Effect Of Adhesive Thickness Research Articles

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

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

Non-Monotonous Effect of Adhesive Thickness on The Dynamic Stiffness of Adhesive Butt Joint

This research investigated the effect of the thickness of adhesive to the stiffness (Young’s modulus) of adhesive butt joint at high strain rate loading. A split Hopkinson pressure bar (SHPB) test is used to obtain the stress-strain response of join specimen at strain rate of 530±10 s-1. The joint is composed of aluminum adherend bonded by epoxy adhesive with 0.5, 1, 2, and 3 millimeter of thickness variation. The results show that the joint deformed elastically and the stiffness increases with the increase of adhesive thickness. However, the rate at which the stiffness increases with thickness decreases at thick adhesive layer. The facts of this research are important for the improvement of the crashworthiness of structure such as automobile structures.

Influence of sample dimensions on single lap joints: effect of interactions between parameters

ABSTRACT The main aim is to understand the effect of adhesive thickness, length and width, and their interactions for highly flexible adhesives on single lap joint tests. Their behavior is completely different from brittle adhesive joints, and their modelling is more difficult with inaccurate results, which makes experimental tests crucial. With this study, future costs will be reduced when working with flexible adhesives since fractional factorial design 2 k allows to reduce drastically the number of tests. In this case, with three factors (adhesive thickness, substrates length, and width) and five specimens for each combination of them, tests were reduced from 300 to 40, with the subsequent cost reduction. The effect on shear stress, strain, Young’s modulus, and absorbed energy by the adhesive joint was studied, using steel substrates with polyurethane adhesive. It has been found that shear stress is mostly affected by the adhesive thickness, the higher the thickness, the lower the stress. In the case of strain, elastic modulus and absorbed energy, the most influent factor is the overlap length. It presents an inverse relation with strain and energy, and a direct one with modulus. With this method the effect of various factors can be known simultaneously.

A dynamic response analysis of adhesive - Bonded single lap joints used in military aircrafts made of glass fiber composite material undercyclic impact loading

The Colombian aeronautical industry has stimulated research into the mechanical behaviours of materials under the different loading conditions that aircrafts are generally exposed during their operation. Calima T-90, the first military aircraft that was built in Colombia, is used for the primary flights training of Colombian Air Force pilots, and is thus often exposed to adverse operating situations, such as hard landings, which cause impact loads and can subsequently produce impact fatigue. The Calima T-90's structure is mainly comprised of composites materials, generating assemblies and subassemblies of different components of it. The main method of bonding these components is by using adhesive joints with different thicknesses. This study aimed to characterise these adhesive joints as they were placed under typical loads. For this purpose, an evaluation of the effects of adhesive thickness on the mechanical performances of such joints was accomplished and conducted using quasi-static loading conditions and impact fatigue, employing single lap-joint (SLJ) specimens. Cyclic impacts were induced using a drop weight impact testing machine, in order to obtain the characteristic impact-fatigue life diagrams. The evolution of dynamic parameters was then analysed such as residual strength, impact contact time and stiffness degradation; this was done for all the adhesive thicknesses tested. A modified phenomenological prediction model for strength degradation and a cycle to failure prediction model in terms of the adhesive thickness of the joint, mass and the impact strain rate were proposed. It was found that the impact fatigue life of the joints decreased as adhesive thicknesses increased under the same linear momentum, however, this did not occur when the specimens were subjected to similar impact energy values. Subsequently, an analysis of the fracture surfaces of the specimens was conducted that, considered the mechanical interactions between the substrate and the adhesive, fiber tearing and debonding from the composite matrix was found as well as delamination, resulting in a beneficial adhesion mechanism.

The effect of bond-line thickness on fatigue crack growth rate in adhesively bonded joints

The effect of adhesive thickness on fatigue crack growth in an epoxy film adhesive (FM94) was investigated, using a combination of experiments and numerical modelling. For the range of thicknesses investigated an increased thickness led to an increased crack growth rate. It was found that the energy required per unit of crack growth did not depend on the adhesive thickness. In contrast, the energy available for crack growth does depend on the adhesive thickness.The numerical analysis confirms that the energy required per unit crack growth is not sensitive to the adhesive thickness, but that the plastic energy dissipation increases with the thickness. The experimental results imply that this increase of plasticity has an anti-shielding effect, as the crack growth rate is increased.

Experimental and Numerical Analysis of Epoxy Based Adhesive Failure on Mono- and Bi-Material Single Lap Joints Under Different Displacement Rates

Development in material science impose to use different materials in production. This causes a problem for joining different materials because traditional joining techniques such as welding could not overcome this problem in industries such as automotive. Hence, adhesive bonding overcomes this problem by its superiorities to join different materials. Joint strength of epoxy-based adhesives are affected by adhesive thickness, adherent’s surface quality and curing conditions. In this study, two different materials (SAE 304 and AL7075) were bonded by epoxy adhesive (3M DP460NS) as single lap joint (SLJ) of Aluminum-Aluminum, Steel-Steel and Aluminum-Steel. Effects of adhesive thickness (0.05, 0.13, 0.25 mm) and surface roughness (281, 193, 81 nm) to strength were compared. SLJs were tested for 1, 10, 25 and 50 mm/min displacement rates. Adhesive surface structures were imaged by Scanning Electron Microscopy (SEM) to investigate adhesive fractures. Surface roughness’s were examined by using Atomic Force Microscopy (AFM) to compare its influence on failure load. Finite Element Analysis (FEA) were conducted by using Cohesive Zone Model with ANSYS 18.0 software to obtain stress distribution of adhesive. Optimum values according to the present conditions of thickness(0.13mm) and roughness(<200nm) were determined. Experimental results were demonstrated that while displacement rates rose, failure loads increased as well. FEA analysis were fit to experimental results. It has been observed that along with material type, peel stresses become an important factor for joint strength.

Adhesive strength evaluation for three-dimensional butt joint in terms of the intensity of singular stress field on the interface outer edge

Our previous studies analyzed the adhesive strength of butt joint systematically in terms of the intensity of singular stress field (ISSF) by using two-dimensional modeling. In consideration of the actual specimen geometry, in this paper, the adhesive strength of butt joint is analyzed by using three-dimensional modeling. A mesh-independent numerical method combined with the finite element method (FEM) is used to calculate the ISSF. The ISSF distribution on the interface outer edge is analyzed, the effect of adhesive thickness is investigated. The ISSF at the interface vertex is analyzed by using a small fillet instead. The difference between 2D and 3D models for adhesive strength evaluation is discussed. The usability of 2D modeling is investigated.

Adhesive thickness effects on the mixed-mode fracture toughness of bonded joints

ABSTRACTAiming to predict the strength of bonded joints by techniques such as cohesive zone models (CZM), it is highly relevant to estimate the adhesive strength and fracture toughness (GC). Here, the tensile and shear fracture toughness (GIC and GIIC, respectively) and the corresponding mixed-mode behaviour acquire special relevancy. However, it is known that these parameters are highly dependent on the adhesive thickness (tA). The present work experimentally addresses the tA effect on the mixed-mode behaviour of bonded joints, namely on the tensile and shear fracture energies (GI and GII, respectively), using the Single-Leg Bending (SLB) test. Different data reduction schemes were applied. With this purpose, the respective resistance curves (R-curves) were calculated, which enabled plotting the respective fracture envelope for a sample tA by the knowledge of the pure-mode GIC and GIIC. Overall, it was possible to obtain a good agreement between methods for the mixed-mode GI and GII calculation and to estimate the most suitable fracture envelope of the adhesive for a given tA. The compliance-based beam method (CBBM) was found to be particularly suited to perform data reduction, since it accounts for the adhesives’ ductility and it is not affected by crack length (a) measuring errors.

Effect of adhesive thickness and overlap on the behavior of composite single-lap joints

The effect of adhesive thickness and adherent overlap on behavior of composite single-lap joints (SLJ) under tensile load is studied by using a 3D finite-element model. A bilinear Cohesive Zone Model (CZM) law is used to represent the adhesive behavior and its parameters are determined as a function of adhesive thickness by carrying out Double Cantilever Beam and End-Notched Flexure tests. The performance of SLJ is defined by peak load, maximum shear, and peel stresses. For the range of adhesive thicknesses considered, both maximum shear and peel stresses decrease with increasing adhesive thickness, while they increase with increasing overlap length.

Numerical study of the effect of carbon fiber/epoxy resin adhesive thickness on the creep behaviour of carbon steel plate joints

Nowadays, the use of adhesive and adhesively bonded joints have been considerably appreciated in the industry due to the dramatic reduction in bonding strength, reduced stress concentration, rust prevention, uniform bonding of the bonding surface and a significant reduction in costs compared to other types of permanent joints such as welding. In this study, the effect of adhesive thickness on creep behaviour of a single lap adhesive joint with the aid of Abaqus FEM software is investigated. It should be noted that the two-layer and two-dimensional models are considered, in which their adhesive layer is made of a reinforced epoxy resin with 0.5% carbon fiber and the adherend layers are made of carbon steel plates, which is affected by tensile forces. Since the main purpose of this paper is to study the effect of adhesive thickness on the adhesive joints behaviour, the effects of the distribution of shear stress, effective stress and creep strain were studied in different thicknesses of the adhesive layer. The results show that by increasing the thickness, the stress and the creep strain decrease, and over time, the stress decreases and the creep behaviour of adhesives increases.

Effect of adhesive thickness on the strength of steel-composite joints aged in wet environment

This paper presents the effect of adhesive layer thickness on the static strength of adhesively bonded steel-glass fiber-reinforced unsaturated polyester resin (GFRP) lap joints after being aged in water at a temperature of 60°C for 15 days. The adhesive thickness was varied from 0.1 mm to 0.5 mm. It was found that for the dry joints, the static strength increased with the increase of adhesive thickness. However, in wet condition, water really had a significant detrimental effect on the strength of the joints, as most of the strengths of wet joints were much lower than those of the dry joints. In dry condition, mode of failure changed from interfacial (at the adhesive thickness of 0.1 mm) to mix failure; however, for the wet joints; most of failures were at the interface of adhesive/steel.

On the effect of adhesive thickness on mode I fracture energy - an experimental and modelling study using a trapezoidal cohesive zone model

ABSTRACTIn this paper, a combined experimental-numerical method was proposed to study the effect of adhesive thickness on mode I fracture energy of the adhesive layer, using Double Cantilever Beam (DCB) testing and Cohesive Zone Modelling (CZM). A Trapezoidal Cohesive Zone Model (TCZM) was introduced in tabular form into commercial Finite Element (FE) package to simulate the crack propagation behaviour in the adhesive layer and include the ductile characteristics of the selected adhesive. In order to overcome the difficulty in the accurate monitoring and measurement of crack length during loading, the Compliance-Based Beam Method (CBBM) was adopted to deduce the mode I strain energy release rate data. The load–displacement curve, Resistance curve (R curve), and mode I fracture energy data obtained from both experiment and simulation were analysed to validate the established FE model. It was observed that adhesive thickness has a significant influence on the ductile fracture behaviour of adhesive under mode I loading. The mode I fracture energy increases initially, and then decreases with the increase of adhesive layer thickness in the selected thickness range, while obvious transition was also observed in the perspective of micro-scale failure mechanism of the fracture surface through Scanning Electron Microscopy (SEM).

Optical calcium test for measurement of multiple permeation pathways in flexible organic optoelectronic encapsulation.

Organic photovoltaic (OPV) devices and other organic electronics have the promise to provide lightweight, flexible alternatives to traditional rigid semiconductor technologies. However, organic electronics often degrade rapidly upon exposure to oxygen, water, light, and combinations thereof, as well as upon exposure to elevated temperatures. This requires the use of high gas barrier packaging in order for devices to have operational lifetimes on the order of years. To meet the challenge of transparent high gas barrier materials which maintain the flexibility of organic optoelectronics, many different materials and encapsulation schemes have been developed including the lamination of devices between flexible multi-layer barrier films. Because of their excellent barrier properties, these materials often require specialized testing for permeation measurements which evaluate materials independently. In this work, we demonstrate the use of an optical calcium test, which uses a sample geometry that closely mimics an OPV device, to evaluate a complete encapsulation scheme and to elucidate the relative importance of different permeation pathways. Using an encapsulation scheme of laminating a device between two multi-layer barrier films using an adhesive, measurements were made for water vapor permeation through the barrier film, the bulk adhesive, and along the adhesive-to-barrier film interface. The results show that the combined lateral permeation, including through the bulk adhesive and along the adhesive-to-barrier film interface, can constitute over 50% of the total permeation for small devices (4.5 cm × 4.5 cm). The adhesive-to-barrier film interface was also found to be a very important pathway as it was deemed responsible for more permeation than the bulk adhesive. The technique was also used to evaluate encapsulation design variables such as the effects of adhesive thickness and surface treatments on the lateral water permeation. We demonstrate that decreasing the adhesive thickness leads to a decrease in the lateral water permeation.

Effect of pre-installed corrosion on steel plate-CFRP bond characteristics

This paper presents an experimental study on the behavior and load carrying capacity of carbon fiber reinforced polymer (CFRP)-steel bonded joints with different levels of corrosion damage. The effects of adhesive thickness and corrosion damage in steel plates on CFRP-steel bond characteristics were evaluated using double-strap joint specimens. The experimental results indicated that the surface roughness associated with corrosion damage prior to an installation of the strengthening system initiated interlaminar failure in the CFRP plate. This effect was more pronounced in the specimens with high severity of corrosion damage and thick adhesive layer. The ultimate load of the specimens with corroded steel plates was higher than that of the specimens without damage due to mechanical interlocking. The applicability of available theoretical models on the effective bond length and load capacity calculations was evaluated for the strengthened system with corrosion damage.

Experimental and Simulation Study on the Effect of Adhesive Thickness on Mode I Fracture Toughness

Experimental and Simulation Study on the Effect of Adhesive Thickness on Mode I Fracture Toughness

Effects of adhesive thickness on the Lamb wave pitch-catch signal using bonded piezoelectric wafer transducers

This paper investigates the effects of adhesive layer on Lamb wave ultrasound pitch-catch signals that are excited and sensed by piezoelectric wafer transducers bonded on a slender structure. Analytical models were established to simulate the longitudinal and flexural vibrations of the structures separately and parametric studies of the bonding layer properties, i.e. the shear transfer parameter, adhesive thickness, and shear modulus, were performed. The parametric studies indicate that there exists an optimal adhesive layer thickness that generates maximum ultrasound pitch-catch signal for both wave modes. This prediction was subsequently validated by measurements. In addition, an improved match between the measured and simulated pitch-catch signals was achieved by adjusting the adhesive layer parameters.

Theoretical model of adhesively bonded single lap joints with functionally graded adherends

Adhesively bonded joints with functionally graded (FG) adherends are of practical significance since tailoring material composition through the adherend thickness can lead to more uniform shear or peeling stress distributions in the adherends and the adhesive layer near the edges of the joint. Stresses at the free edges of the adhesive layer have been found to be critical to the integrity of the joint. To this end, an analytical model is proposed for an adhesively bonded single lap joint with FG adherends. In this model, the adhesive layer is modeled as a three parameter, elastic foundation, allowing for different peel stress values at the two adherend-adhesive interfaces. Closed-form expressions for interface stresses and internal forces in the adherends are obtained. The model is validated by its agreement with finite element analysis simulations. This model shows that the peel stresses are critical at the left edge of the upper adherend-adhesive interface and at the right edge of the lower adherend–adhesive interface, suggesting that the joint is vulnerable to delaminations along the upper adherend-adhesive interface at the left edge and along the lower adherend-adhesive interface at the right edge. Parametric studies reveal the effects of adhesive thickness, adhesive stiffness, and FGM configuration on the stresses within the single lap joint. Results show that stress concentrations can be reduced near the edges of the joint by increasing the thickness of the adhesive layer, reducing the Young’s modulus of the adhesive layer, and/or configuring the FG adherends so that the stiffer material is nearest the adhesive layer.

Effect of adhesive thickness on the Mode I and II strain energy release rates. Comparative study between different approaches for the calculation of Mode I &amp; II SERR's

Abstract The assembly of composite components using adhesives, is one of the principal methods used for the assembly process. Composite materials have lately been used extensively in different engineering domains, as a result their use in wind energy, or specifically wind turbine blades has also seen a significant increase. This paper deals with the problem of determining the resistance of bonding and the effect of adhesive thickness on the resistance based on the strain energy release rate in both Mode I (peeling) and Mode II (shearing) type failure. Different theories are used to measure the SERR's and the effect of thickness on the measured SERR can be seen pronounced with each theory. This has been attributed to the type of failure and also the deformation of the interface before failure in each thickness case.

Effect of adhesive thickness and surface roughness on the shear strength of aluminium one-component polyurethane adhesive single-lap joints for automotive applications

Adhesively bonded technology is now widely accepted as a valuable tool in mechanical design, allowing the production of connections with a very good strength‐to‐weight ratio. The bonding may be made between metal–metal, metal–composite or composite–composite. In the automotive industry, elastomeric adhesives such as polyurethanes are used in structural applications such as windshield bonding because they present important advantages in terms of damping, impact, fatigue and safety, which are critical factors. For efficient designs of adhesively bonded structures, the knowledge of the relationship between substrates and the adhesive layer is essential. The aim of this work, via an experimental study, is to carry out and quantify the various variables affecting the strength of single-lap joints (SLJs), especially the effect of the surface preparation and adhesive thickness. Aluminium SLJs were fabricated and tested to assess the adhesive performance in a joint. The effect of the bondline thickness on the lap-shear strength of the adhesives was studied. A decrease in surface roughness was found to increase the shear strength of the SLJs. Experimental results showed that rougher surfaces have less wettability which is coherent with shear strength tests. However, increasing the adhesive thickness decreased the shear strength of SLJs. Indeed, a numerical model was developed to search the impact of increasing adhesive thickness on the interface of the adherend.

Effect of adhesive thickness on the wettability and deformability of polyacrylic pressure‐sensitive adhesives during probe tack test

ABSTRACTEffect of adhesive thickness on the wetting and deformation behaviors during probe tack test of pressure‐sensitive adhesive (PSA) was investigated. For this purpose, cross‐linked poly(n‐butyl acrylate‐acrylic acid) [P(BA‐AA)] and poly(2‐ethylhexyl acrylate‐acrylic acid) [P(2EHA‐AA)] random copolymers with an acrylic acid content of 5 wt % and thicknesses in the range of ∼15–60 μm were used. Tack was measured using the probe tack test and the fracture energy was calculated from the areas under force–displacement curve recorded during debonding process. From contact time dependence of fracture energy, the rising rate of fracture energy with contact time increased with increasing of adhesive thickness and was P(2EHA‐AA) &gt; P(BA‐AA). The fracture energy was P(BA‐AA) &gt; P(2EHA‐AA) at shorter contact time, whereas it reversed at longer contact time. This was caused by two different interfacial adhesions: the physical wetting of PSA molecules to the adherend surface with contact time and the chemical interaction between the acrylic acid units and the adherend surface. From the force–displacement curve measured under the condition of sufficient interfacial adhesion, both maximum force and displacement—namely, the deformability of PSA during debonding process—increased with adhesive thickness. The degree of increase of deformability was P(2EHA‐AA) &gt; P(BA‐AA). The fracture energy was found to depend on the development of interfacial adhesion during contacting process and the deformability of PSA during debonding process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43639.