Detection of defects in foam thermal insulation using lateral migration backscatter x-ray radiography

Abstract

A new Compton x-ray backscatter imaging technique called lateral migration radiography (LMR) has been successfully applied to the detection of voids and delaminations in the foam thermal insulation used on the shuttle external tank. LMR employs detection of selected scatter field velocity components, by using specially designed detectors and detector collimators, to achieve high image contrast.LMR is based on image contrast generated by migration of probe x-ray radiation in directions transverse to the illumination radiation beam. Because LMR is sensitive to electron density variations in these directions, thin, but large density variations, such as cracks and delaminations, generate signal-to-background ratios sufficient to produce images of features which are not even detectable in the usually interrogated thin dimension.The examined foam thermal insulation test panels consist of aluminum plates onto which the sprayed-on foam insulation (SOFI) is applied. Some of the test panels include structural features bolted to the base plate. The SOFI was layed down over the base plate and structure with a thickness varying from a few tens of mm up to a few hundred mm. The test panels included voids and simulated delaminations in the SOFI ranging in cross-sectional size from 6 x 6 mm to 50 x 50 mm. High quality images were acquired using pixels of 2 to 3 mm and irradiation times of as low as 0.05 s per pixel.

Nondestructive Evaluation (NDE) for Characterizing Oxidation Damage in Cracked Reinforced Carbon–Carbon

“…X‐ray CT was used to size oxidation damage and cracking, and develop three‐dimensional volumetric visualizations. Dugan and colleagues 4–8 provide basic principles for the various methods, and experimental parameters for the methods are given here. Specialized image processing was used as needed to highlight indications from the NDE methods using software developed at NASA and available in the public domain 9 .…”

“…www.ceramics.org/ACT NDE for Characterizing Oxidation Damage BSX: A scanning BSX system was used to image the RCC samples. 4 Several parameter settings were used to determine optimized conditions but for the purposes of comparing pre-and postoxidation images, the following settings were used in those cases. The settings were aperture of 2 mm, voltage of 55 kV, current of 11.6 mA, focal spot size of 1 mm, finned collimator angle of 901 and exposure time per scan position of 0.2 s. The scan parameters included scan (X) and step (Y) increments of 0.5 mm and scan velocity of 2.5 mm/s.…”

“…BSX: A scanning BSX system was used to image the RCC samples 4 . Several parameter settings were used to determine optimized conditions but for the purposes of comparing pre‐ and postoxidation images, the following settings were used in those cases.…”

NDE for Characterizing Oxidation Damage in Reinforced Carbon‐Carbon

“…5 Several parameter settings were employed to determine optimized conditions but for the purposes of comparing prior and post-oxidation images, the following settings were used in those cases. The settings were aperture of 2 mm, voltage of 55 kV, current of 11.6 mA, focal spot size of 1 mm, finned collimator angle of 90° and exposure time per scan position of 0.2 sec.…”

NDE of spacecraft materials using 3D Compton backscatter x-ray imaging

“…A critical aspect of this study is on methods that could potentially be applied on-orbit or on mission. Previous to this work other 3D back-scatter systems have been attempted with mixed results [1] although several 2D backscatter systems have been developed and used on several thermal protection systems [2].…”