Quantitative microradiography and its applications to microdamage assessment

A state-of-the art microradiographic system including an imaging chain and a micro-focus X-ray source has been used for development of a quantitative nondestructive evaluation (NDE) tool in characterizing material microdamages. In contrast to conventional radiographic systems, where the performance is well understood, there is limited scientific data available for the evaluation of microradiographic system performance in terms of the effect of projection magnification and the geometric unsharpness on system detectability. Evaluating the detectability of a microradiographic system is a further challenge in this research. Quantitative methods are developed to characterize the detectability of a microradiographic system. The concept of optimum magnification and the effect of unsharpness on detectability of the system are studied.; The enlarged and high resolution images are used to develop a microradiographic method for microdamage depth measurement. The method was applied to quantify micro-damage due to pitting corrosion in Al 2024-T3 alloy. The accuracy of the developed technique was then validated using other methods such as comparison with optical microscopy data, comparison with the 3-D images taken by profilometry, direct reading of the thickness lost by cutting the actual corroded samples, radiography of samples with two perpendicular shots, and also quantitative pixel-by-pixel comparison was done between data from profilometry and those from the microradiographic method.; Hidden microdamage in materials is a challenging area for NDE; in order to characterize this sort of damage, the effect of contrast change on detectability was studied and compared with the theoretical predictions.; Also a microradiographic technique has been developed to study initiation, growth and locations of fine primary and secondary cracks in dwell fatigue testing on titanium samples. Microradiographic data then has been compared with in-situ ultrasonic signals for further evaluation.; This research also involves the study of the phase-contrast imaging applicability for microradiographic characterization of damage in structural materials. It has been shown that by optimization of the exposure parameters, the X-ray beam from a micro-focus system can be used as a phase contrast imaging technique in engineering settings. (Abstract shortened by UMI.)...