Author: Li, Tianzhu
Title: Numerical studies on tensile strength of fiber reinforced composites with rigid impurities and void contents
Degree: M.Sc.
Year: 2015
Subject: Fibrous composites.
Fibrous composites -- Fracture.
Hong Kong Polytechnic University -- Dissertations
Department: Department of Mechanical Engineering
Pages: xi, 80 leaves : illustrations (chiefly color) ; 30 cm
Language: English
Abstract: Carbon fiber reinforced composite has many advantages and has been applied in wide fields, such as aerospace engineering and civil engineering. The microscopic and macroscopic performances of composite have a complex relation and existing research on damage process of composite is not impeccable. So it's necessary to do further research on the prediction of composite strength which is able to explain the complicated damage process. This study is to demonstrate the longitudinal performance of carbon fiber reinforced composite with statistical model and induced stress field method. The single fiber statistical strength is based on Weibull distribution and depends on Weibull parameters and characteristic strength of fiber. Each single fiber has its own strength in a specific failure probability. These microscopic properties determine the macroscopic performance especially the tensile strength of the carbon fiber reinforced composite. In this thesis, longitudinal performance transfer from mesoscopic properties to macroscopic properties has been studied. Meanwhile, this study has demonstrated how void contents and rigid impurities weaken the tensile strength of composite. The main variables which affect composite tensile strength including randomness distribution of single fiber strength, the quantity of void contents and the quantity of rigid impurities. Void contents block the transmission of induced stress field. This makes the stress concentration more serious and leads to the drop of strength. Simulation results show that hyperbola induced stress field method is an efficient way to predict composite tensile strength. 300 equivalent void contents decrease the strength nearly by 10%. The more void contents, the lower strength of composite bundle. The equivalent quantity of void contents doesn't present a linear correlation with tensile strength of composite. Rigid impurities may bend partial fibers. Axial load also causes a transverse strain because of Poission's ratio. However, the transverse stress is low and doesn't reach the yielding stress of fiber so the transverse stress is ignored in this thesis. Bent fibers bear axial load only when the strain reaches a specific value. Results show that, bent fibers caused by rigid impurities can decrease the strength of composite by up to 18%. More bent fibers cause a larger drop of composite strength.
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