needed for increasing, over three times, the tensile shear strength of the adhesive joint after ageing at 100°C.     

The effects of Al surface treatment,adhesive thickness and microcapsule inclusion on the shear strength of bonded joints

The influences of various Al surface treatments, adhesive thicknesses as well as the incorporation of synthesized microcapsules into epoxy adhesive on the shear strength of adhesive/ Al joints have been investigated using lap-shear tensile tests. First, the influence of adhesive thickness on the shear strength of joints has been presented. Then, the effects of various Al surface treatments on the surface roughness of Al and shear strength of joint have been researched. Atomic force microscopy was used to study the Al surface morphologies and textures. Finally the few micron-sized polymeric microcapsules were synthesized and the shear performances of microcapsule filled epoxy adhesives were inspected. It was observed that the HCl acid based etching increased both micro-roughness and nano-texture of the Al surface and led to the peak shear strength. Moreover, HCl-nitric acid treatment offered the maximum value for the cohesive failure. Capsule inclusions into the adhesive displayed different influences on the joint shear performances depending on the capsule morphology and the surface treatment of Al.     

Bio-adhesion evaluation of a chitosan-based bone bio-adhesive

Conventional treatment of complex fractures includes the use of plates and nails, which may compromise the affected limb's functionality. Previous studies have demonstrated promising results through chemical, mechanical, and cytotoxicity tests of a chitosan-based adhesive—proposed as a new method to bond high energy fractures—in dry environments with adequate adhesion, malleability, and biocompatibility. In this study, we focused on performing an evaluation of bio-adhesives’ mechanical properties and bone-adhesive joint using two chitosan-based formulations (with and without a cross-linking agent). The texture profile analysis determined adhesive properties, such as cohesiveness, adhesiveness, hardness, and resilience at different cure times. Bone-adhesive joint was evaluated according to the tensile bond strength test and shear bond strength test. Fracture toughness and cohesive strength were calculated through a rigid double cantilever beam test at mode I failure. Bone-adhesive joints were tested in two environments: dry and submersed in water at 37 °C for 1, 6, and 24 h (curing time), an approximation of surgery conditions. The experimental results showed an incremental of adhesiveness and hardness of the cross-linked adhesive during the first 15 min, which was determined as the usage time to spread on the bone fracture. The joint interaction between the adhesive and bone surfaces was studied; chitosan-based formulations showed an adhesive joint failure under dry conditions in most of the cases. However, this behavior changed under aqueous conditions, presenting cohesive failures. Under aqueous conditions, cross-linked bone-adhesive presented an augmented tensile bond strength up to 0.024 ± 0.0036 MPa, a shear bond strength up to 0.031 ± 0.0069 MPa, and fracture toughness of 2.38 ± 0.54 J/m² was observed with a cure time of 24 h. Finally, the presence of the cross-linking agent in the cross-linked bio-adhesive reduced the sensitivity of the adhesive to water; a promising finding that should be explored in future studies.     

Numerical study of lap joints with composite adhesives and composite adherends subjected to in-plane and transverse loads

In this paper, single lap joints for joining fibre composites were modeled and a three-dimensional finite element method was used to study the joint strength under in-plane tensile and out-of-plane loadings. The behaviour of all the members was assumed to be linear elastic. The adherends were considered to be orthotropic materials while the adhesive could be neat resin or reinforced one. The largest values of shear and peel stresses occurred near the ends of the adhesive region, as expected. The values and the rate of variation in peel stress was more than that of shear stress. By changing the properties and behaviour of adhesive from neat epoxy (isotropic) to fibre composite adhesive (orthotropic) and with various fibre volume fractions of glass fibre, the ultimate bond strength increased as the fibre volume fraction increased, in both tensile and transverse loadings. Also, changing the orientation of fibres in the adhesive region with respect to the global axes influenced the bond strength.     

An adhesive joint strength evaluation method and its application in mechanical engineering

Traditional material joining techniques are facing enormous challenges due to the widely use of new materials in engineering. Therefore, the application of bonding technique in engineering becomes more and more important. In order to facilitate evaluation of the adhesive joint strength, a simple and efficient adhesive joint strength evaluation method which applies to engineering application was proposed in this paper. Tensile and shear stresses were selected as the main research objects in the method considering the complex working conditions that many adhesive structures may face in engineering. Butt joint, single-lap joint and several groups of scarf-joint specimens with different adhesive angles were fabricated. Numerous repetitive tensile tests were conducted to determine the adhesive failure stresses under different conditions. The adhesive failure stress envelope was fitted based on the experimental data and the evaluation method of adhesive joint strength was developed in detail. Finally, verification experiments were designed to determine the validity and reliability of the evaluation method.     

Strength of epoxy adhesive-bonded stainless-steel joints

The strength of stainless-steel joints bonded with two epoxy adhesives was investigated. The experimental programme included tests on single-lap and butt joints, as well as thick-adherend and napkin ring shear tests. Results suggested that the tensile and shear strengths of the epoxy adhesives were quite similar. However, finite element (FE) analyses raised doubts on the true adhesive strengths, due to the complex stress state in joint tests and pressure-dependent adhesive behaviour. In spite of some uncertainties, FE analyses showed that failure could be fairly well predicted by a maximum shear strain criterion.     

Thermal characteristics of tubular single lap adhesive joints under axial loads

When an adhesive joint is exposed to high environmental temperature, the tensile load capability of the adhesive joint decreases because both the elastic modulus and failure strength of the adhesive decrease. The thermo-mechanical properties of a structural adhesive can be improved by addition of fillers to the adhesive. In this paper, the elastic modulus and failure strength of adhesives as well as the tensile load capability of tubular single lap adhesive joints were experimentally and theoretically investigated with respect to the volume fraction of filler (alumina) and the environmental temperature. Also the tensile modulus of the filler containing epoxy adhesive was predicted using a new equation which considers filler shape, filler content, and environmental temperature. The tensile load capability of the adhesive joint was predicted by using the effective strain obtained from the finite element analysis and a new failure model, from which the relation between the bond length and the crack length was developed with respect to the volume fraction of filler.     

环氧/多巯基型无色透明胶粘剂的研制

采用自制多巯基固化剂与E-51环氧树脂制备了一种环氧/多巯基型无色透明胶粘剂,对其拉伸剪切强度、黏度、紫外-可见光透过率等性能进行了研究,并在相同条件下与使用进口固化剂的胶粘剂性能进行了对比。结果表明,随着固化温度升高,2种胶粘剂拉伸剪切强度均不断提高,在固化温度达到110℃时拉伸剪切强度均达到最大,随后开始下降。随温度升高,2种胶粘剂黏度均不断下降。紫外-可见光透过率的测试表明,固化温度对进口胶粘剂的透明度影响很大,80℃透过率就明显下降。固化温度在80℃内,自制胶粘剂的紫外-可见光透过率变化不大。在此环氧体系中,使用自制固化剂的胶粘剂在耐温性方面具有一定优势。     

Hygrothermal Properties of Adhesively Bonded Joints and Their Correlation with Bulk Adhesive Properties

The combined effects of heat (50[ddot]C) and humidity (95% R.H.) on the lap shear and T-peel strengths of 120[ddot]C, 150[ddot]C and 215[ddot]C service epoxy film adhesives have been characterized. Experimental results have indicated that effects of hygrothermal conditioning on lap shear and peel properties vary with exposure time and final testing temperatures and type of adhesive tested. In the cases where cohesive failure was observed in the shear and peel specimens, a correlation could be established between the bulk properties of the adhesives (tensile strength and elongation) and their adhesively bonded joint properties (shear and peel). When testing was carried out at room temperature, a general correlation between the tensile elongation and T-peel or shear could be obtained. At below freezing temperatures, lap shear strength seemed to be correlated with bulk tensile strength while peel correlated with bulk tensile elongation. At elevated temperatures, the relative contributions of bulk strength and elongation were the decisive factors as far as shear and peel strengths are concerned.     

Comparison of fracture behavior between acrylic and epoxy adhesives

An experimental study was conducted on the strength of adhesively bonded steel joints, prepared epoxy and acrylic adhesives. At first, to obtain strength characteristics of these adhesives under uniform stress distributions in the adhesive layer, tensile tests for butt, scarf and torsional test for butt joints with thin-wall tube were conducted. Based on the above strength data, the fracture envelope in the normal stress-shear stress plane for the acrylic adhesive was compared with that for the epoxy adhesive. Furthermore, for the epoxy and acrylic adhesives, the effect of stress triaxiality parameter on the failure stress was also investigated. From those comparison, it was found that the effect of stress tri-axiality in the adhesive layer on the joint strength with the epoxy adhesive differed from that with the acrylic adhesive. Fracture toughness tests were then conducted under mode l loading using double cantilever beam (DCB) specimens with the epoxy and acrylic adhesives. The results of the fracture toughness tests revealed continuous crack propagation for the acrylic adhesive, whereas stick-slip type propagation for the epoxy one. Finally, lap shear tests were conducted using lap joints bonded by the epoxy and acrylic adhesives with several lap lengths. The results of the lap shear tests indicated that the shear strength with the epoxy adhesive rapidly decreases with increasing lap length, whereas the shear strength with the acrylic adhesive decreases gently with increasing the lap length.     

Analysis of tubular adhesive joints with a functionally modulus graded bondline subjected to axial loads

The strength and lifetime of adhesively bonded joints can be significantly improved by reducing the stress concentration at the ends of overlap and distributing the stresses uniformly over the entire bondline. The ideal way of achieving this is by employing a modulus graded bondline adhesive. This study presents a theoretical framework for the stress analysis of adhesively bonded tubular lap joint based on a variational principle which minimizes the complementary energy of the bonded system. The joint consists of similar or dissimilar adherends and a functionally modulus graded bondline (FMGB) adhesive. The varying modulus of the adhesive along the bondlength is expressed by suitable functions which are smooth and continuous. The axisymmetric elastic analysis reveals that the peel and shear stress peaks in the FMGB are much smaller and the stress distribution is more uniform along its length than those of mono-modulus bondline (MMB) adhesive joints under the same axial tensile load. A parametric evaluation has been conducted by varying the material and geometric properties of the joint in order to study their effect on stress distribution in the bondline. Furthermore, the results suggest that the peel and shear strengths can be optimized by spatially controlling the modulus of the adhesive.