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Herzl Chai - One of the best experts on this subject based on the ideXlab platform.
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Bond Thickness effect in mixed mode fracture and its significance to delamination resistance
International Journal of Solids and Structures, 2021Co-Authors: Herzl ChaiAbstract:Abstract 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
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the effects of Bond Thickness rate and temperature on the deformation and fracture of structural adhesives under shear loading
International Journal of Fracture, 2004Co-Authors: Herzl ChaiAbstract: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.
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interfacial mixed mode fracture of adhesive Bonds undergoing large deformation
International Journal of Solids and Structures, 2003Co-Authors: Herzl ChaiAbstract:Interfacial fracture of adhesive Bonds undergoing large-scale yielding is studied using a combined experimental/ finite-element approach. The full range of in-plane mode mixity is produced over Bond Thickness ranging from 30 to 500 lm using the scarf and the ENF joint geometries. Novel techniques for introducing pre-cracks and surface decoration, together with in situ observations, facilitate accurate determination of the Bond-average and the local shear strains at the crack tip during the onset as well as the rest of the crack propagation event. The crack generally grew along one of the two interfaces of the Bond, although the failure was always fully cohesive. The local shear strain at the crack tip is independent of the Bond Thickness, and, under quasi-static conditions, it remains constant throughout the growth, which make it a viable fracture parameter. This quantity strongly depends on the mode mixity, the sign of the phase angle (i.e., shearing direction) and the crack speed, however. A finite-element analysis is used to obtain the crack tip deformation field for an interface crack in adhesively Bonded scarf and ENF joints. Large-strain and quasi-static conditions are assumed. A distinct material model in the fracture process zone that allows for volume change in the post-yield regime is incorporated into the analysis. The local deformation is characterized by a pair of Bond-normal and tangential displacements corresponding to the nodal points adjacent to the crack tip. The critical values of these quantities are obtained when the FEM Bond-average shear strain at the crack tip becomes equal to its experimental counterpart. The so defined critical local displacements, after an appropriate normalization, seem to conform to a single-valued, linear type interrelationship over the entire range of mode mixity. The fact that this relationship is independent of the Bond Thickness, and furthermore it encompasses both cases of positive and negative phase angles, makes it a viable candidate for characterizing mixed-mode interfacial fracture under large-deformation conditions. 2003 Elsevier Ltd. All rights reserved.
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observation of deformation and damage at the tip of cracks in adhesive Bonds loaded in shear and assessment of a criterion for fracture
International Journal of Fracture, 1993Co-Authors: Herzl ChaiAbstract:The evolution of damage at the tip of cracks in adhesive Bonds deforming in shear was monitored in real time using a high-magnification video camera. Brittle and a ductile epoxy resins were evaluated, with the Bond Thickness t being an experimental variable. An extensive zone of plastic deformation developed ahead of the crack tip prior to fracture. In the case of the brittle adhesive, for relatively thick Bonds tensile microcracks formed within that zone. Increased loading caused the microcracks to grow from the interlayer to the interface, which led to a complete Bond separation after interface cracks emanating from adjacent microcracks linked. In contrast, for the ductile adhesive the crack always grew from the tip. Strain gradients tended to develop there when the Bond Thickness was large.
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Bond Thickness Effect in Adhesive Joints and Its Significance for Mode I Interlaminar Fracture of Composites
Composite Materials: Testing and Design (Seventh Conference), 2026Co-Authors: Herzl ChaiAbstract:The effect of constraining the crack-tip damage zone on the Mode I fracture of a toughened epoxy resin (BP-907) was studied systematically using the double-cantilever-beam (DCB) adhesive joint specimen and scanning electron microscopy (SEM). While a broad Bond Thickness range was employed (5 33 μm the fracture energy exhibited dramatic variations with t that were shown to follow from the variations in size of a certain dimple-like morphological feature. In constrast, the arrest energy was fixed, in consistency with the unchanging morphology. The fracture behavior for t < 33 μm was equally interesting, now though because Gic was fixed while G 1 C a varied with t. These changes in failure conditions were accompanied by morphological changes; as t decreased from 33 μm, the failure locus shifted from the Bond center to the metal/matrix interface, and the failure itself occurred by shear yielding. Similarities were found in the failure conditions of butt joint and DCB adhesive specimens, on the one hand, and in that of the latter and composite interlaminar fracture, on the other hand, which suggest an interrelationship among these three failure phenomena.
E.d. Reedy - One of the best experts on this subject based on the ideXlab platform.
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connection between interface corner and interfacial fracture analyses of an adhesively Bonded butt joint
International Journal of Solids and Structures, 2000Co-Authors: E.d. ReedyAbstract:Abstract Interfacial crack growth in a tensile-loaded, adhesively-Bonded butt joint with rigid adherends is analyzed. First, the asymptotic, small-scale cracking solution for a short interfacial crack originating at a sharp interface corner is presented. Then the asymptotic, steady-state solution for a long interfacial crack is discussed. These asymptotic results are compared with full finite element solutions of a butt joint containing a 0.001 to 10 Bond Thickness long interfacial crack. Finally, the applicability of both interface corner and interfacial fracture mechanics approaches to failure analysis is discussed. The small-scale cracking solution indicates that when one can apply an interface corner failure analysis, one can also apply an interfacial fracture mechanics approach with a suitably chosen inherent flaw. Although the two methods are equivalent, it should be emphasized that the inherent flaw and corresponding toughness may have limited physical significance.
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Interface Corner Failure Analysis of Joint Strength: Effect of Adherend Stiffness
International Journal of Fracture, 1997Co-Authors: E.d. Reedy, T.r. GuessAbstract:The strength of cylindrical butt joints, fabricated by Bonding either aluminum or steel adherends together with an epoxy adhesive, has been determined for a wide range of Bond Thicknesses. Joint strength varied significantly with Bond Thickness. The measured strength of joints with steel adherends varied as the inverse cube root of Bond Thickness, while the strength of joints with aluminum adherends varied as the inverse fourth root of Bond Thickness. This Bond Thickness dependence is accurately predicted by an analysis that assumes failure occurs at a critical value of the interface corner stress intensity factor. The difference in the measured joint strength-Bond Thickness relation for joints with aluminum and steel adherends is a consequence of the difference in the order of the interface corner stress singularity.
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comparison of butt tensile strength data with interface corner stress intensity factor prediction
International Journal of Solids and Structures, 1993Co-Authors: E.d. Reedy, T.r. GuessAbstract:Abstract The butt tensile strength of a joint that Bonds two stainless steel rods together with an unfilled epoxy adhesive (Epon 828/T-403) has been determined for a wide range of Bond Thicknesses. The measured joint strength shows a pronounced Bond Thickness dependence; joint strength increases by a factor of 2 as Bond Thickness is reduced from 2.0 to 0.25 mm. A failure criterion, based upon a critical interface corner stress intensity factor, accurately predicts the observed Bond Thickness effect. This fracture criterion suggests that the strength of an adhesively Bonded butt tensile joint of one Bond Thickness can be estimated from strength data for a joint with a different Bond Thickness by the simple relation σ ult t 2 = σ ult t 1 ( h 1 / h 2 ) 1/3 , where 2 h i is Bond Thickness, σ ult ti is the nominal butt tensile strength, and subscript i = 1, 2 identifies the two joints with differing Bond Thickness. This relation applies to thin Bonds when the adhesive's Poisson's ratio is between 0.3 and 0.4, the adherends are relatively stiff, and small scale yielding conditions hold at the interface corner.
Hamed Yazdani Nezhad - One of the best experts on this subject based on the ideXlab platform.
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Carbon nanotube embedded adhesives for real-time monitoring of adhesion failure in high performance adhesively Bonded joints
Scientific Reports, 2020Co-Authors: Tadej Bregar, Somayeh Gharavian, Marek Burda, Isidro Durazo-cardenas, Vijay Kumar Thakur, David Ayre, Marcin Słoma, Mark Hardiman, Conor Mccarthy, Hamed Yazdani NezhadAbstract: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.
Tokuo Teramoto - One of the best experts on this subject based on the ideXlab platform.
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Author's personal copy Strength prediction and reliability of brittle epoxy adhesively Bonded dissimilar joint
2020Co-Authors: Mohd Afendi, R Daud, M Abdul S Majid, Abdul A Rahman, Tokuo TeramotoAbstract:This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. a b s t r a c t 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, H c , parameter. For adhesive joints with an interfacial crack, fracture toughness, J c , or interfacial toughness, K c , can be used as a fracture criterion depending on the fracture type observed. The predicted strengths based on these fracture criteria (i.e., H c , J c and K c ) 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 451 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 noncracked adhesive joints
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strength prediction and reliability of brittle epoxy adhesively Bonded dissimilar joint
International Journal of Adhesion and Adhesives, 2013Co-Authors: Mohd Afendi, Majid Abdul, R Daud, Rahman A Abdul, Tokuo TeramotoAbstract: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 451 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 noncracked adhesive joints.
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strength and fracture characteristics of sus304 al alloy scarf adhesive joint with various adhesive Thicknesses
Key Engineering Materials, 2011Co-Authors: Mohd Afendi, Tokuo Teramoto, Akihiro MatsudaAbstract:In this study, strength and fracture toughness of epoxy adhesively Bonded scarf joints of dissimilar adherends, namely SUS304 stainless steel and YH75 aluminium alloy are examined on several scarf angles and various Bond Thicknesses under uniaxial tensile loading. Scarf angles, θ = 45°, 60° and 75° are employed. The Bond Thickness, t between dissimilar metals is controlled to be ranged between 0.1 mm to 1.2 mm. Finite element (FE) analysis is also executed to investigate the stress distributions in the scarf joints by ANSYS 11 code. From analytical solutions, stress singularity exists most pronouncedly at the steel/adhesive interface corner of joints having 45° to 75° scarf angle. This is not only in agreement with the FE analyses results but also confirmed by fracture surfaces observation wherein the fracture has always been initiated at this point. The strength of scarf joints increases as the Bond Thickness decreases. Interface corner toughness, Hc approach can be applied when predicting the failure stress of scarf joints. Besides, for scarf joints with an interfacial crack, the fracture toughness, Jc values are independent of Bond Thickness and less sensitive to adherends. Moreover, Jc increases as mode mixity increases.
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fracture toughness test of epoxy adhesive dissimilar joint with various adhesive Thicknesses
Journal of Solid Mechanics and Materials Engineering, 2010Co-Authors: Mohd Afendi, Tokuo TeramotoAbstract: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.
Yiuwing Mai - One of the best experts on this subject based on the ideXlab platform.
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effect of Bond Thickness on fracture behaviour in adhesive joints
Journal of Adhesion, 2001Co-Authors: Cheng Yan, Yiuwing MaiAbstract:Abstract 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 propo...
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effects of constraint on crack tip stress fields and fracture toughness in adhesive joints
European Structural Integrity Society, 2000Co-Authors: Cheng Yan, Yiuwing MaiAbstract:Experimental investigation and finite element analysis have been carried out to study the fracture behaviour of adhesive joints under mode-I loading. Fractography and fracture toughness showed apparent variation with Bond Thickness. Numerical results indicated that at the same loading level, a higher opening stress was obtained in the joint with a smaller Bond Thickness (h) under both elastic and elastic-plastic conditions. The region dominated by crack singularity is much smaller than the Bond Thickness. Small-scale yielding conditions for homogeneous material cannot be directly applied to adhesive joints. Beyond the crack tip region, a self-similar stress field can be described by the normalised loading parameter J/hδo. The relationship between J and crack tip opening displacement is dependent on the Bond Thickness. The strong dependence of toughness upon Bond Thickness is likely to be a result of the competition between two different fracture mechanisms. A simple model has been proposed to predict the variation of toughness with Bond Thickness
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mode l fracture behaviour of adhesive joints part i relationship between fracture energy and Bond Thickness
Journal of Adhesion, 1995Co-Authors: Hamid Reza Daghyani, Yiuwing MaiAbstract:Abstract The fracture properties of adhesive joints of aluminium were investigated using a rubber-modified tough epoxy resin system (GIC = 2.76 kJ/m2) as adhesive material. Compact tension (CT) adhesive joints were manufactured for a wide range of Bond Thickness t (from 0.05mm to 10mm) and fracture tests conducted under static load. Scanning electron microscopy (SEM) was used to examine the fracture surface morphology. A large deformation elastic- plastic finite element model was developed to evaluate the J-integral value for different Bond Thickness. The fracture energy, Jc , was found to be highly dependent on the Bond Thickness and was lower than that of the bulk adhesive. As the Bond Thickness was increased Jc also increased, though not monotonically, towards the fracture energy of the bulk adhesive. This result was caused by the complicated interactions between the stress and strain fields, plastic deformation of the adhesive around the crack tip, constraint from the adherends and the failure path. I...
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mode l fracture behaviour of adhesive joints part ii stress analysis and constraint parameters
Journal of Adhesion, 1995Co-Authors: Hamid Reza Daghyani, Yiuwing MaiAbstract:Abstract The constraint effect on the fracture behaviour of a rubber-modified epoxy was investigated using compact tension (CT) adhesive joints. An elastic-plastic finite element analysis was conducted to evaluate the stress distribution ahead of the crack tip in the bulk adhesive and adhesive joints of different Bond Thickness. The models with sharp and finite radius crack tips were evaluated in the analyses. The constraint effect of adherends on the stress triaxiality ahead of the crack tip in the adhesive joints were discussed. The constraint parameters were investigated using the J-Q theory and the J-CTOD relationship. It was found that as the adhesive Thickness was increased, the stress triaxiality ahead of the crack tip was relieved by the remarkable deformation of the adhesive material. Similarly, the crack tip constraint was reduced with increasing Bond Thickness so that the fracture energy increased towards the value of the bulk adhesive. A higher constraint was associated with a lower fracture e...