Aerospace Non-Destructive Evaluation

Digiray® real-time Reverse Geometry X-ray^® (RGX^®) systems open up new opportunities in aerospace non-destructive evaluation (NDE):

• unparalleled contrast resolution (up to ten times better than conventional systems)
• increased throughput (no film to develop)
• completely digital (first-generation image quality)
• small detectors (one centimeter square)
• detects corrosion, impact damage, cracks, foreign objects, and flaws in manufacturing that conventional x-ray systems cannot resolve.

Typical aerospace applications include NDE of

• corrosion
• impact damage
• water entrapment in both aluminum and
• composite structures

Advanced features include post-acquisition digital image enhancement, 3-D imaging and Motionless CT™ (laminography), a cost-effective alternative to computerized tomography (CT) that is capable of viewing samples one layer at a time.

RGX® technology is production-proven for composite parts on the F-117. 
NASA has been using RGX® since 1993. 
Digiray® also performs sample analyses at its headquarters in San Ramon, California.

Diverse applications include

• turbine engine blades
• helicopter blades
• quality assurance for manufacture and repair

Current developments:

• Ruggedization of portable systems with miniature detectors for testing aircraft and pipes without dismantling them.
• Further advancement of Motionless CT™ (laminography) hardware and protocols.

Corrosion and Cracks

	The unparalleled contrast sensitivity of Digiray® Reverse Geometry X-ray® systems make them ideal for corrosion and crack detection. Figure 1 shows corrosion on the "tip cap" of a horizontal stabilizer of the U.S. Air Force's F-111 Aardvark fighter/bomber.
	Two Delta Airlines skin layers depicting a stress corrosion induced crack (on the left) and sealant voiding. The crack is concealed under a layer of .16 inch skin.
	Crack in a U.S. Air Force F-111 strake composite piece made of 3-ply Kevlar and 4-ply Graphite/Epoxy.

(These and all images on this web site copyright Digiray Corporation.)

Metal Matrix Composites

	Titanium metal matrix (pseudocolor) with warped fibers
	Composite coupon consisting of eight plies of silicon fibers embedded in a titanium matrix. Both the 0.0065 inch (0.0165 cm) horizontal fibers and the even finer vertical reinforcements are visible.

Impact Damage and Curing

	Impact damage on carbon fiber epoxy used in Air Force research for advanced composites.  An RGX® system, mounted on a robotic gantry, has imaged blades for the NASA tilt-rotor type aircraft, the XV-15.
	NASA Ames composite wind tunnel blade showing both impact damage and defects caused by swirling in the microballoon epoxy during curing.

Composite Honeycomb and Water Entrapment

Composite honeycomb (Nomex core with Kevlar skin) with excess resin or water entrapment. The system also excels at detecting crushed core.

RGX® sensitivity to moisture in honeycomb is comparable to that of neutron radiography.

Diverse Applications

NASA has commissioned RGX® tests on Space Shuttle tiles to determine bonding quality.

Digiray® has also performed analyses for the following NDE applications:

• residual core in turbine blades

• fuzes for explosive charge detonation

• air bag initiators for the automotive industry

Engine Parts

Crack in an 11 cm x 12 cm aircraft engine stator blade (vertical yellow line near center of image).

Pressure sensor

Internal Integrity

Cross section of a NASA XV-15 Tilt Rotor Blade with a spar-wall separation defect.

The RGX® system can find hidden defects ranging from loose connections on electrical heating elements within helicopter blades to foreign bodies embedded into composites. NASA, the United States Army, and the United States Air Force have used RGX® technology to image helicopter blades.

Repair of Advanced Composites

Repair patch on a .5 inch (1.27 cm) low visibility ("stealth") quartz polymide fiber coupon from an aircraft radome. Also visible are details of the composite weave and subtle changes in object thickness and bonding material.

Advanced Features

RGX® systems offer an array of techniques for enhancing images and for displaying them, such as field flattening, slice and density plots, edge enhancements, histogram and gray scale or pseudo-color remapping.

	The RGX® system features many image-processing enhancements that can aid in x-ray image analysis. The 3-D Density Plot maps density as height, so material loss due to corrosion appears as a hole. The wells were milled into an aluminum sample (1% and 2% of the original thickness) and masked with corrosion powder.
	McDonnell-Douglas DC-8's fuselage skin repair. (With a 'Tint-Rolling' feature, you can change the gray-value distribution to amplify small density variations and display them either in gray or false color. If you download the self-extracting demonstration program file RGXAERO.EXE from the download demos page, you will able to 'tint-roll' through all the images shown on this page plus many more.

Current Development Work

NASA Langley Research Center, Hampton, Virginia has purchased RGX® systems for

• portable detection of corrosion in aging aircraft/spacecraft

• development of new, advanced materials and structures

RGX® imaging is also suited for research into the failure modes of metal matrix composites at high stress levels.

Digiray® is improving the technology in such areas as precise three-dimensional measurement and detector miniaturization. Current detector size ranges from 0.1 inch (3 mm) to 1 inch (30 mm). In situ placement of miniature detectors (Mini-Probes) enables single-wall transmissive inspection for

• robotic welding (probe inside tube)

• aircraft engine afterburner cans

• simplified on-wing corrosion detection (probe inside fuel tank)

	Transmissing x-ray through both walls of a corroded pipe does reveal a defect, however . . .
	Placing a Mini-Probe inside the pipe reveals greater detail.

PORTABLE INSPECTION

Another option, unique to Reverse Geometry X-ray®, increases inspection throughput. An array of relatively inexpensive detectors can be placed throughout the fuselage or wing structure, each one, in turn, picking up x rays from the source as it passes by. Miniature detectors could even be manufactured into aircraft structures for routine monitoring of corrosion.

With the addition of pattern recognition software and standard handling mechanisms, the system is amenable to automated on-line factory inspection.

State-of-the-Art

With the successful implementation of many applications, including Motionless CT™ (laminography--a form of computed tomography), miniaturization and portability, Digiray has proven the unique value of Reverse Geometry X-ray® imaging. Digiray® has gone beyond conventional x-ray NDE to spawn an array of new tools for NDE radiography in manufacturing and research.

For more information: contact Digiray (925) 838-1510; info@digiray.com
http://www.digiray.com
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