Abstract Mode II fracture toughness tests for a type of double-lap joint referred to as the doubly end notched tension (DENT) tests were validated by experimental and numerical approaches. Crack growth behavior of two cracks was simultaneously observed during fracture toughness tests and analyzed by the digital image correlation (DIC) method. As one of the two cracks propagated first and the other followed, finite element (FE) analyses were carried out to clarify the mechanisms. The results of FE analyses showed that mode II energy release rate at the extended crack tip increased at the beginning of crack growth, and subsequently decreased under constant displacement condition. An opposite trend was found at the other crack tip. One cause of this phenomenon was due to local bending of the specimen. The effects of the geometry of specimens were also discussed. The FE analyses also revealed that the ratio of middle layer thickness to the outer layers thickness significantly affects the crack growth behavior in the DENT specimens.
Last. Kwek Tze Tan(University of Akron)H-Index: 15
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Abstract Microscopic failure mechanisms in adhesively bonded joints of carbon fiber reinforced polymer (CFRP) structures were studied, and in-situ observation during fracture toughness tests under mode I and mode II loading were carried out. Strain in the adhesive layer was quantitatively evaluated by applying the digital image correlation (DIC) method to micrographs. Strain concentration was observed along the CFRP/adhesive interface under mode I loading. On the other hand, strain concentration...
Last. Akinori Yoshimura(JAXA: Japan Aerospace Exploration Agency)H-Index: 12
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Quantitative determination of interlaminar fracture toughness that governs onset and growth of delamination is essential for engineering of composite materials and structures. This study proposes a new approach to evaluate both the initial fracture toughness and the crack growth resistance property of pure mode II delamination by tensile tests of specimens having two initial cracks, which were conceived from double-lap joints. The proposed test method achieves stable growth of mode II delaminati...
A compression test of a unidirectional carbon fiber reinforced plastic (CFRP) rectangular coupon was performed in an X-ray computed tomography (CT) system. Internal compressive failure of the CFRP was observed under loading. Two-dimensional fiber microbuckling developed non-uniformly in the specimen, and enlarged locally at one side. Fiber failure then initiated at the side edge and propagated through the whole cross section. A two-dimensional kink-band developed as a result of two-dimensional f...
#1S. K. Panigrahi(North Eastern Regional Institute of Science and Technology)H-Index: 12
#1Simanchalo Panigrahi(North Eastern Regional Institute of Science and Technology)H-Index: 24
Last. B. Pradhan(IIT-KGP: Indian Institute of Technology Kharagpur)H-Index: 14
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Abstract Three-dimensional non-linear finite element analyses have been carried out for graphite/epoxy laminated FRP composite double lap joints (DLJ) to study the onset and growth of adhesion failure and delamination induced damages. Out-of-plane stresses on different interfacial surfaces of the DLJ have been determined. The peel and shear stress distributions in the adhesive layer have been evaluated and compared with the existing analytical and numerical solutions showing good agreement. Tsai...
#2A.J. Brunner(Empa: Swiss Federal Laboratories for Materials Science and Technology)H-Index: 7
Last. J. G. Williams(Imperial College London)H-Index: 55
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Abstract A number of technical issues have slowed the progress towards an agreed mode II test protocol for composite laminates and perhaps the most important of these has concerned the difficulty in measuring crack length during the test. In this paper, we extend a previous analysis which was developed for mode I delamination cases where significant bridging and micro-cracking occurred. The approach utilises an effective crack length and if successful, may eliminate the need to measure this para...
#1Till Vallée(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 23
#2João R. Correia(Technical University of Lisbon)H-Index: 34
Last. Thomas Keller(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 45
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Experimental and numerical investigations were carried out on adhesively bonded full-scale double lap joints composed of pultruded GFRP profiles with relatively thick adhesive layers. Thick adhesive layers are often used in infrastructure applications in order to compensate for geometrical tolerances. The influence of different geometric parameters on the joint strength was investigated: the thickness of the adhesive layer (5-35mm), the fillet radius (2-10mm) and the overlap length (100-300mm). ...
Linear and nonlinear finite element analyses are used to examine the effects of friction, test geometry, and fixture compliance on the perceived toughness as obtained from three- and four-point bend end-notched flexure tests. To this end, a newly developed 'direct energy balance approach' is used to obtain the 'true' energy release rate for any given specimen, test geometry, and coefficient of friction. Finite element analyses are also used in a simulated compliance calibration technique, which ...
#2Liyong Tong(USYD: University of Sydney)H-Index: 61
Last. Jie Jin Wang(DST: Defence Science and Technology Organisation)H-Index: 1
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Abstract This paper presents an analytical model for understanding crack propagation behaviour of adhesively bonded cracked double-lap shear joints subjected to tension–tension fatigue loading. The analytical model can be used to calculate the bending moments at the cross sections of the crack tips and strain-energy release rates at the two crack tips. The accuracy of the analytical model is established by comparing the calculated bending moments and energy release rates with those predicted usi...
Results are presented from a study to determine the most appropriate crack length measurement and data reduction techniques for use with the four-point bend end-notched flexure test. Using two different graphite/epoxy materials, the variability in crack length measurements due to different observers and/or measurement techniques, including visual observation and ultrasonic inspection, and their effects on the perceived values of the mode II delamination toughness, GIIc, were evaluated for two di...
Abstract null null In mode II interlaminar fracture toughness tests of composite laminates, the fracture toughness evaluated based on linear elastic fracture mechanics deviates from the true toughness due to the material nonlinearity of the matrix. In this study, an elastoplastic finite-element analysis was performed on a new quasi-static mode II interlaminar fracture toughness test, i.e., the doubly end-notched tension (DENT) test, to investigate the difference between the perceived energy rele...
#1A. Wagih(KAUST: King Abdullah University of Science and Technology)H-Index: 19
#2Ran Tao(KAUST: King Abdullah University of Science and Technology)H-Index: 8
Last. Arief Yudhanto(KAUST: King Abdullah University of Science and Technology)H-Index: 14
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Abstract The mode II fracture toughness of secondary bonded joints can be improved by creating tailored sacrificial cracks inside the adhesive. To this end, we inserted a PTFE film inside the adhesive bondline during the bonding process to create sacrificial cracks inside the adhesive. We demonstrated the efficiency of this technique through ENF tests that characterize mode II fracture toughness of adhesive-bonded CFRP adherends. We ascribed the improvement in toughness to the reduction of the s...