Tracing visual and acoustic signatures of mechanical behavior of composite materials
Yılmaz, Bengisu (2017) Tracing visual and acoustic signatures of mechanical behavior of composite materials. [Thesis]
Fiber-reinforced advanced composite materials are widely used in applications of various engineering fields such as aerospace, marine, transportation, and energy. They offer high stiffness and strength along with substantial weight saving potential and allow intriguing design options for superior performance. Despite their remarkably growing use and adaptation into engineering design, the complexity of mechanical behavior of the composite materials, in particular strength and failure, is still a challenge leading to broadening research efforts. This thesis is an effort to address how composite engineers can associate the material characteristics and mechanical behavior of composites using visual and acoustic imaging/recording. Two case studies of structural laminated composites exemplify the potential use of the information obtained specifically from, micro-computed tomographic imaging and general purpose microphone recordings supplemented by video microscopy to seek their correlations with the traditional mechanical test data. The first case focused on the effect of meso-architectural, self-arrangement of fiber bundles with different yarn numbers on the mechanical behavior of non-crimp glass fiber reinforced composites. The visual inspection of anomalies (like the void presence) and in-situ deviations from ideal yarn structures are characterized by using micro-focus computed tomography. Results reveal that the yarn number is directly affecting the tensile behavior of composites in terms of bundle/inter-bundle size, micro-void presence, waviness, and crimping. The second case study aims to show how basic mechanical testing can be supplemented by a general purpose noise reducing microphone and video microscope. The method is simple, affordable, easy to incorporate, yet capable of collecting useful information. The acoustic signatures of the six different cross-ply orthotropic carbon fiber reinforced composites are investigated. In-situ characterization of the progressive failure events is presented as minor, intermediate, major and ultimate with unique sound profiles.
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