X-Ray Measurement and Porosity in Graphite/Polyimide Composites

Abstract

One of the persistent problems in the control of quality in materials used in structures is that of porosity. Whether the material is a casting, an epoxy composite, or a complex ceramic or metal matrix composite, the presence of porosity, depending upon the severity, causes a degradation of the parts performance characteristics and their longevity. The detection of porosity in many industries is important in two ways, namely, in material quality control and in monitoring process control (1). One class of materials where both of these problems arise is the graphite composites (2–4). To date, the inspection of these composites using an X-ray method has been unsatisfactory in that the film methods frequently tried did not have the sensitivity resolution to yield a quantitative measure of the porosity volume percent. Such a measure becomes even more critical in ceramic composites in that the difference between a good material and a poor one is a level of porosity rather than the presence of porosity, as is the case in graphite epoxy composites. We wish to report results of an X-ray method to measure porosity in materials using the graphite polyimide composites as an example. The method is certainly not restricted to this type of graphite composite or indeed to graphite composites.