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Evaluation of Pd-Cr Wires for Strain Gage ApplicationA newly developed alloy, palladium-13 weight percent chromium (Pd13Cr), was identified by United Technologies Research Center under a NASA contract to be the best material for high temperature strain gage applications. An electrical resistance strain gage that can provide accurate static strain measurement to a temperature higher than that of a commercially available gage is urgently needed in aerospace and aeronautics research. A strain gage made of a 25.4 micron (1 mil) diameter Pd13Cr wire has been recently demonstrated to be usable for static strain measurements to 800 C. This compares to the 400 C temperature limit of the commercially available strain gages. The performance of the Pd-Cr gage, however, strongly depends on the quality of the Pd13Cr wire. Four batches of Pd-Cr wires purchased from three different manufacturers were therefore evaluated to determine the best source of the wire for strain gage applications. The three suppliers were Precious Metal Institute in China, Sigmund Cohn Co., and G & S Titanium, Inc. in the United States. Two batches of wires obtained from Previous Metal Institute in 1987 and 1992, respectively are referred to herein as China87 and China92 wires. The mechanical, chemical and electrical properties of these wires, both as-received and after high temperature exposures at 800 C for 50 hours were analyzed. The elastic modulus and the failure strength of the wires were evaluated using a tensile test machine equipped with a laser speckle strain measurement system. The chemical and microstructural properties of the wires were inspected using a plasma atomic emission spectrometer and a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscope (EDS). The electrical stability and repeatability of the wires were determined by measuring the electrical resistance of the wires during three thermal cycles to 1000 C and a ten-hour soak at 1000 C. As a result of this study, the wire which has the highest strength, the least impurities content, the best oxidation resistance and the best electrical stability will be selected for upcoming strain gage applications.
Document ID
19950014842
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Lei, Jih-Fen (NYMA, Inc. Brook Park, OH., United States)
Greer, L. C., III (NASA Lewis Research Center Cleveland, OH, United States)
Oberle, L. G. (NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 6, 2013
Publication Date
February 1, 1995
Subject Category
Instrumentation And Photography
Report/Patent Number
NASA-TM-106857
NAS 1.15:106857
E-9448
Accession Number
95N21259
Funding Number(s)
CONTRACT_GRANT: NAS3-27186
PROJECT: RTOP 505-62-50
Distribution Limits
Public
Copyright
Public Use Permitted.

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