Non-destructive examination of ceramic matrix composites for quantitative determination of porosity via pulse-echo thermographic inspection

Abstract

Ceramic Matrix Composites are seeing a widespread increase in use, especially in the aerospace industry. These materials are being utilized for their excellent material properties at high temperatures. As these materials are used in jet engine components and proposed as the skins of hypersonic vehicles, the consequences of material failure can be catastrophic. As-manufactured porosity is one of the earliest indicators of sub-optimal material properties that would lead to premature failure. Non-Destructive Testing methods have long been utilized for the examination of more “traditional” composite materials. This investigation discusses the use of several NDT methods on CMCs and the advantages and limitations of those inspection methods, with a particular focus on the determination of sample porosity. Pulse-Echo Flash Thermographic Inspection is of particular focus, while Film Radiography and Computed Tomography are also examined. Derived equations are examined for Film Radiography and Flash Thermography to determine their accuracy in calculating porosity from raw data. While Film Radiography did not yield a suitable equation, Flash Thermographic results yielded an equation which allowed for calculation of the sample porosity using only the raw data and known sample thickness. This equation was partially validated using results from additional sample sets. The additional limitations and artifacts of Flash Thermography are examined to show the ways in which the inspection method is limited. Examinations of representative aircraft components, manufactured of CMC material, also provided realistic defects and integrated components that were located by and had varying effects on the Flash Thermographic Inspection.