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Non-Destructive X-ray Computed Microtomography Inspection of Composites Containing Manufacturing Defects



Honeycomb sandwich constructions are used extensively in the aerospace industry to increase stiffness of composite structures without adding significant weight. As part of the manufacturing process, immersion ultrasonic non-destructive inspection (NDI) is typically conducted in order to validate compliance of components. Ultrasonic NDI is relatively cost effective. Attenuation variations from baselines (known good components) indicate non-compliance of manufactured components, but the source of attenuation is often unavailable from ultrasonic inspection. Examples of sources of attenuation of ultrasonic signals include porosity in the bondline or laminate, delaminations between the core and facesheets, and foreign objects that entered the component during manufacturing. In order to improve manufacturing processes and reduce the costs associated with non-compliant components, a relatively new (to composites manufacturing) NDI technique, X-ray computed microtomography (CμT) is used. The advantages and limitations of CμT are discussed via investigation of noncompliant components. Ultrasonic NDI results of non-compliant cored composite aircraft components are presented. Regions of non-compliance are further investigated via CμT. The CμT investigation reveals unanticipated defects, blistering within the honeycomb core cell walls, at the locations that ultrasonic NDI indicated as non-compliant. As part of the CμT process, 3-dimensional digital volumes of the components are created. From these volumes, virtual cross-section cuts are created, including the creation of videos showing the ability to make “infinite” section cuts, which allow defects within the component to be investigated. Finally, results of destructive investigation are presented to confirm the blistering observed via the CμT investigation.

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