Capability of Single-Sided Transient Thermographic Imaging Method for Detection of Flat Bottom Hole Defects in High-Temperature Composite Materials

摘要

A portion of the development effort for high temperature composite materials is dedicated to the assessment of nondestructive evaluation (NDE) technologies for detecting flaws in these materials [1,2]. To illustrate the importance of defect detection and characterization, figure l(a) shows the results of a delamination sensitivity analysis on a CMC material in consideration for use as a hot section material in advanced aircraft engines. The study indicates that as the size of delaminations increases from 3×3 mm to 25×25 mm, the hot surface temperature increases up to 50 percent making the material unusable for hot section application. Recent technological advancements in infrared camera technology and computer power have made thermographic imaging systems worth evaluating as a nondestructive evaluation tool for advanced composites. Thermography offers the advantages of real-time inspection, no contact with sample, non-ionizing radiation, complex-shape inspection capability, variable field of view size, and portability. The objective of this study was to evaluate the ability of a thermographic imaging technique for detecting flat-bottom hole defects of various diameters and depths in 4 composite systems of interest as high-temperature structural materials. The technique used in this study utilized high intensity flash lamps to heat the sample located on the same side of the detecting infrared camera. The composite systems were (fiber/matrix): silicon carbide/calcia-alumina-silica (SiC/ CAS) CMC, silicon carbide/silicon carbide (SiC/SiC) CMC, silicon carbide/titanium alloy (SiC/Ti) MMC, and graphite/polyimide PMC. The holes ranged from 1 to 13 mm in diameter and 0.1 to 2.5 mm in depth in samples approximately 2 to 3 mm thick. Ultrasonic and radiographie images of the samples were obtained and compared with the thermographic images.