UBC Theses and Dissertations
Toward better understanding of mechanical response of fabrics under multiple combined loading modes : experimental and statistical analysis Sultana Mir, Samia
Fabric reinforced composites are becoming among primary materials of choice in manufacturing damage tolerant aerospace, automotive, and naval architectural parts. Detailed characterization of fabric reinforcements, however, is necessary to ensure the quality of such composite part and to prevent structural failure during their service. A number of experimental studies have been dedicated in the past to characterize the deformation of fabrics under individual loading modes, such as pure uniaxial tension, pure biaxial tension and pure shear. There still exists, however, a lack of knowledge and standardization in testing and analyzing the mechanical response of fabrics under combined shear-tension loadings, both in simultaneous and sequential modes. Moreover, in reality, there are sources of uncertainties in the forming of these multi-scale fibrous materials, which often results in non-repeatable test data and causes inconsistencies for full characterization. Recognizing the above gaps, the aim of this thesis has been to design, conduct, and analyze a set of experiments for enhanced characterization of a typical glass fabric under select individual and combined shear-biaxial tension loading modes. The experimental tests were performed using a new fixture recently designed and manufactured by the Composites & Optimization Laboratory at UBC and its international partners. On the account of inherent material uncertainties, all tested deformation modes were analyzed and compared via a series of ANOVA analysis. Results showed that statistically there were significant differences between the warp and weft responses of the fabric under all the deformation modes, with weft yarns being generally stiffer. The shear-tension coupling effect in combined deformation modes yielded higher normal axial and shear forces compared to the individual deformation modes. More severe local damage zones were observed during the coupling tests. Finally, a Digital Image Correlation test was conducted to inspect wrinkling in the deformed specimens. Under a pure shear mode, some out of plane wrinkles appeared due to misalignment, whereas in the simultaneous loading condition it was nearly disappeared, thanks to the presence of fiber tension.
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