Computed tomography of composites

The majority of composite architectures are inherently heterogeneous in three dimensions (3D), and accumulate damage in complex 3D patterns. Historically, materials examination has mainly relied on the use of two-dimensional techniques, such as optical and scanning electron microscopy, where the critical sample cross-sections are identified and cut out. The three-dimensional nature can then only be inferred from limited orthogonal views, or by serial sectioning. Such methods have significant limitations: being destructive, prone to introducing artifacts and vulnerable to misinterpretation in 3D, or of missing key defects altogether. These disadvantages have driven researchers to consider nondestructive techniques for material inspection. Various nondestructive techniques have been employed to detect damage in composites including ultrasonic imaging (C-scan), primarily to evaluate manufacturing defects or delamination often associated with impact damage; acoustic emission to monitor the formation and growth of damage, particularly fiber fracture; thermography and thermo-elastic stress analysis to correlate damage and surface strains. These methods have intrinsic limitations, particularly the inability to provide unambiguous information on the type, size and orientation of damage simultaneously. Furthermore, these techniques often fail to resolve fine-scale failure events (e.g., fiber/matrix debonding), are sensitive only to certain types of damage (e.g., fiber fractures), or cannot provide a detailed 3D representation of damage. In view of these shortcomings and continuing improvements in spatial resolution, X-ray computed tomography (CT) has become established as a powerful technique for multiscale (macro-, meso-, micro- and nanoscale) imaging of composite architectures, manufacturing defects, and in-service damage. Further, as a nondestructive technique it also opens....