Engineering topics

Lei, Jih-Fen

Publications and source records attributed to Lei, Jih-Fen.

27 records · Page 2

NASA NTRS1992

Palladium-chromium static strain gages for high temperatures

An electrical resistance strain gage that can provide accurate static strain measurement to a temperature of 1500 F or above is being developed both in fine wire and thin film forms. The gage is designed to be temperature compensated on any substrate material. It has a dual element: the gage element is a special alloy, palladium-13wt percent chromium (PdCr), and the compensator element is platinum (Pt). Earlier results of a PdCr based wire gage indicated that the apparent strain of this gage can be minimized and the repeatability of the apparent strain can be improved by prestabilizing the gage on the substrate for a long period of time. However, this kind of prestabilization is not practical in many applications and therefore the development of a wire gage which is prestabilized before installation on the substrate is desirable. This paper will present our recent progress in the development of a prestabilized wire gage which can provide meaningful strain data for the first thermal cycle. A weldable PdCr gage is also being developed for field testing where conventional flame-spraying installation can not be applied. This weldable gage is narrower than a previously reported gage, thereby allowing the gage to be more resistant to buckling under compressive loads. Some preliminary results of a prestabilized wire gage flame-sprayed directly on IN100, an engine material, and a weldable gage spot-welded on IN100 and SCS-6/(beta)21-S Titanium Matrix Composite (TMC), a National Aero-Space Plane (NASP) structure material, will be reported. Progress on the development of a weldable thin film gage will also be addressed. The measurement technique and procedures and the lead wire effect will be discussed.

Lei, Jih-Fen↗

NASA NTRS1991

The apparent strain stability and repeatability of a BCL3 resistance strain gage

Experiments were conducted at NASA-Lewis to study the effect of microstructural instability on the apparent strain stability and reproducibility of a BCL3 resistance strain gage. The resistance drift of the gage at various temperatures in the phase transition temperature range (PTTR) was measured. The effects of the heating and cooling rates with which the gage passed through the PTTR on the apparent strain characteristics of the gage were also studied. BCL3 gage, like other Fe-Cr-Al based gages, exhibited apparent strain instability in the temperature range of 700 to 1100 F due to the reversible microstructural transition the gage materials experienced in this temperature range. The BCL3 gage had a maximum apparent strain drift in the neighborhood of 770 F with an average drift rate of approx. -440 microstrain/hr in 2 hrs. The use of the BCL3 gage as well as other Fe-Cl-Al based gages for static strain measurements within the PTTR should be avoided unless the time durations in the PTTR are small enough to introduce a neglible drift. The microstructure transition that the BCL3 gage underwent occurred in the temperature range of 750 to 1050 F during heating and around 1000 to 800 F during cooling. The heating rate, and, in particular, the cooling rate with which the gage passed through the PTTR affected the shape and the repeatability of the apparent strain curve of the gage.

Lei, Jih-Fen↗

NASA NTRS1991

Palladium-chromium static strain gage for high temperature propulsion systems

The present electrical strain gage for high temperature static strain measurements is in its fine-wire and thin-film forms designed to be temperature-compensated on any substrate material. The gage element is of Pd-Cr alloy, while the compensator is of Pt. Because the thermally-induced apparent strain of this compensated wire strain gage is sufficiently small, with good reproducibility between thermal cycles to 800 C, output figures can be corrected within a reasonable margin of error.

Lei, Jih-Fen↗

NASA NTRS1990

PdCr Based High Temperature Static Strain Gage

The program at NASA Lewis Research Center to develop a high temperature static strain gage system for the hypersonic vehicle and turbine engine research has emphasized a palladium- 13wt%chromium (PdCr) alloy. Gages made from this alloy are being developed in both fine wire and thin film form. The wire gage system had platinum wire as a temperature compensator and was coated with a special alumina and zirconia mixture overcoat. This PdCr compensated wire gage responded linearly to the imposed strain to at least i000 microstrain. The strain sensitivity of the gage did not vary much with temperature. The apparent strain of this compensated gage was significantly lower than that of the other gages. It varied within 300 microstrain from room temperature to 800 deg. C with a reproducibility within 50 microstrain between thermal cycles to 800 deg. C. This is a significant advance over the 400 deg. C barrier of previous techniques for resistance static strain gages. The sputtered thin film PdCr strain gage, whose size was 8x8 mm and 10 micron thick, has demonstrated the possibility of extending the use of the PdCr strain gage to a temperature of approximately 1000 deg. C.

Lei, Jih-Fen↗

NASA NTRS1990

PdCr based high temperature static strain gage

The program at NASA Lewis Research Center to develop a high temperature static strain gage system for the hypersonic vehicle and turbine engine research has emphasized a palladium-13 wt pct chromium (PdCr) alloy. Gages made from this alloy are being developed in both fine wire and thin film form. The wire gage system had platinum wire as a temperature compensator and was coated with a special alumina and zirconia mixture overcoat. This PdCr compensated wire gage responded linearly to the imposed strain to at least 1000 microstrain. The apparent strain varied within 300 microstrain from room temperature to 800 C with a reproducibility within 50 microstrain between thermal cycles to 800 C. The sputtered thin film PdCr strain gage, whose size was 8 x 8 mm and 10 microns thick, has demonstrated the possibility of extending the use of the PdCr strain gage to a temperature of approximately 1000 C.

Lei, Jih-Fen↗

NASA NTRS1990

A resistance strain gage with repeatable and cancellable apparent strain for use to 800 C

A temperature compensated static strain gage, which is fabricated from palladium-13w/o chromium (Pd13Cr) alloy and a platinum (Pt) compensator, is being developed and was tested over a temperature range to 800 C at NASA-Lewis. The PdCr compensated strain gage has significantly lower apparent strain to 800 C than other high temperature strain gages. The PdCr compensated gage is protected from oxidation by a flame-sprayed alumina-4w/o zirconia overcoating. Test results to 800 C indicate apparent strain variations of less than 300 micro-epsilon and reproducibility between thermal cycles within 50 micro-epsilon. Apparent strain of the coated PdCr compensated gage can be predicted and cancelled due to its reproducibility and low value.

Lei, Jih-Fen↗

NASA NTRS1990

A resistance strain gage with repeatable and cancellable apparent strain for use to 1500 F

A temperature compensated static strain gauge, which is fabricated from Pd13Cr alloy and a Pt compensator, is being developed and has been tested over a temperature range to 1500 F at NASA-Lewis. The PdCr compensated strain gage has significantly lower apparent strain to 500 F than other high temperature strain gages. The PdCr compensated gage is protected from oxidation by a flame-sprayed alumina-4 wt pct zirconia overcoating. Test Results to 1500 F indicate apparent strain variations of less than 250 micro-epsilon and reproducibility between thermal cycles within 50 micro-epsilon. The apparent strain of the coated PdCr compensated gage can be predicted and cancelled due to its reproducibility and low value.

Lei, Jih-Fen↗

NASA NTRS1989

Development and characterization of PdCr temperature-compensated wire resistance strain gage

A temperature-compensated resistance static strain gage with potential to be used to 600 C was recently developed. Gages were fabricated from specially developed palladium-13 w/o chromium (Pd-13Cr) wire and platinum (Pt) compensator. When bonded to high temperature Hastelloy X, the apparent strain from room temperature to 600 C was within 400 microstrain for gages with no preheat treatment and within 3500 microstrain for gages with 16 hours prestabilization at 640 C. The apparent strain versus temperature relationship of stabilized PdCr gages were repeatable with the reproducibility within 100 microstrain during three thermal cycles to 600 C and an 11 hours soak at 600 C. The gage fabrication, construction and installation is described. Also, the coating system used for this compensated resistance strain gage is explained. The electrical properties of the strain sensing element and main characteristics of the compensated gage including apparent strain, drift and reproducibility are discussed.

Lei, Jih-Fen↗

NASA NTRS1987

Electrical Properties of Materials for Elevated Temperature Resistance Strain Gage Application

The objective was to study the electrical resistances of materials that are potentially useful as resistance strain gages at 1000 C. Transition metal carbides and nitrides, boron carbide and silicon carbide were selected for the experimental phase of this research. Due to their low temperature coefficient of resistance and good stability, TiC, ZrC, B sub 4 C and beta-SiC are suggested as good candidates for high temperature resistance strain gage applications.

Lei, Jih-Fen↗