Browsing by Author "Lomov, Stepan Vladimirovitch"
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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 Fatigue tensile behavior of carbon/epoxy composite reinforced with non-crimp 3D orthogonal woven fabric(Elsevier Science, 2011-11-14) Lomov, Stepan Vladimirovitch; Bogdanovich, Alexander E.; Verpoest, Ignaas; Karahan, Mehmet; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksek Okulu.; AAK-4298-2021; 8649952500An experimental study of the in-plane tension-tension fatigue behavior of the carbon fiber/epoxy matrix composite reinforced with non-crimp 3D orthogonal woven fabric is presented. The results include pre-fatigue quasi-static test data, fatigue life diagrams, fatigue damage progression, and post-fatigue quasi-static test data for the warp- and fill-directional loading cases. It is revealed that the maximum cycle stress corresponding to at least 3 million cycles of fatigue life without failure, is in the range of 412-450 MPa for both loading directions. This stress range is well above the static damage initiation threshold and significantly above the first static damage threshold (determined by the onset of low energy acoustic emission). The second static damage threshold, determined by the onset of high energy acoustic emission and related to the appearance of local debonds and intensive transverse matrix cracking falls within this range. The established correlation between a 3000,000 cycle fatigue stress limit on one side and the second static damage threshold stress on the other is of a high practical importance, because it will significantly reduce the amount of future fatigue tests required for this class of composites. Surprisingly, for equal maximum cycle stress level, the fatigue life under fill-directional loading appears about three times shorter than that under warp-directional loading. The 100,000 cycle, 500,000 cycle and 1000,000 cycle fatigue loading with 450 MPa maximum cycle stress has resulted in so high variations of post-fatigue static modulus, strength and ultimate strain, that no consistent and statistically meaningful trends could have been established; further extensive experimental studies are required to reliably quantify this effect. (C) 2011 Elsevier Ltd. All rights reserved.Item Internal geometry evaluation of non-crimp 3D orthogonal woven carbon fabric composite(Elsevier, 2010-09) Lomov, Stepan Vladimirovitch; Bogdanovich, Alexander E.; Mungalov, Dimitri; Verpoest, Ignaas; Karahan, Mehmet; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500Measurements of the internal geometry of a carbon fiber non-crimp 3D orthogonal woven composite are presented, including. waviness of the yarns, cross sections of the yarns, dimensions of the yarn cross sections, and local fiber volume fraction. The measured waviness of warp and fill yarns are well below 0.1%. which shows that the fabric termed here "non-crimp" has nearly straight in-plane fibers as-produced, and this feature is maintained after going through all steps of fabric handling and composite manufacturing The variability of dimensions of the yarns is in the range of 4-8% for warp and fill directions, while the variability of the yarn spacing is in the range of 3-4%. These variability parameters are lower than respective ranges of variability of the yarn waviness and the cross-sectional dimensions in typical carbon 2D weave and 3D interlock weave composites, which are also illustrated in this work for comparison.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.