High-Temperature Strain Sensing

High-Temperature Strain Sensing

An Armstrong research team is advancing a fiber optic sensor that can measure strain on structures exposed to temperatures approaching 1,800 o F, such as reentry vehicles. An initial goal is to provide strain data in support of finite element model validation and thermal-structural analyses as part of testing in NASA's Flight Loads Laboratory. That research effort is developing sensor attachment techniques for structural materials at the small test-specimen level and then applying those methods to large-scale hot-structure test articles.

Work to date: The team has performed laboratory tests on control surfaces from the X-37 reentry vehicle, characterized the sensor, and generated corrections to apply to indicated strains. Substrates

ranging from metallic super alloys, carbon-carbon, and ceramic matrix composites have been tested under combined thermal-mechanical loads in both air and inert nitrogen atmospheres.

Looking ahead: The team will examine the use of sapphire-based, rather than silica-based, fiber optic interferometry to further increase the temperature range towards 3,000 o F. Additional work includes ruggedizing the sensor and developing installation methods that would lessen the expertise required to attach these sensors.

Benefits

 High-temperature sensing: Enables strain measurements at much higher temperatures than current methods

 Unbiased: Does not add localized stiffness

Applications

      Reentry vehicles  Jet engines

      Nuclear facilities

      Control surfaces during hypersonic flight

Fiber Optic Sensing

Armstrong's portfolio of Fiber Optic Sensing System (FOSS) technologies offers unparalleled options for high-resolution sensing in applications that require a unique combination of high-powered processing and lightweight, flexible, and robust sensors. The system measures real-time strain, which can be used to determine two-dimensional and three-dimensional shape, temperature, liquid level, pressure, and loads, alone or in combination. Initially developed to monitor aircraft structures in flight, the system's capabilities open up myriad new applications for fiber optics-not just in aerospace but also for civil structures, transportation, oil and gas, medical, and many more industries.

The Armstrong approach employs fiber Bragg grating (FBG) sensors, optical frequency domain reflectometry (OFDR) sensing, and ultra-efficient algo-rithms (100 samples/second). Engineers are continually seeking new ways of looking at information and determining what is important. Armstrong's FOSS technologies focus on critical research needs. Whether it is used to determine shape, stress, temperature, pressure, strength, operational load, or liquid level, this technology offers ultra-fast, reliable measurements.