<title>Creep measurement of refractory material in high-temperature tensile loading tests</title>

Abstract

In the design of aerospace materials, developmental testing is conducted to characterize the behavior of the material under severe environmental conditions of high stress, temperature and vibration. Such materials are designed to withstand these environmental extremities without undergoing mechanical failure. Of importance is the performance of the materials at elevated temperatures, particularly the yield strength, which must be known so that the component can be designed to operate below such limits. Currently, instrumentation used in high-temperature tests must rely on long throw instrumentation, such as a knife-edged extensometer, to probe the surface of the specimen. This often results in reduced accuracy and limits the flexibility available for material evaluation. In this paper, we present the development of a fiber optic strain gage which was used for creep measurement of a stainless steel specimen (Type 304) heated to a temperature of 1400 degree(s)F (760 degree(s)C) during tensile loading tests. Surface attached fiber optic strain gages designed for a .3% dynamic range were completely immersed in a 1400 degree(s)F (760 degree(s)C) furnace throughout the duration of the test. The yield strength of the steel specimen evaluated with optical strain sensors agreed well with the manufacturing specifications. In addition, strain measured with the optical fiber strain sensor showed a difference of less than 0.01% compared to a ceramic knife-edged extensometer.