Civil Engineering / İnşaat Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/13

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Access type: Open accessSubject: search.filters.subject.Delamination

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  • Article
    Citation - WoS: 39
    Citation - Scopus: 40
    Mode-I Fracture Toughness of Carbon Fiber/Epoxy Composites Interleaved by Aramid Nonwoven Veils
    (Techno Press, 2019) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, Engin
    In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of 8.5 g/m(2) to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites.
  • Article
    Citation - WoS: 97
    Citation - Scopus: 110
    Effect of Polyamide-6,6 (pa 66) Nonwoven Veils on the Mechanical Performance of Carbon Fiber/Epoxy Composites
    (Elsevier Ltd., 2018) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, Engin
    In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 5
    The Influence of Low Energy Impacts on the Static and Dynamic Response of a Foam Core Composite Wing
    (SAGE Publications Inc., 2009) Aktaş, Engin; Seaver, Mark; Nichols, Jonathan M.; Trickey, Stephen T.; Davis, W. R.
    This work describes damage detection efforts on a composite wing subject to a series of low-energy (ĝ̂1/47 J) impacts. Two airfoils with fundamentally different damage scenarios were considered. The first damage scenario produced no visible signs of damage on the wing surface following eight impacts. A duplicate wing, subjected to a similar series of impacts, was investigated using flash thermography and subsequently autopsied. The flash thermography showed small, localized damage in the skin, but gave no information about core damage. The autopsy showed core/skin disbonding at both interfaces that varied with the number of impacts, core crushing, and a through the core shear crack. No clear changes to the static or dynamic wing response were observed for this scenario. The second damage scenario involved cracking of the wing skin. While damage quantification was not undertaken for this scenario, both static and dynamic changes in wing response were observed. An analytical model of the wing is presented which helps explain the observed behaviors of the two damage scenarios.