Computed Tomography for Non-destructive Inspection of Hot Structures and TPS Components

Kurzfassung

Verifying the quality of a large TPS structure component’s material and therefore providing its flight readiness capability, belongs to one of the most challenging objectives for non-destructive evaluation techniques. Especially when different components of fibre ceramic composites are joined together or attached to other parts of differing materials (e.g. bulk ceramics, metals, insulations, seal elements), it is always of great interest to obtain proper information about the interfaces between these parts. Well known and approved NDE methods such as radiography, ultrasound inspection or lock-in thermography only offer a two-dimensional view of a three-dimensional structure with a projection of all detectable features through the structure’s thickness. This gives way to sometimes quite distinct interpretations of microstructural features and defects. Furthermore, some of these inspection techniques do not allow to scan structural components without using a coupling media such as water or at least a contact gel as used with ultrasound transducers. Other NDE techniques are not suitable to inspect special regions which are located at inaccessible areas as for example the inner side of a curved structure with joined stiffeners as reinforcement elements. Sometimes it is just the penetration depth that is not sufficient to get the necessary information of failure critical areas. However, with X-ray based computed tomography (CT), non-destructive evaluation will be enforced with a powerful tool that provides three-dimensional data with exceptional high resolution. CT inspections allow the detection of flaws such as microcracks, voids and porosity distributions in the microstructure and joining interfaces between different structure components in every part of the structure’s volume. Eight years ago, DLR was successfully using computed tomography for the first time to prove the good quality of the joining interfaces between the X-38 nose cap structure and its CMC load introduction attachments. Because there was no CT available at that time, it was decided to use a medical CT facility at a hospital nearby. Though it was not possible to obtain images of a higher resolution, the interfaces of the outer CMC shell (nose cap) and each load introduction attachment or pressure port plug was inspected in detail. In the meantime, DLR is operating its own CT test facilities for systematic non-destructive material inspections. In the following it is shown how the large CT facility v|tome|x L450 was successfully used for an in-situ evaluation of the load introduction attachments of EXPERT’s CMC nose cap structure.