Browsing by Author "Verpoest, I."
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Item Compressibility of CNT-grafted fibrous reinforcements: A theory(Springer, 2010-04) Lomov, Stepan Vladimirovitch; Koissin, Vitaly; Godara, Ajay; Gorbatikh, Larissa; Verpoest, I.; Karahan, Mehmet; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500The paper introduces a theoretical model of compressibility of a nanotube forest with randomly oriented nanotubes, which is applied to predict compressibility of a fibrous reinforcement with CNT-grafted fibres. It is shown that the pressure needed to achieve the target fibre volume fraction of the perform increases drastically when CNT are present in the preform. This can lower the achievable fibre volume fraction for economical vacuum assisted light-RTM manufacturing techniques and increase the pressure requirements in autoclave processing. The modelling is complemented with experimental investigation of compressibility of woven carbon performs with CNT grown on the carbon twill 2/2 fabric using CVD method.Item Internal structure, mechanical properties and damage behaviour of non-crimp 3D orthogonal woven composites(World Acad Union-World Acad Press, 2010) Lomov, Stepan Vladimirovitch; Bogdanovich, Alexander E.; Mungolav, Dimitri D.; Verpoest, I.; Karahan, Mehmet; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu/Tekstil, Giyim, Ayakkabı ve Deri Bölümü.; AAK-4298-2021; 8649952500The paper presents the results of a thorough study of internal structure and mechanical behavior of non-crimp 3D orthogonal woven carbon/epoxy composites. The following parameters and phenomena are investigated: -internal geometry of the reinforcement: shape of the yarns, waviness, dimensions and shape of the cross sections, and fiber volume fraction inside the yarns; -stiffness and strength of the composites; -non-Hookean effects (stiffening of the carbon fibers with increasing strain) -damage initiation and development monitored by means of acoustic emission -crack morphology at different stages of loading studied with X-ray and optical microscopy; -tension-tension fatigue: S-N curves and damage development with increasing number of cycles.Item Monitoring of acoustic emission damage during tensile loading of 3D woven carbon/epoxy composites(Sage Publications, 2014-08) Lomov, Stepan Vladimirovitch; Bogdanovich, Alexander E.; Verpoest, I.; Karahan, Mehmet; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu/Teksti, Giyim, Ayakkabı ve Deri Bölümü.; AAK-4298-2021; 8649952500Registration of acoustic emission (AE) events during tensile loading of fiber-reinforced composites allows the damage caused by these events to be defined and monitored, including damage initiation and progression thresholds. It also provides frequency-based recognition of different types of damage and comparison of its intensity in materials with different reinforcement architectures. The paper reports results of AE registration for 3D non-crimp orthogonal woven (3DNCOW) carbon/epoxy composites. The observed repeatability and spatial distribution of AE events confirm that damage initiation and development are uniform over the tensile sample. The damage characterization by AE is compared with the morphology of damage observed on the specimen cross-sections at characteristic stages of the damage development. The main parameter distinguishing damage mode obtained from the AE registration is the AE energy. It has however been found that the peak frequency of the AE events does not correlate directly with the sequence of the observed damage modes. AE events of high peak frequency, assumed to be related to fiber fracture, suggest that it starts at a later stage than predicted by the Weibull statistics of fiber strength.