FAA Fluorescent Penetrant Activities - An Update

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1 FAA Fluorescent Penetrant Activities - An Update David G. Moore Sandia National Laboratories Airworthiness Assurance ND Validation Center Albuquerque, New Mexico (505) Abstract The Federal Aviation Administration s Airworthiness Assurance ND Validation Center (AANC) is currently characterizing low cycle latigue specimens that will support the needs of penetrant manufacturers, commercial airline in dustry and the Federal Aviation Administration. The main focus of this characterization is to maintain and enhance the evaluation of penetrant inspection materials and apply resources to support the aircraft community needs. This paper discusses efforts to-date to document the Wright Laboratory penetrant evaluation process and characterize penetrant brightness readings in the initial set of sample calibration panels using Type 1 penetrant. Background Five sets of six specimens were produced with fixed crack lengths between mm and 1.27 mm. The specimens were manufactured in a manner which produces cracks having a crack length to depth aspect ratio of 2. The specimens were produced from 6.35 mm thick Ti-6A1-4V, ASTM-B- 265, Grade 5 plate stock. This material is one of the two materials used by Wright Laboratory to create the current set of qualification specimens. ts was selected for its high corrosion resistance, fracture toughness and commercial availability. The specimens were machined into blocks measuring 1.52 cm by 25.4 mm by 6.35 mm. One side of each specimen was arbitrarily chosen as the front surface to introduce the fatigue cracks. The center section of this surface was smoothed by sanding and then polished with three-micron aluminum oxide powder. The top edge along the 1.52 cm dimension was slightly rounded lo illuminate stress points that could result in undesired crack initiation during fatigue loading. A variety of defects were evaluated as stress risers to initiate crack growth. Spot welding was found to work for this application. Spot welds were easy to produce and almost always resulted in the initiation of a single crack. A Fuse-Tec Welder produced the spot weld damage. This welding method has a variable heat setting to control the amount of applied current and a variable time setting to control the current duration. Through experimentation, heat and time settings were derived that produced an area of damage about 2.54 mm in diameter. This damaged consists of an area of recast metal and a surrounding heat affected zone. With this degree of damage, fatigue cracks were found to initiate and grow to a detectable size between 20,000 to 50,000 cycles [l]. Sandia is a multiprogram laboratory operatec by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94-AL85000.

2 DSCLAMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

3 DSCLAMER Portions of this document may be illegible in electronic innage products. mages are produced fromi the best available original document.

4 Wright Laboratory Penetrant Evaluation Process For the past two years, AANC has conducted a knowledge preservation project of the present penetrant evaluation and qualification process used at Wright Laboratory in Dayton, Ohio [2]. During this time, six sample calibration panels underwent brightness evaluation testing as defined by AMS2644, Qualification of Penetrant nspection Materials. Table 1 describes the inspection steps for each inspection method using Type 1 penetrants. Table 1. Fluorescent Dye System Test Parameters SENSTVTY Penetrant Dwell Prewash Emulsification Wash Solvent Wipe Dry Developer All Methods: Dip and then drain for 5 minutes at a 60 angle Method D: Spray for 1 minute F*5) Dip arid then drain for 2 minutes Method B: lmmese for 5 minutes, no agitation Method D: (reference system: 20% concentration) (cand date system: manufacturer's recommended concentration) Spray for 1 minute Method A: Method B: Spray under blacklight until visible fluorescence is gone, for up to 2 minutes Method D: Plunge into bucket of water to stop emulsification, followed by 2 minute spray (All with 25 7OoF'*5) Method C: Wipe with a clean rag dampened with solvent. Wipe with a clean, dry rag to remove excess solvent. 5 minutes in oven Methods A, 6, & D: (125OFk5 maximum) (Follows developer when testing Forms b & c) Method C: 5 minutes at room temperature All Methods: Dip in dry powder developer (all except for candidate Forms b, c, d and e) and allow a minimum dwell of 5 minutes Each crack was centered in the eyep'iece of a PhotoResearch Spot meter. A brightness value is measured and recorded. The fatigue crack is then moved out of the field of view and a background brightness value is measured and recorded. The background value is then subtracted from the initial brightness value and entered into a database. Each test configuration is repeated several times to determine if the crack brightness readings are consistent. Penetrant Brightness Characterization The brightness data is entered into a computer database for analysis. The data is tracked in two ways. First, an aggregate of all the brightness recordings for all panels is recorded and analyzed. Second, the individual results for individual cracks is recorded and analyzed. The mean and standard deviation from the reference system database are compared to the sample calibration panels. Figure 1 displays a graph of the brightness readings for the six sample calibration samples.

5 r BAl 50.0 E A 2 BA3.A4 a 8 2 *B4 BD2 BD4 A m n f 5& 30.0 m t E E Sample Number Figure 1. Penetrant brightness readings The sample calibration panels were examined using an optical microscope and a scam electron microscope. Table 2 present!; each sample number and its measured crack length. Table 2. Crack lengths of sample calibration panels mm 1.12m.m mm 0.87mm mm 0.79mm Conclusions Each sample calibration panel displays a consistent brightness reading for different penetrant methods and sensitivities. As penetrant sensitivity increases the measured brightness readings increase. Brightness values measured from the fatigue cracks are a function of length and depth. References 1. Moore, D. G., and Larson, B. F., FAA Fluorescent Penetrant Activities, 1997 ASNT Fall Conference and Quality Testing Show, Pittsburgh, Pennsylvania, USA, October 20-24, 1997, SAND C, pp Unconfirmed Minutes, AMS Committee K Meeting, Disneyland Hotel, Anaheim, California, New Business K. 1O., March 23, 1JJ98.

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5~fi3--q7-a~C/6 CONI=- 97/093-- 4 d FAA Fluorescent Penetrant Activities David G. Moore Sandia National Laboratories Airworthiness Assurance NDI Validation Center Albuquerque, New Mexico 87185 (505) 844-7095 59.4 rfz. e 5~fi3--q7-a~C/6