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عنوان فارسی مقاله:
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عنوان انگلیسی مقاله:
Thickness dependence of mode I interlaminar fracture toughness in a carbon fiber thermosetting composite
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Interlaminar delamination in laminated composites is one of the primary failure mechanisms in different structural components [1]. In general, the development of a crack in a multi-directional laminate leads to a mixed mode fracture condition that is characterized by different crack propagation scenarios [2,3]. The interlaminar delamination subjected to Mode I loading provides the weakest fracture mode in laminated composite materials. The associated value of the fracture toughness in a unidirectional laminate is commonly measured following a standardized test procedure [4]. The standard defines a recommended configuration of a double cantilever beam (DCB) sample [4,5]. From the material characterization point of view it is desirable to have a testing procedure which is easy to conduct and yields consistent data. To ensure that the measured property in a DCB experiment is a true material constant, a great deal of work focused on examining how critical energy release rate, GIC, in thermosetting [6] and thermoplastic composites [7] depends on crack length, sample width [8], sample thickness [8–10] and thickness of the insert [6], as well as displacement rate [11] and load introduction [4]. The standard suggests using a non-adhesive insert, such as a polytetrafluoroethylene (PTFA) film, which works as a crack initiator, yielding consistent results in comparison with precracked samples [6]. The current ASTM standard recommends using the laminate thicknesses in the range of 3–5 mm, since some early experimental results that used compliance calibration methods did not find fracture toughness dependence on the laminate thickness in unidirectional DCB [8–10]. The standard ASTM procedure is concerned with measuring the initiation and propagation values of fracture toughness. A recommended scheme for data reduction is based on a modified beam theory or compliance calibration [4,5], which account for the finite rotation that occurs at the crack front. The recommended approaches suggested by the standard use subsequent crack propagation data from the initial insert. However, with crack propagation initially straight crack front develops curvature due to the anticlastic bending of a plate composing upper and lower halves of a DCB sample [12–14]. Therefore, applying beam model to describe DCB behavior results in the discrepancy between the data reduction scheme and the physical experiment [15]. Curved crack after propagation is a result of a non-uniform distribution of the energy release rate across the sample width during crack initiation [12,14,16]. Not accounting for crack curving in compliance calibration results in an effectively smaller cracklength than when assuming a straight crack front, which will likely result in overestimation of the strain energy release rate [15]. Furthermore, the distribution of GI across the sample width is a function of sample geometry, and the shape of the curved crack front changes as the crack propagates making the determination of a single crack location ambiguous, due to its curved thumbnail shape [12,13]. Another source of discrepancy introduced with crack propagation is the effect of fiber bridging as a result of fiber migration between the adjacent plies during the early stages of manufacturing [4,17]. Fiber bridging leads to the increase of apparent fracture resistance with subsequent crack propagation from a crack starter (the so called R-curve). In light of these concerns it was the objective of this work to investigate the effects of the laminate thickness on initiation critical energy release rates from the straight PTFE insert without using crack propagation data, as opposed to previous experimental studies which included propagation values of GIC using compliance calibration method [8–10]. The 2D finite element analysis of DCB sample allowed to avoid the built-in cantilever boundary condition imposed by the simple beam theory and effectively accommodated finite rotations at the crack front typically accounted by the ASTM recommended data reduction methods. Four groups of DCB samples were tested with thicknesses in the range of 2 mm to 8 mm to obtain the initiation values of GIC. The beam theory and 2D plane strain finite element analysis of DCB samples were used to calculate fracture toughness and yielded a trend of decreasing GIC with increasing laminate thickness. Therefore, a thinner DCB specimen overestimates the fracture resistance of a thicker laminate in terms of the critical energy release rate or stress intensity factor, which are parameters of linear elastic fracture mechanics (LEFM). Only the fracture toughness at crack initiation was measured. To explain the experimentally found differences, the framework of LEFM was used with the emphasis on the K-dominance concept [18–21]. LEFM was shown to work well for materials exhibiting brittle fracture. Such materials are found among engineering plastics and include some thermoplastics as well as thermosetting resins. The incorporation of the K-dominance idea into LEFM assumes that fracture toughness for any brittle material is defined not only by the critical value of the stress intensity factor, which describes the singular opening stress component [22], but rather the full opening stress field, which can differ significantly from the former. The full stress field is described by the Williams series expansion [23], and in addition to the square root singular term it provides higher order terms present in the solution. The idea of incorporating these higher order terms for better describing the fracture behavior of materials was introduced early by Irwin [22]. Irwin suggested using the first non-singular stress term, constant normal stress in the plane of the crack, denoted later as a T-stress, as a second parameter to include the influence of test configurations. This idea was further developed to qualitatively introduce the influence of T-stress on the stability of crack propagation direction [24] and the applicability under the assumption of small scale yielding [25,26]. The second non-singular stress component present in the opening stress solution was considered in a similar manner to determine the role of the sample configuration on the apparent fracture toughness in Mode I conditions for polymethyl methacrylate (PMMA) [27,28], which is known to exhibit brittle fracture behavior due to a small fracture process zone [29].
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کلمات کلیدی:
Interlaminar Fracture Toughness of Carbon Fiber/Epoxy Composites ... onlinelibrary.wiley.com/.../(SICI)1099-1581(199706)8:6%3C371::AID-PAT658%3E3.... by BY Park - 1997 - Cited by 13 - Related articles Abstract. Mode I (GIC) and Mode II (GIIC) interlaminar fracture toughness of carbon-fiber/epoxy composites have been investigated as a function of the amount of ... Composite Standards - ASTM International https://www.astm.org/Standards/composite-standards.html ASTM composite standards contain tests for the characterization of high ... composite plates and bars, fiber reinforced metal matrix composites, carbon ... D7750 - 12 · Standard Test Method for Cure Behavior of Thermosetting ... Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites. composites - Deep Blue https://deepblue.lib.umich.edu/bitstream/handle/2027.42/.../mower_EFM_87.pdf?...1 by T Mower - 1987 - Cited by 18 - Related articles SHORT FIBER REINFORCED THERMOSET RESIN. COMPOSITES. TODD M. ... Abstract-The fracture toughness characterization of random fiber reinforced polymer composites has been ..... reinforced with fibers of glass and carbon[21]. TOUGHNESS CHARACTERIZATION OF CARBON ... - iupac https://www.iupac.org/publications/pac/63/11/1609/pdf/index.html The fracture mechanics parameters for assessing toughness provides ... Continuous carbon fibre reinforced thermoplastic composites have been under ... [PDF]Toughening of carbon fibre reinforced polymer composites with rubber ... www.expresspolymlett.com/letolt.php?file=EPL-0006743&mi=c the fracture toughness of advanced composite lami- ... lonitrile butadiene rubber (NBR-NP) on the interlaminar shear strength and fracture toughness of carbon fibre reinforced ...... Epoxy/anhydride thermosets modified with end-capped. [PDF]Fracture Toughness of Glass-Carbon (0/90)s Fiber Reinforced ... file.scirp.org/pdf/JMMCE20110800001_16288215.pdf by PSS Gouda - 2011 - Cited by 7 - Related articles Also, using a hybrid composite that contains two or more types of fiber, the advantages of one ... thermosetting composite material. For this ... Fracture toughness test for Glass-carbon reinforced epoxy composite was carried out as per. ASTM D ... Searches related to fracture toughness in a carbon fiber thermosetting composite what is carbon fibre carbon fiber properties carbon fiber reinforced polymer carbon fiber material carbon fibre structure carbon fiber uses carbon fiber strength carbon fiber composite
