Detection of Subsurface Defects Using X-Ray Lateral Migration Radiography - A New Backscatter Imaging Technique

Dugan, Edward T. ; Jacobs, Alan M.

University of Florida, Gainesville, Florida (United States)

关键词: Copper;    Aluminium;    Nondestructive Analysis;    46 Instrumentation Related To Nuclear Science And Technology;    Surface Area;   

DOI  :  10.2172/807646
RP-ID  :  None
RP-ID  :  FG07-00ID13922
RP-ID  :  807646

美国|英语

来源: UNT Digital Library

【 摘 要 】

A new Compton X-ray backscatter imaging technique called lateral migration radiography (LMR) is applied to detecting a class of sub-surface defects in materials and structures of industrial importance. These include flaws and defects for which there is either no known method or an effective method for detection. Examples are delamination in layered composite structures, defects in deposited coatings on metal surfaces such as in aircraft jet engine components and geometrical structural/composition changes (e.g. due to corrosion) on the inside of shell-like components with only outside surface area access.Research efforts include: the construction of simulated flawed test objects on which experimental measurements are performed to establish LMR flaw detection capabilities; performance of Monte Carlo simulations of these measurements to assist in predicting optimum source-detector configurations and to help obtain a detailed understanding of the physics of lateral migration in small voids and how this impacts the resulting LMR image contrasts; the procurement of samples of materials of industrial importance with flaws and defects; the application of LMR to the detection of flaws and defects in these samples; the development of a multi-detector scanning system to provide for faster, more effective flaw detection; and a determination, for the types of samples examined, of the limits and capabilities of flaw detection using LMR.LMR imaging measurements on the machined samples showed that the optimum contrast in flaw-to-background signal intensity occurred at an X-ray energy of 75 kVp for the aluminum samples and at 35 kVp for the Delrin sample. Monte Carlo simulations and experimental measurements on the aluminum samples showed that LMR is capable of detecting defects down to the tens of microns range. Measurements on the aluminum samples also showed that LMR is capable of detecting relatively small composition variations; a 30 % difference in image intensity was observed for aluminum samples that had a few percent difference in trace iron and copper content.LMR scans on aircraft samples showed that LMR is very good at detecting corrosion. Intensity decreases of up to 25 to 30 % were observed in corroded areas relative to the intensities in clean areas. Especially significant were scans of samples performed with the clean or uncorroded side facing up. The corrosion on the opposite side of these {approx} 2 mm thick samples, where there was contact between the frame member and the aircraft skin, was clearly visible. This demonstrates that LMR is capable of picking up composition changes on the inside of shell-like components with only outside surface area access. Scans of other samples showed that LMR is capable of detecting small flaws on the inside of shell-like components with only outside surface area access. Cracks around a fastener hole that were {approx} 15 mm in length and no more than 0.25 mm in width were seen through the aircraft skin. Scans of aluminum honeycomb structure demonstrated that LMR is also capable of picking up internal defects that include regions of crushed core and areas of debonding.