Fiber Orientation Measurement in Platelet-Based Composites via Computed Tomography Analysis
Abstract
Platelet-based composite material systems are cut and slit from pre-impregnated, fiber reinforced, unidirectional tape to facilitate molding of complex geometries and retain a portion of the parent material performance. Parts compression molded from uncontrolled initial charges of these material systems have a heterogeneous internal structure including fiber collimation within platelets, discontinuities at platelet boundaries, and generally uncontrolled final platelet orientation states. Such a large degree of variability in intra- and inter-part mesostructure requires characterization of entire parts, both to inform simulations of part performance and to validate simulation results of the manufacturing process. Acquiring whole-specimen microstructural data for complex, bracket-like geometries at a resolution useful for analysis presents a challenge for existing inspection methods, such as microscopy. Computed tomography (CT) scans can provide whole-specimen local density data nondestructively, but for the scan volume sizes inspected here, the resulting 15-50µm voxel size is larger than the sub-fiber diameter (microscale) resolution that is normally required to determine fiber orientations. However, because microscopy shows that individual platelets remain as intact fiber bundles in this investigation, a mesoscale resolution CT approach provides sufficient local density information to determine fiber bundle orientation, and therefore the internally aligned fiber orientation. In this manner, the whole-specimen local fiber orientation is determined with a degree of detail that is useful to the engineer attempting to characterize heterogeneous material systems like the compression molded, AS4/PEKK unidirectional platelets inspected here. Microscopy of three unique geometries is performed to characterize the apparent micro- and mesostructure of this material system and to provide baseline measurements of orientation state for validation of the CT orientation analysis method presented.
Degree
Ph.D.
Advisors
Pipes, Purdue University.
Subject Area
Aerospace engineering|Materials science
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