Effect Of Bond Thickness Research Articles

Bond thickness effect in mixed-mode fracture and its significance to delamination resistance

The fracture behavior of adhesively bonded joints is of interest in a variety of industrial, natural and biological applications. This effort re-examines literature data with an emphasis on thin bonds and their relation to delamination resistance. Brittle, ductile and particulate epoxy adhesives were considered with the bond thickness t varying from 1 to 1000 μm. The results shed new light on some basic morphological and fracture characteristics. The fracture energy is affected by numerous factors including adhesive material, bond thickness and loading mode. Shear fracture generally begins with growth of tensile microcracks ahead of the crack tip and continues with coalescence of these cracks along the interface in a process accompanied by extensive plasticity. With GIIC ≈ GIIIC, mixed-mode fracture can be described by tensile (GI) vs. shearing (GSC) ERR. For thin bonds (t < ≈ 10 μm), GIC ≈ constant, GSC increases virtually linearly with t, and GSC ≈ GIC = G0 when t → 0. These traits result in a closed-form expression for GC given in terms of basic material properties. The thin-bond results provide cost-effective means for predicting interlaminar fracture energy GIC or GIIC and elucidating an interleaf thickness for optimal delamination resistance. A detailed examination of published data reveals that within certain limitations, the mixed-mode fracture envelope is independent of t or material type. This finding may help develop analytical fracture models for practical use.

Carbon nanotube embedded adhesives for real-time monitoring of adhesion failure in high performance adhesively bonded joints

Carbon nanotubes (CNTs) embedded polymers are of increasing interest to scientific and industrial communities for multi-functional applications. In this article, CNTs have been introduced to high-strength epoxy adhesive for enabling in-situ strain sensing in adhesively bonded aluminium-to-aluminium single-lap joints to accurately indicate the onset and propagation of adhesion failure to the evolution of piezo-resistivity in varying mechanical loads. The CNT modified adhesive in bonded joints and the CNT modified adhesive alone have been tested under monothonic and cyclic tensile loads up to ultimate failure. The changes in the piezo-resistivity induced by the CNTs have been monitored in situ with respect to loading. A novel interpretation method has been developed for progressive, instantaneous adhesion failure estimation under cyclic tensile stresses from a resistivity baseline. The method indicates that the in-situ resistivity changes and the rate of the changes with strain, i.e. sensitivity, strongly correlate with the adhesion failure progression, irrespective of the CNT dispersion quality. Moreover, the effect of bond thickness on the evolution of piezo-resistivity and adhesion failure have been studied. It was observed that relatively thin adhesive bonds (0.18 mm thickness), possessing higher CNT contact points than thick bonds (0.43 mm thickness), provide 100 times higher sensitivity to varying cyclic loads.

Experimental Investigation on the Effect of Bond Thickness on the Interface Behaviour of Fibre Reinforced Polymer Sheet Bonded to Timber

Experimental Investigation on the Effect of Bond Thickness on the Interface Behaviour of Fibre Reinforced Polymer Sheet Bonded to Timber

Micro-mechanical behaviour of artificially cemented sands under compression and shear

The mechanical behaviour of cemented sands at macro-scale has been widely studied in the past, while there is still a lack of laboratory test data for the micro-mechanical response. Therefore, a series of uniaxial compression and tangential shear tests on artificially cemented sand particles have been conducted using a microscope to observe their behaviour. First, the consistency of cemented particles with different cementing agents is discussed. Three breakage modes are proposed according to the images taken using a microscope camera. A new parameter named ‘local roundness at contact’ is introduced to emphasise the effect of contact morphology on sample strength. Moreover, the effect of bond thickness on the mechanical response of cemented particles has been investigated. Finally, the shear strength parameters of artificially cemented sand samples have been determined for two different sample diameters.

Fracture Characteristics of Shear Adhesive Dissimilar Joint

In this study, the effect of bond thickness upon shear strength and fracture toughness of epoxy adhesively bonded joint with dissimilar adherents was addressed. The bond thickness, t between the adherents was controlled to be ranged between 0.1 mm and 1.2 mm. Finite element analyses were also executed by commercial ANSYS 11 code to investigate the stress distributions within the adhesive layer of adhesive joint. As a result, shear strength of adhesive joint reduces with increasing bond thickness. The strength of shear adhesive joint was also depended on elastic modulus of adherent. Moreover, the failure of dissimilar adherents bonded shear joint originated at a location with critical stress-y which was the interface corner of ALYH75/epoxy. In the case of shear adhesive joint with an interface crack, the fracture also occurred at the ALYH75/epoxy interface even in the steel-adhesive-aluminum (SEA) specimens. Fracture toughness, Jc of aluminum-adhesive-steel (AES) joints was similar to those of SES and demonstrates strong dependency upon bond thickness. Furthermore, the interface crack in SEA specimen has relatively large fracture resistance if compared to those in AES specimen. Finally, Kc fracture criterion was found to be appropriate for shear adhesive joints associated with adhesive fracture.

3D Finite Element Stress Analysis of Butt Adhesively Bonded Dissimilar Joint: Effect of Bond Thickness on Strength

The butt joint is the most studied type of adhesive joints in the literature. However, the joint strength prediction of joints is still a controversial issue as it involves a lot of factors that are difficult to quantify such as the yielding of the adherend, the plasticity of the adhesive and the bondline thickness. The present work is concerned with the three dimensional (3D) finite element stress analysis of butt adhesively bonded dissimilar joint. The objective of the present study was to analyse the effect of bond thickness on mechanical strength of butt adhesively bonded dissimilar joint. Aluminum alloy and steel were selected and five thicknesses were studied for each adherend: 0.2, 0.4, 0.6, 0.8, and 1.0 mm respectively. In order to quantify the influence of bondline thickness, adherend and durability of the butt joint, the 3D finite element models of ANSYS used to obtain the stress distributions. Mechanical properties of adhesive were determined by tensile test and ANSYS analysis. A statistical analysis of simulation results shows that the butt joint strength becomes stronger while the bondline gets thinner and adhesive gets tougher.

A bond failure criterion for DEM simulations of cemented geomaterials considering variable bond thickness

SUMMARYA series of micromechanical tests were conducted to investigate the bond failure criterion of bonded granules considering the effect of bond thickness, with the aim of enhancing the bond contact model used in the distinct element simulations of cemented geomaterials. The granules were idealized in a two‐dimensional context as one pair of aluminum rods bonded by resin epoxy or cement. The mechanical responses of nearly 500 rod pairs were tested under different loading paths to attain the yield loads of bonded granules at variable bond thickness. This study leads to a generic bond failure criterion incorporating the effect of the bond thickness. The results show that the bond compressive resistance largely decreases with increasing bond thickness owing to the presence of the confinement at the bond‐particle interface. The strength envelopes obtained from the combined shear compression tests and combined torsion compression tests have identical functional form, and they decrease in size with increasing bond thickness but remain unchanged in shape. Given the same cementation material, the generic bond strength envelope in a three‐dimensional contact force space under different loading paths remains the same in shape but shrinks with the increase of bond thickness. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Strength prediction and reliability of brittle epoxy adhesively bonded dissimilar joint

This paper deals with strength and failure prediction as well as reliability issues of adhesive joints of brittle epoxy bonding of two dissimilar adherends. Effects of bond thickness and scarf angle upon the strength of such joints are also addressed. Three kinds of adhesive joints, i.e., butt, scarf and shear joints, are considered. It is found that the strength prediction of various adhesive joints under consideration can be done by establishing interface corner toughness, Hc, parameter. For adhesive joints with an interfacial crack, fracture toughness, Jc, or interfacial toughness, Kc, can be used as a fracture criterion depending on the fracture type observed. The predicted strengths based on these fracture criteria (i.e., Hc, Jc and Kc) are in good agreement with experimental data obtained. Weibull modulus is a suitable parameter to define the strength reliability of adhesive joints. From experimental data, scarf joint of 45° is identified to be preferable since it satisfies both outstanding load-bearing performance and tolerable reliability. In addition, the Weibull statistical method has made possible the strength reliability determination of non-cracked adhesive joints.

Prediction of Strength and Failure for Brittle Epoxy Adhesive Joints of Dissimilar Adherends

This paper deals with the strength and failure prediction as well as the reliability issues of adhesive joints of brittle epoxy bonding two dissimilar adherends. The effects of bond thickness and scarf angle upon the strength of such joints are also addressed. Three kinds of adhesive joints, i.e., butt, scarf and shear joints are considered. It is found that the strength prediction of various adhesive joints can be done by establishing the interface corner toughness, Hc parameter. Weibull modulus is suitable to define the reliability of adhesive joints. The scarf joint of 45° is identified to be preferable since it satisfies both outstanding load-bearing performance and tolerable reliability. Hence, both applications of Hc parameter and Weibull statistical method allow the strength and failure predictions of adhesive joints with fairly improved reliability.

Fracture Toughness Test of Epoxy Adhesive Dissimilar Joint with Various Adhesive Thicknesses

In this study, effect of bond thickness upon the strength and fracture toughness of epoxy adhesive dissimilar joint is investigated. Tensile and three-point-bending (abbreviated as 3PB hereafter) fracture tests are conducted. Finite element method (abbreviated as FEM hereafter) analysis is also executed to analyze the stress distribution at an interface corner of dissimilar joint. From FEM analysis results, it is found that the stress singularity in the dissimilar joint exists pronouncedly at the SUS304/adhesive interface corner and the order of stress singularity in the tensile model is higher than that in the 3PB model. Moreover, the order of stress singularity in the dissimilar joint having bond thickness of 1.0 mm is quite identical to the value obtained from analytical solution under the plane stress condition. From 3PB test and tensile test, it has been confirmed that the failure stress of dissimilar joint slightly increases with the decreasing bond thickness and can be well predicted by using the interface corner toughness, Hc parameter. The failure of dissimilar joints always originates from the SUS304/adhesive interface corner and the failure stress for dissimilar joint of 3PB test is higher than that of tensile test. For the specimens failed at the ALU/adhesive interface corner, the poor wettability of ALU adherend’s surface plays an important role. For the dissimilar joint with an interfacial crack, the fracture toughness, Jc is calculated by J integral method in FEM analysis. Fracture toughness, Jc for cohesively fractured specimens is more or less constant but shows some dependency on bond thickness for interfacially fractured specimens. Locus of fracture can be best interpreted in terms of stress singularity order at the interfacial crack tip.

609 エポキシ系異材継手のせん断強度及び破断特性の評価(OS10-(1)オーガナイズドセッション《材料損傷の機構・実験評価》)

In this paper, the effect of bond thickness upon the shear strength of epoxy adhesively bonded joints with dissimilar adherends is addressed. The bond thickness, t between the adherends is controlled to be ranged from 0.1 mm to 1.2 mm. Finite element analyses are also executed by ANSYS 11 code to investigate the stress distributions in adhesive layer of adhesive joints. The order of stress singularity is obtained from the analytical solution of Bogy's characteristics equation. As a result, shear strength of adhesive joint reduces with increasing bond thickness. Moreover, the failure of dissimilar adherends bonded shear joint has been initiated at a location with critical stress singularity order which is the interface corner of aluminium/adhesive. It is found that the shear strength prediction can be satisfactorily done by interface corner toughness, Hc parameter.

Effect of Bond Thickness on Fracture Behavior of Interfacial Crack in Adhesive Joint of Dissimilar Materials

本研究では，モードI負荷の下でSUS304とアルミ合金からなるエポキシ系異材継手の界面き裂の破壊特性について様々な接着層厚さの影響を調べた。そして，汎用解析コードANSYS11を用いて接着層内の応力分布や異材継手の破壊じん性を評価した。破壊試験の結果から，き裂のない異材継手の強度は接着層が厚くなるとともに減少する傾向が見られた。この場合，小規模降伏条件が満たされるならば接着継手の強度の推測は界面コーナーじん性，Hcが使用できることが分かった。また，界面き裂の進展方向は2種類に分類できる，即ち，界面に沿って進む(i.e.界面破壊）あるいは接着層内に屈折する(i.e.凝集破壊)。次に，求めた界面き裂付き異材継手の破壊じん性Jcは，き裂が接着層内に屈折した場合，接着層厚さによらずほぼ一定である。他方，界面破壊の場合，Jcは接着層厚さに依存性がある。そこで，界面き裂は二つの剛体に挟まれた接着層の中央き裂と近似すると，界面破壊した異材継手の破壊じん性はKｃのパラメータで評価できることが分かった。

Fracture Mechanics Characterization of Composite/Metal Interfaces of Bonded Joints

Adhesive bonding between different materials has been widely used for a large variety of applications, such as in the aircraft, automotive, and many other civil engineering structures. Adhesive-bonded joints as load bearing components have the potential to save significant weight and cost over conventional riveted or bolted joints. For the last ten years a major problem in adhesive technology has been the difficulty in predicting the accurate load bearing capacity of a joint. This difficulty comes from the fact that the stress distribution in the adhesive joint is very complex and singular stress field exists at the bi-material corner. And for bonded joints, the failure usually occurs at the adhesive/adherend interface. Therefore another difficulty comes from the complex interfacial failure analysis due to the formation of chemical bonds, whose strengths are difficult to measure. Many studies have been conducted to investigate the effects of bond thickness, material properties of adhesives and adherends, and geometric shape of bi-material corner tip to the fracture behavior of bonded joints. In this paper, we analyze the stress fields at the interface corner of composite/steel(anisotropic/isotropic) double lap joint to predict failure by using stress intensity based fracture criterion. And analytical results are compared with experimental results of co-cured lap joints under tensile load condition. Micro-structural features, hardness characteristics, and fracture toughness determinations of the interfaces are also conducted.

Bond thickness effect on impact response and damage of adhesively-bonded graphite/epoxy composites

Adhesively-bonded composites are often subjected to impact during manufacturing or service. This impact may result in a reduction in strength and structural integrity of engineering components made of adhesively-bonded composite structures. In this study, an impact test was carried out on adhesively-bonded graphite/epoxy composite panels at different low impact energies, ranging from 5 to 20 J, using a drop-weight impact test equipment. The effect of bond thickness on impact response and the resulting damage was investigated. The resulting internal damage due to impact on the adhesive bondline was interrogated using ultrasonic nondestructive evaluation. The ultrasonic C-scan of the gated ultrasonic wave signal was acquired and the ensuing debond area was determined quantitatively for specimens joined by different thickness adhesive bonds. The results revealed that increasing the thickness of the bond increased the maximum contact force reached during impact. In addition, the shape and size of the debond area in the adhesive layer showed dependence on both bond thickness and impact energy.

接着継手の破壊靭性値に与える接着剤層厚さの影響とそのメカニズムについて

接着継手の破壊靭性値に与える接着剤層厚さの影響とそのメカニズムについて

Effect of bond thickness on creep lifetime of adhesive joints under mode I

An experimental investigation has been carried out on double cantilever beam specimens with different bond thicknesses to study the effect of bond thickness on lifetime of adhesive joints under mode I. This paper describes an approach to predict the rate of crack propagation. The approach is based on principles of linear elastic fracture mechanics and uses elevated temperature to accelerate the crack propagation under constant loads. The fracture energy of the joint is studied as a function of bond thickness. The results from short-term tests are analyzed and a simple model has been proposed to predict the variation of two kinetic parameters of the Paris law with bond thickness.

The effects of bond thickness, rate and temperature on the deformation and fracture of structural adhesives under shear loading

The deformation and fracture in shear of a structural adhesive undergoing large-scale yielding is studied as a function of bond thickness, h, temperature, T , and strain rate using the Napkin Ring specimen. The lack of edges in this test, and the fact that the strain rate can be locally controlled, allow for a meaningful evaluation of the mechanical response throughout the deformation process. In accord with Airing's molecular activation model, the yield stress linearly decreases with T while logarithmically increasing with the strain rate. The ultimate shear strain, γF, is little sensitive to rate while decreasing with h and increasing with T. Some complementary fracture tests are carried out using the ENF bond specimen in order to explore the relation between the mechanical properties of the nominally unflawed adhesive and the mode II fracture energy, GIIC. For sufficiently thin bonds, GIIC/h correlates well with the ultimate energy density (i.e., the area under the stress-strain curve in the Napkin Ring test), given, to a first approximation, by τYγF ,w hereτY is the yield stress in shear. Accordingly, the fracture energy of the bond would be greatly affected by temperature, tending to a small value at the absolute as well as the glass transition temperatures while attaining a maximum in between these two extremes. Because the yield stress does not vary much with h, the variation of GIIC with the bond thickness reflects that of γF. A large-deformation fracture analysis, based on a cohesive zone like model, is developed to account for the observed variations of γF with h. The analysis assumes that a crack preexist in the bond, either at its center or at the interface. The results suggest that the observed increase of γF with decreasing h is due mainly to two geometric effects. The first is due to the interaction of the bonding surfaces with the stress field generated by the crack and the second has to do with the probability of finding large flaws in the bond to trigger the fracture.

Effect of Bond Thickness on the Fracture Toughness of Adhesive Joints

The effect of bond thickness on the fracture toughness of adhesive joints was investigated from a microstructural perspective, using compact tension (CT) adhesive-joint specimens with different bond thicknesses. The adhesive material was a rubber-modified epoxy resin with 12.5 wt% carboxy-terminated butadiene acrylonitrile (CTBN) elastomer. The shapes of the rubber particles dispersed in adhesive layers of damaged and undamaged specimens were observed with an optical microscope. The damage was distributed along the interfaces between the adhesive layer and the two adherends. The results show that the primary causes of variations in the fracture toughness of an adhesive joint with the bond thickness are not only a damage zone around a crack tip but also the combination of a damage zone around a crack tip and additional damage zones along the interfaces.

121 接着継ぎ手の破壊靱性値に対する接着剤層厚さ効果のメカニズム

121 接着継ぎ手の破壊靱性値に対する接着剤層厚さ効果のメカニズム

Effect of Bond Thickness on Fracture Behaviour in Adhesive Joints

To study the effects of bond thickness on the fracture behaviour of adhesive joints, experimental investigation and finite element analysis have been carried out for compact tension (CT) and double-cantilever-beam (DCB) specimens with different bond thickness. Fractography and fracture toughness exhibited apparent variations with bond thickness. Numerical results indicate that the crack tip stress fields are affected by bond thickness due to the restriction of plastic deformation by the adherends. At the same J level, a higher opening stress was observed in the joint with a smaller bond thickness (h). Beyond the crack tip region, a self-similar stress field can be described by the normalized loading parameter, J/hσ0. The relationship between J and crack tip opening displacement, δ, is dependent on the bond thickness. The strong dependence of toughness upon bond thickness is a result of the competition between two different fracture mechanisms. For small bond thickness, toughness is linearly proportional to bond thickness due to the high constraint. After reaching a critical bond thickness, the toughness decreases with further increase of bond thickness due to the rapid opening (blunting) of the crack tip with loading. A simple model has been proposed to predict the variation of toughness with bond thickness.