NASA Scientific and Technical Aerospace Reports

20040111963 NASA Langley Research Center, Hampton, VA, USA
Classification of Magneto-Optic Images using Neural Networks
Nath, Shridhar; Wincheski, Buzz; Fulton, Jim; Namkung, Min; [1994]; 3 pp.; In English; No Copyright; Avail: CASI; A01,
Hardcopy
A real time imaging system with a neural network classifier has been incorporated on a Macintosh computer in
conjunction with an MOI system. This system images rivets on aircraft aluminium structures using eddy currents and magnetic
imaging. Moment invariant functions from the image of a rivet is used to train a multilayer perceptron neural network to
classify the rivets as good or bad (rivets with cracks).
Author
Image Classification; Imaging Techniques; Magneto-Optics; Neural Nets; Aircraft Structures
20040120900 ATK-Thiokol Propulsion, Brigham City, UT, USA
Identifying, Assessing, and Mitigating Risk of Single-Point Inspections on the Space Shuttle Reusable Solid Rocket
Motor
Greenhalgh, Phillip O.; [2004]; 7 pp.; In English; 22nd International System Safety Conference, 2-6 Aug. 2004, Providence,
RI, USA; Original contains color illustrations
Contract(s)/Grant(s): NAS8-97238; Copyright; Avail: CASI; A02, Hardcopy
In the production of each Space Shuttle Reusable Solid Rocket Motor (RSRM), over 100,000 inspections are performed.
ATK Thiokol Inc. reviewed these inspections to ensure a robust inspection system is maintained. The principal effort within
this endeavor was the systematic identification and evaluation of inspections considered to be single-point. Single-point
inspections are those accomplished on components, materials, and tooling by only one person, involving no other check. The
purpose was to more accurately characterize risk and ultimately address and/or mitigate risk associated with single-point
inspections. After the initial review of all inspections and identification/assessment of single-point inspections, review teams
applied risk prioritization methodology similar to that used in a Process Failure Modes Effects Analysis to derive a Risk
Prioritization Number for each single-point inspection. After the prioritization of risk, all single-point inspection points
determined to have significant risk were provided either with risk-mitigating actions or rationale for acceptance. This effort
gave confidence to the RSRM program that the correct inspections are being accomplished, that there is appropriate
justification for those that remain as single-point inspections, and that risk mitigation was applied to further reduce risk of
higher risk single-point inspections. This paper examines the process, results, and lessons learned in identifying, assessing, and
mitigating risk associated with single-point inspections accomplished in the production of the Space Shuttle RSRM.
Author
Identifying; Inspection; Reusable Rocket Engines; Space Shuttle Boosters; Risk
20040120973 NASA Langley Research Center, Hampton, VA, USA
Issues on Reproducibility/Reliability of Magnetic NDE Methods
Namkung, M.; Fulton, J. P.; Wincheski, B.; Nath, S.; [1994]; 8 pp.; In English; No Copyright; Avail: CASI; A02, Hardcopy
One of the critical elements related to the practicality of any NDE technique is its reproducibility under nominally the
same inspection conditions. The results of certain test methodologies, however, are not always repeatable and understanding
the origin of the irreproducibility is often as critical as obtaining reproducible results. One example is the characterization of
residual stress in structural ferromagnets using the magnetoacoustic (MAC) method. Although it has not been widely
publicized, the test results of this method are known to be time-dependent. Two distinct types of time dependencies have been
observed during testing. The first type has a clearly definable relaxation time, while no such trend has been observed for the
second. The purpose of the present study is to systematically investigate the time dependence of the second type, to find out
the range and, if possible, the origin of the variation in the test results. For this, MAC curves were obtained under various stress
levels and the tests were repeated over time. Particular attention was given to whether noise in the measuring device or a
change in the laboratory environment could have been a contributing factor. The steel samples used for the study were cut from
C- and U-class railroad wheels. The MAC behavior of these samples was reported previously. Each steel sample was first
machined to be a cylindrical rod of 3.175 cm (1.25 in) in diameter and 26.67 cm (10.5 in) in length. The center portion of
the samples were further machined to form a pair of flat and parallel surfaces for the launch and reflection of the ultrasonic
pulses. Data acquisition involved two major elements; magnetic and acoustic measurements. Throughout the experiment the
net magnetic induction, B, was measured by integrating the induction pickup coil output using an integrating fluxmeter. The
acoustic measurements employed the phase-locked technique which will be described in the following.
Derived from text
Nondestructive Tests; Magnetic Measurement; Magnetoacoustics; Stress Measurement
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