Single Lap Shear Joints Research Articles

Durability of green polyurethane adhesive bonded aluminum alloy in dry and hydrothermal ageing conditions

ABSTRACTPolyurethane (PU) adhesives were prepared from the reaction of polycaprolactone (PCL) polyols based on palm kernel oil based polyesteramide (PPKO) with an aromatic and cycloaliphatic diisocyanate. Four different formulations of PU adhesives were prepared by varying the NCO : OH ratio, in order to investigate the effects of NCO : OH ratios on adhesion strength. The adhesive strength of metal–metal bonding both in dry and hydrothermal ageing—was determined by single lap shear joint testing. The resistance to hydrolysis of the PU adhesives was determined by performing water absorption tests. The water absorption test samples suggested that the durability of the adhesives correlated to lower water absorption due to higher NCO content. The correlation between the crosslinking of the PU network and adhesive strength was also studied by performing swelling tests. The higher NCO content showed that, the higher crosslink density of PUs led to higher cohesion and adhesion strengths. PU1.7 showed optimal properties in terms of durability and resistance to hydrolysis, whereas PU2.0 revealed deterioration in durability and resistance to hydrolysis due to the presence of greater micro‐voids content in the PU2.0 matrix. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41151.

Nanofilled epoxy adhesive for structural aeronautic materials

The aim of this work was to develop new adhesive formulations based on epoxy/nanostructured carbon forms. Different types of nanofillers were dispersed into an epoxy matrix for developing toughened epoxy paste aeronautic adhesives. The reinforced adhesives were used for bonding carbon nanofilled/epoxy composite adherents. Data were also compared to the results obtained both for the unfilled adhesive and/or adherents. Tensile butt joint, and single lap joint samples were prepared to measure mechanical strength and adhesion properties of the different joint configurations. The inclusion of carbon nanofillers inside the epoxy adhesive caused a significant improvement in the bond strength of the joints, changing the failure mode of joints in single lap joint shear tests. Significant change of the bonding performance was observed as the weight fraction of carbon nano-fillers increased from 1.37 to 5wt/wt%. Adhesion between nano-reinforcements and adherents substrate was studied by means of Scanning Electron Microscopy.

Influence of Isocyanate Structures on Mechanical Performance of Aluminum Bonded with Green Polyurethane Adhesive

Polyurethane (PU) adhesives were prepared from three different polyols based on polycaprolactone (PCL)/palm kernel oil (PKO) with an aromatic and cycloaliphatic diisocyanate. The adhesives were characterized through Fourier Transformer Infrared (FTIR) spectroscopy in order to ensure the formation of urethane and the completeness of polymer reaction. The effects of NCO/OH ratios and types of diisocyanate on PU adhesive strength were investigated. The adhesive strength of metal to metal bonding was determined by single lap shear joint testing. The correlation between crosslinking of PU network and adhesive strength was also studied by performing swelling tests.

요철 형상의 스테인레스강 Z-핀으로 보강된 복합재 접합 구조물의 피로강도

Recently the authors had proposed the z-pinning patch concept to simply manufacture z-pinned composite structures at industrial production site and manufactured composite single-lap shear joint specimens using the concept. Through static tensile test on the specimens they had obtained 54~68% improvement of the joint strength. As a sequential study of it, in this study, fatigue test has performed to measure an improvement of joint strength under cyclic loading. The z-pin`s material is stainless steel and its surface was specially machined into zagged shapes and chemically corroded to increase the connection force with composite materials. Approximately 98~125% improvement of the joint strength under cyclic loading was obtained.

An infrared thermoelastic stress analysis investigation of single lap shear joints in continuous and woven carbon/fiber epoxy composites

A full-field thermoelastic stress analysis infrared method is used to study the damage initiation and progression in prepreg uni-tape and woven carbon fiber/epoxy composite single lap joints. Two loading schemes are studied to detect the damage initiation in these joints. In the first scheme the loading is monotonically increased with cyclic loading performed at the holding times. In the second scheme, the loading is increased gradually and then decreased, followed by cyclic loading at the holding time. The thermoelastic stress analysis infrared measurements show that both methods are capable of predicting the onset of damage at the bonded joint. The observed measurements indicate non self-similar crack growth or non-uniform crack extension along the bondline. Microstructural analysis is performed at the locations where damage is believed to have occurred for specimens extracted before final failure. The investigation confirms the capability of this method to capture early stages of damage in bonded joints.

Thermoelastic stress analysis for detecting and characterizing static damage initiation in composite lap shear joints

Experimental techniques using thermoelastic stress analysis (TSA) are presented to characterize static damage initiation and progression in fiber reinforced polymer (FRP) single lap shear joints. Two carbon fiber composite lap joint systems are tested: woven (fabric) laminated and uni-tape laminated orthotropic plates. The resin layer used for the bonded lap-joints is the FM300K adhesive with an approximate thickness of 10mils. Two testing methods are studied with TSA to detect damage and characterize damage severity. Several samples are removed from loading after initial cracking is suspected from observing the TSA data, and micrographic inspection is conducted to characterize and confirm the nature of their failure initiation. The proposed TSA testing schemes along with a damage index demonstrate a good ability to detect damage near the bonded edge of the joint and characterize damage severity. The damage index presented provides a distinct advantage over traditional methods such as contact gauges and acoustic emission which are unable to link detected events to the damage extent. The demonstrated TSA ability to characterize damage in lap joints is well suited for long-term fatigue tests or comparing the mechanical performance of various FRP joints.

Z-피닝 패치를 사용한 복합재 단일-겹침 전단 접합 시편의 정적강도

본 논문에서는 복합재 구조물의 제작 현장에서 쉽게 적용할 수 있는 장점을 갖는, 저자에 의하여 'Z-피닝 패치'로 명명된 새로운 Z-피닝 기술에 대하여 소개하였다. 시제작된 'Z-피닝 패치'를 사용하여 Z-핀이 박힌 복합재 단일-겹침 전단 접합시편을 성공적으로 제작하였고, 접합강도의 향상을 점검하기 위하여 시험을 수행하였다. Z-핀의 재질은 스테인레스 강이며, 복합재료와의 접합력을 향상시키기 위하여 Z-핀의 표면은 요철 형상으로 가공하였으며, 화학적으로 부식시켰다. In this paper a new concept on z-pinning technology named by authors as 'z-pinning patch' will be introduced, which advantage is easy application at manufacturing site of composite structures. Using the trial manufactured z-pinning patch, the z-pinned composite single-lap shear joint specimens were successfully manufactured and tested to check the improvement of joint strengths. The z-pin's material is stainless steel and its surface was machined as zagged shape and chemically corroded to improve joint force with composite materials.

Characterization of resistance-welded thermoplastic composite double-lap joints under static and fatigue loading

An experimental investigation of resistance welding of thermoplastic composite double lap shear (DLS) joints is presented. DLS specimens consisting of unidirectional carbon fibre/polyetheretherketone (CF/PEEK), carbon fibre/polyetherketoneketone (CF/PEKK), carbon fibre/polyetherimide (CF/PEI) and 8-harness satin weave fabric glass fibre/polyetherimide (GF/PEI) composites were resistance welded using a stainless steel mesh heating element. The welded specimens were tested under static and fatigue loadings, and the quality of the welds was examined using optical and scanning electron microscopy. Weld strengths of 53, 49, 45 and 34 MPa were obtained for CF/PEEK, CF/PEKK, CF/PEI and GF/PEI DLS joints, respectively. Indefinite fatigue lives were obtained between 20 and 30% of the ultimate static failure loads of the joints. Performances of the resistance-welded DLS and single lap shear (SLS) joints were compared. It was shown that the effect of joint geometry, that is, DLS versus SLS, on the mechanical performance of the resistance-welded joints is minimal, indicating a good resistance of welded joints to peel stresses.

Adhesion enhancement of 316L stainless steel to acrylic bone cement through nanocomposite sol–gel coating system

A nanocomposite hybrid coating was synthesised from tetraethylethoxysilane and 3-methacryloxypropyl trimethoxysilane in the presence of benzoyl peroxide as an initiator agent by sol–gel process. The AISI 316L stainless steel (SS) was coated with this coating at ambient temperature. The effect of the hybrid coating on the adhesion promotion of bone cement to SS substrate was investigated qualitatively as well as quantitatively. The adhesion tests indicated that the coated 316L SS compared with the uncoated samples induces increases of ∼450% in strength and 200% in strain by single lap joint shear test. The samples were also characterised using scanning electron microscopy, optical microscopy, Fourier transform infrared spectroscopy and small angle X-ray scattering (SAXS). The test results indicated that the coated surfaces were quite uniform and crack free. Silicon mapping and SAXS analysis of the coated samples indicated that the inorganic moieties of the hybrid (i.e. Si–O–Si) were uniformly distributed and had a particle size distribution of ∼1·5 nm. In addition, the haemocompatibility of the coated sample was investigated by clotting time test. The result of clotting time for the coated 316L SS showed an increase of 74% compared with the uncoated samples.

Application of the design of experiments procedure to the behaviour of adhesively bonded joints with plastically deformable adherends to enable further understanding of strain rate sensitivity

The study presented in this paper was carried out to investigate further the effects of strain rate on the strength of adhesively bonded single lap shear joints. Tests were carried out on two different configurations of adhesively bonded joints that were designed to exhibit different behaviours. In one configuration both adherends were made from a relatively low strength grade of aluminium such that both would exhibit significant plastic deformation prior to adhesive failure. The other configuration used one adherend that was significantly stronger such that only elastic deformation was exhibited prior to failure of the adhesive. The joint specimens were tested at several different strain rates using a servo-hydraulic test machine and the results analysed using statistical methods. To further understand the results Finite Element models of the joints were created using a Cohesive Zone Model to predict damage development and failure in the adhesive. The Design of Experiments procedure was used to study the effects of material parameters relating to both the adherends and the adhesive in the Finite Element models. The results of the testing suggested that the strength of joints formed from two adherends that exhibited plastic deformation prior to failure did not show statistically significant sensitivity to strain rate. Interpretation of the results of the Finite Element analyses suggested that the adherend yield was the main factor influencing failure load in the adhesive for joints of this type.

Environmental effects on methacrylate adhesive

In recent years, bonding techniques have been widely used to assist or even replace traditional joining techniques, such as welding and riveting. This study investigates how environmental conditions affect the mechanical behaviour of bonded joints. Analyses were carried out on single lap shear joints bonded by a two-component methacrylate-based flexible structural adhesive, extensively used in marine applications. The degradation of bonded joints in marine environment is mainly due to humidity and seawater-induced corrosion. Thus, the bonded samples were prepared for test by ageing in a climatic chamber with no applied stress (at controlled temperature and humidity) and immersion-drying cycles in a saline solution (seawater-like effect). Afterwards, tensile stress tests were performed. In order to evaluate the environment-induced degradation of the tested joints, the tensile strength of aged samples was compared with that of similar un-aged joints.

Durability of adhesively-bonded single lap–shear joints in accelerated hygrothermal exposure for automotive applications

Structural adhesives offer unique advantages in joining mixed lightweight materials in vehicle applications. One of the concerns is the potential aging during the service life, especially under exposure of hygrothermal conditions. In this study, adhesively-bonded single lap–shear (SLS) joints with thin panel sheets were exposed under various designed accelerated constant and cyclic hygrothermal environments. The residual strengths of SLS joints with different adherends were compared to assess their durability. It has been observed that the electro-galvanized steel (EGS) joints have a significant loss of the bonding strength at 80°C constant exposure, and the aluminum alloy (AL) joints exhibit a relatively stable durability in the same scenario. Moreover, the aging of SLS joints with dissimilar substrates is determined by the weaker adhesive–substrate interface, which is the adhesive–zinc interface of the EGS/AL joint under hot-wet condition. The history effect of temperature-path on residual strengths of SLS joints was also investigated. It is deduced that the durability of SLS joints under long-term exposure may be estimated by some short-term hygrothermal aging with appropriate scenarios.

Experimental study of initial strengths and hygrothermal degradation of adhesive joints between thin aluminum and steel substrates

Growing usage of lightweight materials such as Al and Mg alloys and composites in automotive body manufacturing has come to a point that bonding of dissimilar materials is a realistic problem to address. A significant issue related to the bonding of dissimilar materials is that the differences in substrate surface conditions, substrate chemical and physical properties often lead to bond failure at strength levels far less than the bond strength established by the adhesive manufacturer for a balanced joint. This research experimentally studied several important factors influencing initial shear strengths and hygrothermal degradation of adhesively-bonded single lap shear (SLS) joints. The effects of surface treatments such as lubrication and zinc coating on the substrates were first investigated. It was observed that even a very small change in the amount of lubricant applied to an aluminum alloy affected the initial shear strength. On the other hand, varying the amount of mill oil on a galvanized steel surface had little effect. Next, the comparative study of the initial joint strength between electro-galvanized (EG) steels and hot dipped galvanized (HDG) steels revealed that the two coatings exhibited no difference in terms of the initial strength. Also, various combinations of aluminum alloys and steel substrates were studied to observe the effect of substrate materials. It revealed that the strength of a dissimilar joint constructed of a strong substrate and relatively weak substrate fell below the strength of the like-material joint made of the relatively strong substrate, and was closer to the strength of the like-material joint composed of the relatively weak substrate. Ageing tests were performed on SLS joints at various temperatures with and without humidity. The shear strength barely changed after 60-days of exposure at various temperatures with room humidity, but degraded significantly at high temperature with high humidity.

Study on Thermal and Lap Shear Characteristics of Epoxy Adhesive Loaded with Metallic and Non-Metallic Particles

Influence of loading of Al2O3, Al, and Cu particles (0.5–5 μm) in an epoxy adhesive has been studied in reference to thermal stability and single lap shear joint properties of the resulting composites. The SEM studies on state of dispersion of particles in the epoxy adhesive largely reveal their homogeneous distribution in the matrix up to an optimum level of loading. The thermal stability of the neat epoxy adhesive and the epoxy-particulate composites has been studied by the TGA/DTG analysis. The thermal stability and single lap shear joint strength of epoxy-particulate composites for 10 wt% loading of Al2O3, Al, and Cu particles in the epoxy matrix show significant improvement with respect to those of the neat epoxy adhesive as well as the adhesive joint where the addition of Al gives maximum benefit in this regard. The fracture surfaces of the epoxy-particulate composites observed under SEM reveal the presence of fracture mechanisms such as shear band formation, void growth, crack deflection, crack bifurcation, and plastic shear deformation.

Measurement of adhesive shear properties by short beam shear test based on higher order beam theory

This paper refers to the measurement of the shear properties of adhesive bonding by a new beam theory using the short beam shear (SBS) test configuration. A novel higher-order sandwich beam theory has been developed to analyze the adhesive bonded beam that consists of two adhered laminates and a single layer of adhesive in between. The closed form analytical solution for the SBS test model of the adhesively bonded beam is obtained in terms of deflection and stress distribution. The present theory has been used for calculating the adhesive shear modulus from the structural compliance. The initiation of stiffness degradation for the short beam shear test model was used as the critical load value for deriving the adhesive shear strength. A finite element model is built for validating the present model, and to evaluate its suitability for measuring adhesive shear properties. The present theory shows better accuracy for measuring the shear modulus than existing theories for both thin and thick adhesive layers. The measured strength values are more accurate than those obtained from the single lap joint shear test model. This theory can be used for adhesive materials with linear elastic deformation behavior.

Quantifying the effect of porosity on the evolution of deformation and damage in Sn-based solder joints by X-ray microtomography and microstructure-based finite element modeling

The presence of reflow porosity in Sn-based solder alloys is one of the key factors affecting their reliability and mechanical performance. In this study we have used X-ray microtomography to visualize the reflow porosity in a Pb-free solder joint and to reconstruct a three-dimensional model based on the exact geometry of the pores. Interrupted shear tests and subsequent tomography were conducted to image the joint at several stages of deformation. The initial reconstructed microstructure was used as a basis for a finite element (FE) model to simulate damage and predict failure of the single lap shear joint. Sphericity analysis was conducted to verify the accuracy of the FE results. The deformation predicted by the FE simulation incorporating the ductile damage model showed very good agreement with experimental observations. The model was also able to accurately predict the crack nucleation sites and propagation path.

Cu6Sn5 and Cu3Sn lntermetallics Study in the Sn-40Pb/Cu System during Long-term Aging

Replacing Sn-Pb solder with lead-free solder is a great challenge in the electronics industry. The presented lead-free solder is Sn based and forms two intermetallic species upon reaction with the Cu substrate, namely Cu6Sn5 and Cu3Sn. The growth of Cu6Sn5 and Cu3Sn intermetallics have been investigated with respect to Sn-40Pb/Cu solder joints. The joints were aged under long-term thermal exposure using single shear lap joints and the intermetallics were observed using scanning electron microscopy. As-soldered solder joints exhibit a single Cu6Sn5 phase, however after aging a Cu3Sn layer below the Cu6Sn5 is observed to manifest. The Cu6Sn5 layer develops with a scalloped morphology, whereas the Cu in layer always develops an undulating planar shape in phase with the Cu6Sn5. The Cu6Sn5 layer begins to transform from a scalloped- to a planar-shape as aging progresses in order to minimize the interfacial energy. The intermetallic layers exhibit a linear dependence on the square root of aging time, which corresponds to diffusion-controlled growth. The activation energy for the growth of the Cu6Sn5 intermetallic layer has been determined to be 56.16 kJ/mol.

Cu6Sn5 and Cu3Sn Intermetallics Study in the Sn-40Pb/Cu System during Long-term Aging

Replacing Sn-Pb solder with lead-free solder is a great challenge in the electronics industry. The presented lead-free solder is Sn based and forms two intermetallic species upon reaction with the Cu substrate, namely Cu6Sn5 and Cu3Sn. The growth of Cu6Sn5 and Cu3Sn intermetallics have been investigated with respect to Sn-40Pb/Cu solderjoints. The joints were aged under long-term thermal exposure using single shear lap joints and the intermetallics were observed using scanning electron microscopy. As-soldered solder joints exhibit a single Cu6Sn5 phase, however after aging a Cu3Sn layer below the Cu6Sn5 is observed to manifest. The Cu6Sn5 layer develops with a scalloped morphology, whereas the Cu3Sn layer always develops an undulating planar shape in phase with the Cu6Sn5. The Cu6Sn5 layer begins to transform from a scalloped- to a planar-shape as aging progresses in order to minimize the interfacial energy. The intermetallic layers exhibit a linear dependence on the square root ofaging time, which corresponds to diffusion-controlled growth. The activation energy for the growth of the Cu6Sn5, intermetallic layer has been determined to be 56.16 kJ/mol.

Damage sensing of adhesively-bonded hybrid composite/steel joints using carbon nanotubes

Carbon nanotube networks have been used previously for in situ sensing of matrix damage in fiber-reinforced composites. In this research, the ability of carbon nanotube networks to sense and distinguish different types of damage in adhesively-bonded hybrid composite-to-metal joints is evaluated. Toward this end, conductive networks of carbon nanotubes are introduced to the composite substrate as well as the epoxy adhesive. By altering the geometry and chemically treating the steel substrate surface, different failure mechanisms of the single-lap shear joints are achieved. It is demonstrated that these failure mechanisms each possess a distinct resistance response, therefore proving the ability to not only sense failure in situ, but also to distinguish the extent and nature of damage which occurs.

A stochastic fatigue damage model for composite single lap shear joints based on Markov chains and thermoelastic stress analysis

ABSTRACTQuantitative damage detection in composite single lap joints during fatigue is difficult and not practical with many traditional experimental methods. The objective of this study is to combine a new experimental analysis method with existing stochastic models that is capable of taking the scatter inherent in composite fatigue data into account for better representation of damage evolution in single‐lap joints. This study presents a new quantitative approach where thermoelastic stress analysis (TSA), a remote sensing and non‐destructive evaluation technique, is used for in situ continuous monitoring for fatigue damage detection of Fibre Reinfoced Polymeric (FRP) S2‐glass/E733FR single‐lap joints. Image analysis algorithms are developed to capture the debonding fronts, and Markov Chain models (MCMs) are developed to capture the fatigue damage evolution in composite lap‐joints based on the experimental analysis. The TSA damage index at the last fatigue cycle is used to calibrate the MCMs, and damage predictions using the MCMs are then examined at different fatigue cycles. Methods to construct a predictive stochastic S–N curve utilizing the MCMs are discussed. The proposed IR‐TSA with MCMs is shown to be very effective in predicting the damage evolution and allowed constructing S–N curves that take the variability into account for damage in composite single‐lap joints.