Epoxy Adhesive System Research Articles

Performance of optimized composition of epoxy resin adhesive used in High Friction Surface Treatment

The High Friction Surface Treatment (HFST) paving technique is widely employed in engineering practices globally, serving to enhance the long-term anti-skid performance of pavements. However, there still exist significant gaps in research regarding the modified and optimized composition and corresponding content of the polymer binding materials used in HFST, as well as the performance of the pavements laid with modified and optimized blended aggregates during service. To address these issues, this research first modified and optimized the composition ratio of traditional epoxy resin materials. Subsequently, a toughened, high-flow epoxy bonding system suitable for the maintenance of concrete pavements was prepared. Additionally, the study explored the bonding performance of this system with both the cement base surface and aggregates. The results established that the optimal ratio range for the modified epoxy adhesive system is E51 epoxy resin to curing agent to toughening agent to diluent in the proportions of 100: 30–35: 20–30: 5. The experimental group used a high-flow epoxy resin adhesive ratio of E51 epoxy resin: curing agent: toughener: diluent = 100:30:20:5. For control group 1, the ratio of epoxy resin adhesive was E51 epoxy resin: curing agent = 100:30, and for control group 2, the ratio was E44 epoxy resin: curing agent = 1:1. Compared with control groups 1 and 2, the modified epoxy system with the cement base demonstrated a 149 % increase in average pull-off strength and an 18 % increase in average shear strength. Similarly, in comparison with control groups 1 and 2, the modified epoxy system with aggregates exhibited a 174 % increase in average pull-off strength and a 541 % increase in average shear strength. Based on the pull-off and shear test results, it was ultimately determined that the dosage of modified epoxy binder for HFST mixtures should be controlled at 1.0–1.2 kg/m2, and the dosage of aggregate should be controlled at 3.3–4.3 kg/m2. These findings provide valuable insights into optimizing HFST pavement compositions for improved performance and longevity.

Multi-objective optimisation of aluminium skins and recycled/perforated PET foams sandwich panels subjected to impact loads

This work describes a methodology for the multi-objective optimisation of sandwich structures made of aluminium skins and recycled PET foams with perforated architecture. The designs are evaluated using a nonlinear finite element (FE) model validated by comparing the load, displacement and final shape of a representative sandwich panel against related experimental results. An extensive number of experiments characterise the mechanical performance of sandwich panels in pristine and perforated architected foams, the latter with perforations distributed following cubic and hexagon packing. A single lap joint test assesses the bonding between the aluminium skins and the epoxy adhesive system. Three-point bending and drop tower impact tests are performed to characterise the foams and the panels. Aluminium sheets are also tested for comparison purposes. Analysis of variance and Tukey test are used to compare the results from a statistical standpoint. The validity of the optimisation process is demonstrated through the design of sandwich panels made of hexagonal architectures of foam perforations and subjected to impact load. The sandwich panel is optimised to minimise mass and maximise the absorbed energy by using a custom routine integrated with a genetic algorithm. The results demonstrate that sandwich panels in pristine conditions provide enhanced bending performance, while panels with perforated foams have larger impact resistance. The optimisation indicates that the proposed methodology can support the design of lightweight perforated sandwich panels with superior structural performance.

Debonding of carbon fiber veil interleaved adhesively bonded GFRP joints via Joule heating

Carbon fiber veils are thin non-woven materials that enable debonding of adhesively bonded composites joints. The effects of three different carbon fiber veils on the mechanical, thermal and electrical characteristics of epoxy adhesive systems sandwiched in-between glass fiber reinforced polymer (GFRP) were examined. In comparison to the neat epoxy configurations, carbon fiber veil interleaving enhanced storage modulus, thermal diffusivity and lap shear strength (LSS) of the adhesive joints while lowering specific heat capacity (Cp) and glass transition temperature (Tg). Fourier-transform infrared spectroscopy (FTIR) analysis showed that the heated epoxy samples and composite samples made from interleaving carbon fiber veil sandwiched between two epoxy film adhesive layers at 100 °C for 1 min did not show any detectable change in their chemical structures. Surface roughness and water contact angle measurements were conducted to investigate the wettability of the GFRP adherends. Finite element coupled thermal-electric simulations and Machine Learning based solution displayed good agreement with Joule heating experiments. Thermomechanical debonding via Joule heating provided good debonding characteristics such as low force and time requirements, no fiber-tearing on the surface of the adherends and allowing selective heating of the bonded region of the joints.

Influence of Air Plasma Pretreatments on Mechanical Properties in Metal-Reinforced Laminated Wood

The use of wood-based materials in building and construction is constantly increasing as environmental aspects and sustainability gain importance. For structural applications, however, there are many examples where hybrid material systems are needed to fulfil the specific mechanical requirements of the individual application. In particular, metal reinforcements are a common solution to enhance the mechanical properties of a wooden structural element. Metal-reinforced wood components further help to reduce cross-sectional sizes of load-bearing structures, improve the attachment of masonry or other materials, enhance the seismic safety and tremor dissipation capacity, as well as the durability of the structural elements in highly humid environments and under high permanent mechanical load. A critical factor to achieve these benefits, however, is the mechanical joint between the different material classes, namely the wood and metal parts. Currently, this joint is formed using epoxy or polyurethane (PU) adhesives, the former yielding highest mechanical strengths, whereas the latter presents a compromise between mechanical and economical constraints. Regarding sustainability and economic viability, the utilization of different adhesive systems would be preferable, whereas mechanical stabilities yielded for metal-wood joints do not permit for the use of other common adhesive systems in such structural applications. This study extends previous research on the use of non-thermal air plasma pretreatments for the formation of wood-metal joints. The plasma treatments of Norway spruce [Picea abies (L.) Karst.] wood and anodized (E6/EV1) aluminum AlMgSi0.5 (6060) F22 were optimized, using water contact angle measurements to determine the effect and homogeneity of plasma treatments. The adhesive bond strengths of plasma-pretreated and untreated specimens were tested with commercial 2-component epoxy, PU, melamine-urea formaldehyde (MUF), polyvinyl acetate (PVAc), and construction adhesive glue systems. The influence of plasma treatments on the mechanical performance of the compounds was evaluated for one selected glue system via bending strength tests. The impact of the hybrid interface between metal and wood was isolated for the tests by using five-layer laminates from three wood lamellae enclosing two aluminum plates, thereby excluding the influence of congeneric wood-wood bonds. The effect of the plasma treatments is discussed based on the chemical and physical modifications of the substrates and the respective interaction mechanisms with the glue systems.

Epoxy terminated, urethane-bridged poly (ether ether ketone) as a reactive toughening agent for epoxy resins

Isocyanate terminated poly (ether ether ketone)–polymers (PEEK-NCO) were synthesized from phenolic hydroxyl functionalized poly ether ether ketone (PEEKTOH) and tolylene diisocyanate (TDI) and characterized. The PEEK-NCO polymers were then reacted with diglycidyl ether of bisphenol A (DGEBA) to form copolymers containing varying proportions of thermoplastic PEEK segments linked to DGEBA through urethane bridges. Room temperature curable, tough adhesive formulations were processed using these copolymers along with triethylenetetramine (TETA) as the curing agent. Complex viscosity, gelation time, storage modulus and loss modulus of the adhesive formulations were evaluated under isothermal conditions. Adhesive strength of the formulations was evaluated on aluminium substrates at 25 °C, 100 °C and −196 °C and the results were correlated to the composition. Cured adhesive samples were cryogenically fractured and the fracture morphologies were investigated using scanning electron microscopy. Dynamic mechanical thermal analysis was performed to understand the visco-elastic properties of the cured adhesive formulations. The PEEK- modified epoxy adhesive systems exhibited enhanced glass transition temperatures in the range of 88–90 °C vis a vis the unmodified epoxy (80 °C) and offered a broad service temperature capability from −196 °C to 100 °C.

A nonlinear viscoelastic–viscoplastic constitutive model for adhesives under creep

In this study, we consider the nonlinear viscoelastic–viscoplastic behavior of adhesive films in scarf joints. We develop a three-dimensional nonlinear model, which combines a nonlinear viscoelastic model with a viscoplastic model using the von Mises yield criterion and nonlinear kinematic hardening. We implement an iterative scheme for the viscoplastic solution and a numerical algorithm with stress correction for the combined viscoelastic–viscoplastic model into finite element analysis. The viscoelastic component of the model is calibrated using creep-recovery data from adhesive films in scarf joints. The viscoplastic parameters are calibrated from the residual strains of recovered creep tests with varying load durations. A two-dimensional form of the model shows good agreement with the three-dimensional model for the scarf joint considered in this work and is compared with experiment. The numerical results show favorable agreement with the experimental creep and recovery responses of two epoxy adhesive systems. We also discuss the contribution of nonlinear viscoelasticity and viscoplasticity to the stress/strain distribution along the adhesive center lines. Viscoplasticity tends to lower the stress concentration.

Mechanical Characterization of Core-Shell Rubber/Epoxy Polymers for Automotive Structural Adhesives as a Function of Operating Temperature

Automotive structural adhesives must show a steady toughness performance in the temperature range of −40 °C to 80 °C, considering their actual usage environments. Core-shell rubber (CSR) nanoparticles are known to enhance the toughness of epoxy systems. In this study, a CSR, pre-dispersed, diglycidyl epoxy of bisphenol A (DGEBA) mixture at 35 wt % (KDAD-7101, Kukdo Chemical, Seoul, Korea) was used as a toughener for an automotive structural epoxy adhesive system. A simple, single-component, epoxy system of DGEBA/dicyandiamide with a latent accelerator was adopted, where the CSR content of the system was controlled from 0 to 50 phr by the CSR mixture. To determine the curing conditions, we studied the curing behavior of the system by differential scanning calorimetry (DSC). Modulus variations of the cured bulk epoxies were studied using a dynamic mechanical analyzer (DMA) in the dual cantilever mode. The flexural modulus of the cured epoxies at various temperatures (−40, −10, 20, 50, and 80 °C) showed the same tendency as the DMA results, and as the flexural strength, except at 0 phr. On the other hand, the strain at break exhibited the opposite tendency to the flexural modulus. To study the adhesion behavior, we performed single-lap joint (SLJ) and impact wedge-peel (IWP) tests. As the CSR content increased, the strength of the SLJ and dynamic resistance to the cleavage of the IWP improved. In particular, the SLJ showed excellent strength at low temperatures (32.74 MPa at 50 phr @ −40 °C (i.e., an 190% improvement compared to 17.2 MPa at 0 phr @ −40 °C)), and the IWP showed excellent energy absorption at high temperatures (21.73 J at 50 phr @ 80 °C (i.e., a 976% improvement compared to 2.07 J at 0 phr @ 80 °C)). The results were discussed in relation to the changes in the properties of the bulk epoxy depending on the temperature and CSR content. The morphology of the fracture surface was also provided, which offered useful information for composition studies using the CSR/epoxy system.

Development of an Innovative Non-Destructive and Field-Oriented Method to Quantify the Bond Quality of Composite Strengthening Systems on Concrete Structures.

Over the last 30 years, structural reinforcement and retrofitting with externally bonded composite materials have proven to be efficient and cost-effective solutions to increase both the safety and the lifespan of civil engineering structures, including nuclear power plants. The effectiveness of the strengthening system highly depends on the level of adhesion between the fiber-reinforced polymer (FRP) composite material and the concrete surface. Therefore, on-site evaluation of the bond quality is critical to assess the performance and predict the durability of the system in place. The direct tension pull-off test is most commonly used to quantify the adhesion level, but this standardized method has many drawbacks. In the present study, it is proposed to evaluate the bond properties by using a nondestructive test (NDT) derived from the standard pull-off test. This innovative test enables the measurement of an interfacial “stiffness” which may be used as a bond quality criterion. This paper gives an insight into the performance of the proposed NDT method, when applied in laboratory conditions to concrete slabs reinforced with bonded pultruded carbon FRP plates (CFRP). Three different epoxy adhesive systems with a broad range of Young’s moduli were used for the specimens’ preparation, in order to vary the stiffness of the concrete/CFRP interface. The purpose was to simulate different levels of interfacial adhesion that could be observed for a single adhesive system. It was shown that the test method was able to detect differences in the interface stiffness beyond experimental uncertainties, and it should therefore enable the detection of differences in the bond quality for a given adhesive system as well. The sensitivity of the NDT was then discussed, and its detection capabilities were predicted for standard field conditions. In the last part, strain measurements were collected during the NDT, thanks to distributed optical fiber sensors (DOFS) embedded in the adhesive joints of the strengthened specimens. An analysis of the strain profiles was found to provide complementary information on the quality of the adhesive bond.

Modelling of chemical shrinkage evolution with curing degree of a filled epoxy adhesive

An epoxy adhesive system, commonly used in wind turbine blade manufacturing, is experimentally investigated with respect to its chemical shrinkage behavior to show the shrinkage evolution within rotor blade production related process conditions. Therefore, a new test configuration is set up to record the resulting chemical shrinkage of the adhesive at cross-linking temperatures ranging from 20°C to 90°C. The respective conversion evolution is simulated under several temperature conditions through a curing kinetics model. This is generated with state of the art formulations, implementing test results from a differential scanning calorimeter (DSC). Moreover, the transformation of the curing degree to the corresponding glass transition temperature (Tg ) is performed through an experimentally based Di-Benedetto curve-fitting. By the combination of curing kinetics and chemical shrinkage test data, a model for the temperature and conversion dependant chemical shrinkage evolution during cure is developed. This is applied to a realistic curing cycle for adhesive materials in rotor blade production.

Internal stress analysis of epoxy adhesively‐boned joints based on their thermomechanical properties at cryogenic temperature

AbstractInternal stress analysis is essential to structural design of materials applied in cryogenic engineering. In this contribution, thermomechanical properties including dynamic thermomechanical properties and thermal expansion behavior of four epoxy resins, namely the polyurethane modified epoxy resin (PUE), diglycidyl ether of bisphenol A (DGEBA), tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) and triglycidyl‐p‐aminophenol (TGPAP) were studied by dynamic thermomechanical analysis. Internal stress of the epoxy layer in the bonded joint was calculated based on the thermomechanical properties. Meanwhile, the structure‐cryogenic property relationship of epoxy resins were investigated. Results demonstrate that internal stress in the four epoxies bonded joints is 6 ~ 21 MPa at −150°C, and is positively correlated with the average thermal expansion coefficient (CTE) of epoxy resins. TGDDM and TGPAP showed higher retention of lap shear strength both at −196°C and after temperature cycling due to their lower CTE. Morphology of the fractured surface of bonded joints demonstrated that internal stress is responsible for the severe interface failure at −196°C. It reveals that selection of epoxy resins with low CTE is beneficial for designing high‐performance epoxy adhesive systems served at cryogenic temperature.

Effect of the in-situ polymerized polyurethane on laminated epoxy adhesive / aramid fabrics composites

In order to avoid the high brittleness of epoxy resin and the low peeling strength of its laminated composite, polyurethane was synthesized by in-situ polymerization in epoxy adhesive system. The results of IR, SEM and mechanical properties test showed that the peel strength and shear strength of laminated epoxy adhesive / aramid fabrics composites reached the optimum value when the molar ratio of NCO/OH was 1.2, the content of MoCA curing agent was 1.5% and the content of polyurethane prepolymer was 20%. The brittleness of epoxy resin was reduced to a certain degree, and the bonding properties of epoxy adhesive/aramid fabrics composites were improved.

STRENGTH ANALYSIS OF GLUED-IN STEEL RODS WITH DIFFERENT LOCATIONS IN CLT PANELS CROSS SECTION

New types of wood based building materials to which the CLT refers require an accurate evaluation of the strength of varioustypes of connections. CLT panels connections with glued-in steel rods are of interest due to the possibility of creating quickmounted and rigid joints in the factory. Since the CLT have the structure of the perpendicular orientated boards in adjacentlayers, the strength and behaviour of the pasted rods is difficult to predict. The purpose of this study was to establish thestrength of the glued-in rods by pull-pull tests with different locations relative to the boards layers in the cross-section of theCLT panel. Diameter of all considered steel rods was smaller than thick of timber planks 30 mm in 5-lyers CLT specimenswithout gaps and stress relieves. Anchored length of rods in all specimens was 100 mm by using two component epoxy adhesive system.

Characterization of aluminum alloy-epoxy bonded joints with nanofibers obtained by electrospinning

ABSTRACTIn previous works, the authors showed that nylon nanofibers in the form of a random mat (nanomat) obtained by electrospinning can be used in bonded joints, where they may also work as an adhesive carrier. In those works, the setup of the bonding procedure started from a low-viscosity epoxy resin for hand layup in order to facilitate wetting of the nanomat, then a medium viscosity, two-component, unfilled epoxy adhesive was employed as an intermediate development step towards the addition of the nanomat to a high-viscosity, high strength, two-component epoxy adhesive system. The present work is therefore aimed at analyzing the performance of an epoxy adhesive for structural bonding, modified with the addition of a nylon nanomat generated by electrospinning. The adhesive is mixed and air bubbles are evacuated, then the nanomat is immersed in the adhesive, gently squeezed through two adjacent drums, counter-rotating at a given distance, in order to eliminate excess adhesive and to calibrate the wet nanomat thickness. The wet nanomat strip is finally placed between AA 6082-T4 adherents and let to consolidate to obtain Double Cantilever Beam (DCB) bonded specimens. Fracture tests are performed and the mode-I fracture toughness with and without the nanomat is compared.

Thermokinetics behavior of epoxy adhesive reinforced with low viscous aliphatic reactive diluent and nano-fillers

The current study reports the effect of low viscous aliphatic reactive diluent (RD), MWCNT and VGCF on the curing kinetics of amine cured epoxy adhesive system employing non-isothermal differential scanning calorimetric (DSC) technique. Non-isothermal DSC thermograms of epoxy adhesive were studied at various heating rates: 5, 10 and 15 °C/min. The decrease in the exothermic peak height with the introduction of MWCNTs and VGCFs was taken as proof of the acceleration effect of nano-fillers on the epoxy-amine curing reaction. Also, increased T onset , T P and ΔH curs values were observed for epoxy/RD adhesive system at all heating rates. The value of activation energy (E a ) was determined using Kissinger and Flynn-Wall-Ozawa methods. Experimental results showed that the addition of 10 wt% RD increased the E a from 60 to 63 kJ/mol on account of the reduced viscosity, allowing better contact of resin with the curing agent. Furthermore, MWCNTs have an accelerating effect on the cure kinetics that does not change the autocatalytic cure reaction mechanism of epoxy resin. It was also found that the addition of MWCNT and VGCF decreases the overall degree of conversion, as evident with lower ΔH cure and E a of the cured adhesive when compared with epoxy/RD system. The dependency of E a on degree of conversion ranging from α =0.1 to 0.9was also investigated. The two normalized functions y(α) and z(α) were also considered in order to study the complex curing mechanism. The kinetic parameters m, n and lnA were obtained by using two parameter autocatalytic Sestak-Berggren model. The curves revealed good agreement between experimentally determined and theoretically obtained MWCNT/VGCF reinforced epoxy adhesive systems.

Aligned multi-walled carbon nanotubes (MWCNT) and vapor grown carbon fibers (VGCF) reinforced epoxy adhesive for thermal conductivity applications

Present study deals with the development of aligned multi-walled carbon nanotubes (MWCNT) and vapour grown carbon fibers (VGCF) reinforced epoxy adhesive system used as an alternative to Pb/Sn soldering element. The alignment of MWCNTs was carried out in a specific designed instrument exerting of an external electric field. Solution casting technique was used for the fabrication of epoxy adhesive system incorporated with aligned MWCNT and VGCF. Scanning electron microscopy and Atomic force microscopy was carried out to determine the degree of alignment of MWCNTs. Owing to the formation of continuous path for the flow of electrons, 3 wt% of aligned MWCNT with 3 wt% of VGCF reinforced epoxy adhesive achieved about five orders of magnitude higher in the thermal conductivity compared to pure epoxy. Further, the experimental results showed that the shear strength of epoxy/3% MWCNT/3% VGCF adhesive system was 112% higher than the strength of pure polymer, emphasizing the advantages of aligned MWCNT on stiffness and strength. Dynamic Mechanical Analysis and Thermo-gravimetric analysis was carried out to study the thermo-mechanical and thermal degradation behaviour of epoxy adhesive formulations.

Synergistic effect of hybrid graphene and boron nitride on the cure kinetics and thermal conductivity of epoxy adhesives

In the present study, the synergistic effect of hybrid boron nitride (BN) with graphene on the thermal conductivity of epoxy adhesives has been reported. Graphene was prepared by chemical reduction of graphite oxide (GO) in a mixture of concentrated H2SO4/H3PO4 acid. The particle size distribution of GO was found to be ~10 μm and a low contact angle of 54° with water indicated a hydrophilic surface. The structure of prepared graphene was characterized by Fourier transform infrared (FTIR), X‐ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM). The thermal conductivity of adhesives was measured using guarded hot plate technique. Test results indicated an improvement in the thermal conductivity up to 1.65 W/mK, which was about ninefold increase over pristine epoxy. Mechanical properties of different epoxy formulations were also measured employing lap shear test. The surface characterization of different epoxy adhesive systems was characterized through XRD, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies. Fourier transform infrared also served to determine the nature of interactions between filler particles and epoxy resin. Non‐isothermal differential scanning calorimetric (DSC) technique was used to investigate the effects of graphene and BN particles on the cure kinetics and cross‐linking reaction of epoxy cured with amine curing agent. The Kissinger equation, the model‐free isoconversional Flynn–Wall–Ozawa method and the Ozawa model were used to analyze the kinetic parameter. Copyright © 2017 John Wiley & Sons, Ltd.

Study on metal decorated oxidized multiwalled carbon nanotube (MWCNT) - epoxy adhesive for thermal conductivity applications

In this work, an effort has been made to develop a new type of complex conductive adhesive filled with silver decorated multi-walled carbon nanotubes (Ag-MWCNT). MWCNTs have been modified using N,N-dimethyl formamide (DMF) as a reducing agent and silver nanoparticles (Ag-NPs) has been homogeneously decorated against the surface. Fourier transform infra-red spectroscopy (FTIR) and Raman spectroscopy concluded that carboxylic groups were anchored to the surface of nanotubes. X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS) confirmed that Ag-NPs were formed and uniformly deposited onto the surface of carboxylic functionalized MWCNT. Test results indicated an improvement in the thermal conductivity up to 0.88 W/mK, which was about four-fold increase over pristine epoxy. The curing kinetics of Ag-MWCNTs reinforced epoxy adhesive system was also studied using non-isothermal differential scanning calorimetric (DSC) technique. The activation energy obtained by Kissinger’s method was reduced from 57.2 to 54 kJ/mol with an addition of 0.5 wt% of Ag-MWCNT within unmodified epoxy. Lap shear strength of the adhesive containing 0.5 wt% of Ag-MWCNT was higher than the pristine polymer thus confirming reinforcing effect of Ag-MWCNT in conductivity applications.

A logistic kinetic model for isothermal and nonisothermal cure reactions of thermosetting polymers

ABSTRACTA model describing the low‐temperature crystallization kinetics observed for thermoplastic polymers from the melt by differential scanning calorimetry (DSC) was shown to accurately predict the cooling curves as a function of time and temperature. The model was successful for treating data for several cooling rates as well as for isothermal DSC data. In this article, we extended the model to cure reactions of thermosetting polymers. The parameters representing lower and upper exotherm reference temperatures in crystallization events have a different meaning for curing events. Thus, the model was modified to account for this change of context. The new model was tested for exothermic reactions of a Hysol® FP4527 epoxy adhesive system using data from DSC ramp heating experiments at several heating rates and also from isothermal experiments. Good fits were obtained for all the varied experimental conditions. The model made use of three fitting parameters with physical significance: a lower critical temperature (Tc) an activation energy (Eb), and a reaction order (τ + 1). Additionally, to complete the kinetic fitting, the dependence of the time to reach the reaction peak maximum for isothermal cure was considered. That dependence was found to follow a more simple model which is formally equivalent to that observed in isothermal crystallization, and which makes use of two parameters related to the limits of the temperature range in which the polymerization may occur. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40670.

Non Destructive Evaluation of Degradation in Bond Line of Glass Fiber Reinforced Polymer Composite Adhesive Lap Joints

A critical issue in using adhesives for structural joints is the assessment of integrity and reliability of these joints in service. One of the factors limiting the wide spread use of adhesives for structural bonding in industries is the lack of reliable non destructive testing methods to evaluate the bonded joints. Joining of fiber reinforced polymer (GFRP) composite materials by adhesive bonding has to take into account factors such as the adopted bonding process, the interface properties and the control of the adhesive bond line thickness. In this paper, results of experimental investigations on the non destructive evaluation (NDE) of single lap bonded joints made of glass fiber reinforced epoxy matrix composite laminates are presented. Unidirectional glass fiber reinforced plastic substrates were joined using a two part epoxy adhesive system. Specimens with varied bond quality were prepared adding different proportions of poly vinyl alcohol (PVA) to the epoxy hardener mixture. The bonded area of the s...

Analysis and design of adhesively bonded joints for fatigue and fracture loading: a fracture-mechanics approach

An experimental–computational fracture-mechanics approach for the analysis and design of structural adhesive joints under static loading is demonstrated by predicting the ultimate fracture load of cracked lap shear and single lap shear aluminum and steel joints bonded using a highly toughened epoxy adhesive. The predictions are then compared with measured values. The effects of spew fillet, adhesive thickness, and surface roughness on the quasi-static strength of the joints are also discussed. This fracture-mechanics approach is extended to characterize the fatigue threshold and crack growth behavior of a toughened epoxy adhesive system for design purposes. The effects of the mode ratio of loading, adhesive thickness, substrate modulus, spew fillet, and surface roughness on the fatigue threshold and crack growth rates are considered. A finite element model is developed to both explain the experimental results and to predict how a change in an adhesive system affects the fatigue performance of the bonded joint.