Region-of-Interest X-Ray Tomography for the Non-Destructive Characterization of Local Fiber Orientation in Large Fiber Composite Parts

To detect and characterize materials defects in fiber composites as well as for evaluating the three-dimensional local fiber orientation in the latter, X-ray micro-CT is the preferred method of choice. When micro computed tomography is applied to inspect large components, the method is referred to as region-of-interest computed tomography. Parts can be as large as 10 cm wide and 1 m long, while the measurement volume of micro computed tomography is a cylinder of only 4 − 5 mm diameter (typical wall thickness of fiber composite parts). In this report, the potentials and limits of region-of-interest computed tomography are discussed with regard to spatial resolution and precision when evaluating defects and local fiber orientation in squeeze cast components. The micro computed tomography scanner metRIC at Fraunhofer's Development Center X-ray Technology EZRT delivers region-of-interest computed tomography up to a spatial resolution of 2 mm/voxel, which is sufficient for determining the orientation of natural or synthetic fibers, wood, carbon and glass. The mean local fiber orientation is estimated on an isotropic structuring element of approximately 0.1 mm length by means of volume image analysis (MAVI software package by Fraunhofer ITWM). Knowing the exact local fiber orientation is critical for estimating anisotropic thermal conductivity and materials strength.