Considerations for nondestructive evaluation of discontinuous fiber composites using dynamic analysis
Knowledge of the composite microstructure is vital to predicting performance of the structural member. However, depending on the manufacturing process, the microstructure of the part may be unknown and not predictable with simulation software. A few non-destructive evaluation techniques have been adjusted to predict fiber orientation of composites, including CT scans and thermography, but none have proven acceptable on a large scale with the amount of fidelity required. This research investigated the use of dynamic analysis as a non-destructive evaluation technique to predict fiber orientation of discontinuous fiber compression molded parts. While the method is currently unable to predict individual fiber orientations, it can indicate the magnitude of change in microstructure, whether local or global. This research also identified several key considerations for testing of heterogeneous anisotropic composites versus their isotropic counterparts. Dynamic properties of a composite part, including natural frequency and mode shape, are dependent upon the geometric symmetry and material symmetry present in the part. Fiber orientation variations within the vicinity of boundary conditions for a test setup have a large impact on the natural frequencies of the first few modes. With the use of the COMAC parameter, analysis can identify the locations on the geometry that will capture the most number of natural frequencies for a given frequency range.
Pipes, Purdue University.
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