Abstract The mode-I fracture behavior and non-uniformity coefficient β of an adhesively bonded joint composed of Glass Fiber-reinforced Polymer (GFRP) laminates are investigated using double cantilever beam (DCB) specimens with an adhesive layer. First, the opening displacement of the DCB is solved using the elastic foundation beam method considering the impact of the displacement and the rotation angle of the crack tip. The fracture toughness G Ic is calculated using the compliance method through the critical load ( P c ) obtained from the experiment. During the crack growth in the experiment and in the finite element analysis, a thumbnail-shaped front is observed, which demonstrates that the energy release rate (ERR) is unevenly distributed along the transversal direction. Next, a practical formula for β as a function of the parameters a / b (crack length/width) and n (number of plies) is put forward, which can be applied to DCB specimens composed of isotropic single-ply plates or anti-symmetric angle-laid laminate plates (each leg). Finally, crack propagation is simulated using a modified G Ic ∗ , which includes the non-uniformity coefficient β , from which the simulated P c is in good agreement with the experimental results.
Abstract Mode I cohesive laws of carbon–epoxy composite bonded joints were obtained using the direct method applied to the double cantilever beam test. This method is based on the differentiation of the relation between the evolution of the strain energy release rate and the crack tip opening displacement (CTOD) during the test. An equivalent crack length method was used to obtain the strain energy release rate evolution. Following this procedure, several drawbacks inherent to crack length monit...
#1V. Cooper(UCD: University College Dublin)H-Index: 3
#2Alojz Ivankovic(UCD: University College Dublin)H-Index: 23
Last. Neal Murphy(UCD: University College Dublin)H-Index: 18
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Abstract The current work is a combined experimental-numerical study of the fracture behaviour of a nano-toughened, structural epoxy adhesive. The mode I fracture toughness of the adhesive is measured using tapered double-cantilever beam (TDCB) tests with various bond gap thicknesses ranging from 0.25 mm to 2.5 mm. Circumferentially deep-notched tensile specimens are independently employed to measure the cohesive strength of the adhesive as a function of constraint. The experimental TDCB test re...
#1Mahmood M. Shokrieh(IUST: Iran University of Science and Technology)H-Index: 53
#2M. Heidari-Rarani(IUST: Iran University of Science and Technology)H-Index: 16
Last. S. Rahimi(IUST: Iran University of Science and Technology)H-Index: 1
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Abstract Mode I delamination toughness ( G Ic ) of a laminated composite depends not only on the stacking sequence or indirectly coupling parameter of D c = D 12 2 D 11 D 22 , but also on specimen geometrical ratios a 0 / b and a 0 / h . In this study, a non-uniformity ratio, β = ( G Imax − G Iavg )/ G Iavg %, is introduced to take into account the influence of above factors on the energy release rate distribution along the width of double cantilever beam (DCB) specimens simultaneously. Results ...
The effect of the addition of carbon nanoreinforcements to an epoxy adhesive on the strength and toughness of carbon fibre/epoxy composite joints was studied. The laminate surfaces, treated with peel ply, were characterised by profilometry, image analysis and wettability. The mechanical properties of the joints were determined by lap shear testing and double cantilever beam testing. The fracture mechanisms were studied by scanning electron microscopy. The addition of carbon nanofibres and carbon...
Last. Thomas Keller(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 45
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The fracture behavior of adhesively-bonded pultruded joints was experimentally investigated under Mode I loading using double cantilever beam specimens. The pultruded adherends comprised two mat layers on each side with a roving layer in the middle. An epoxy adhesive was used to form the double cantilever beam specimen. The pre-crack was introduced in three different depths in the adherend in order to induce crack initiation and propagation between different layers and thus investigate the effec...
Abstract This work covers the problems encountered in correctly determining mode I interlaminar fracture toughness of composite materials. Pure mode I tests were performed on double cantilever beam (DCB) specimens composed by quasi-homogeneous and uncoupled multidirectional (MD) laminates using 16 or 26-ply: [α/−α 2 /α/−α/α 2 /−α] sym or anti-sym and [0/α/−α/0 2 /−α/0/α/0 2 /α/−α/0] sym , with α = 0°,15°,30°,45°,90°. A finite element analysis shows that the non-uniformity ratio β=(G Imax −G Iav....
Last. Thomas Keller(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 45
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The Mode I and II fracture behaviors of adhesively-bonded joints composed of pultruded glass fiber-reinforced polymer (GFRP) laminates were experimentally investigated using Double-Cantilever-Beam (DCB) and End-Loaded-Split (ELS) specimens. The large specimen dimensions on the full-scale level and asymmetric crack propagation in the laminates imposed deviations from the standardized specimens. For crack length measurement, in addition to visual observation, a video extensometer was used. Similar...
#1Martin Schollmayer(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 5
#2Thomas Keller(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 45
The through-thickness performance of adhesive joints connecting pultruded FRP bridge decks and steel girders subjected to loading in the transverse bridge direction was investigated. Deck-to-girder adhesive joints can be assumed as being loaded by uplift forces only (and not by additional bending moments) if the adhesive layer has a minimal thickness of approximately 10 mm. If possible, however, steel web stiffeners should not be connected to the upper flange in order to allow free flange rotati...
Abstract The energy release rate in delamination of angle-ply laminated double cantilever composite beam specimens was calculated using the compliance equation, and interlaminar cohesive strengths were obtained. Instead of the traditional approach of a beam on an elastic foundation, a second-order shear-thickness deformation beam theory (SSTDBT) was considered. The equilibrium equations were obtained using the principle of minimum total potential energy and the system of ordinary differential eq...
This paper proposes a simple, efficient algorithm to trace a moving delamination front with an arbitrary and changing shape so that delamination growth can be analyzed by using stationary meshes. Based on the algorithm, a delamination front can be defined by two vectors that pass through any point on the front. The normal vector and the tangent vector for the local coordinate system can then be obtained based on the two delamination front vectors. An important feature of this approach is that it...
Last. Xiaojing Gong(University of Toulouse)H-Index: 1
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Abstract Strain energy release rate (SERR) along a linear crack front of a multidirectional composite DCB specimen shows an obviously non-uniform distribution, which causes the fracture toughness GIavg measured by experiments smaller than the real GIC, and so leading to a lower estimation of fracture toughness. In this study, based on the numerical model a novel semi-empirical closed-form formula was proposed for determination of pure mode I fracture toughness of a multidirectional composite DCB...
Composite materials are known for their high stiffness and strength at lower weight as compared to conventional structural materials. Recently, there has been a growing interest in finding the new ...
In this study, interfacial fracture toughness was investigated experimentally and numerically in laminated composite plates with different fiber reinforcement angles bonded with adhesive. The composite plates are four-layered and the layer sequence is [0o/θ]s. DCB test was applied to composite plates reinforced with epoxy resin matrix and unidirectional carbon fiber. The experimental sample model for the DCB test was made using the ANSYS finite element package program. In the numerical study, fo...
Abstract This work investigated the evolution of the non-uniform distribution of Mode-I strain energy release rate (SERR) along a straight pre-crack front of double cantilever beams (DCB), caused by the anticlastic deformation and the longitudinal free-edge effects. A modified DCB specimen with a curved pre-crack front was introduced in order to alleviate this problem and produce an uniform SERR distribution at the initiation and propagation stages. The first order optimization method was used t...
Abstract One of the challenges in building a predictive numerical model for laminated composites is the ability to accurately model delamination. In this paper, a modular orthotropic plasticity model that is made of three sub-models – deformation, damage and failure, is used in conjunction with a delamination model to predict the behavior of an impact event involving a unidirectional laminated composite. Both the composite and delamination constitutive models are built entirely using experimenta...
With the development of finite element (FE) codes, numerical modelling of delamination is often considered to be somewhat commonplace in modern engineering. However, the readily available modelling techniques often undermine the truthful understanding of the nature of the problem. In particular, a critical review of the representativeness of the numerical model is often diverted to merely a matter of numerical accuracy. The objective of this paper is to scrutinise the representativeness of cohes...
Abstract Mixed-mode interlaminar fracture behaviour of Glass/Vinylester composite laminate has been investigated numerically and experimentally. In the current study, fracture parameters of this type of material have been obtained in pure mode-I, pure mode-II and mixed-mode loading conditions. For this purpose, the butterfly Arcan specimens were produced with various lengths of delamination as pre-cracks and were tested in various loading conditions. The experiments were conducted using an Arcan...
ABSTRACTThe double cantilever beam specimen has been increasingly employed to enable the development of cohesive zone models for adhesive joints. Evaluation of the traction–separation law (TSL) requires elaborate experimental techniques and usually relies on data measured until the crack initiation point. Nonetheless, current standards stipulate fracture energy measurements under steady-state crack propagation. This paper investigated the influence of the cohesive zone on the commonly used corre...
This experiment studies the mode II fracture behavior of an adhesively bonded joint composed of GFRP laminates. A new beam model is presented to calculate the mode II ERR for GFRP bonded 4-ENF specimens. In this model, the deformation of 4-ENF specimens caused by the relative deflection angle between the upper and lower layers and by the bending deformation of the upper and lower layers, respectively, is introduced; the effect of the adhesive layer deformation is presented. The closed-form analy...