Air Force

Uniform thermocouple molds for bonding

Tool improves data accuracy and integrity for high-temperature sensor measurements

Materials Sensors

Airman 1st Class Alexander Forest, 374th Maintenance Squadron aerospace propulsion apprentice, installs a thermocouple on part of an MC-130 Talon II at Yokota Air Base, Japan, Feb. 26, 2016.  (U.S. Air Force photo by Senior Airman David Owsianka/Released)

Air Force scientists have developed several rigid and flexible molds for bonding and encapsulating sensors using cement instead of common adhesive compounds. The patented technology is available via license agreement to companies that would make, use, or sell it commercially.

Thermocouples (TCs) are widely used as temperature sensors. Aerospace researchers are utilizing advanced modeling and simulation techniques to accurately measure the effects of typical thermo-mechanical loads present in-flight profiles. Precise dimensions must be applied to the model for the results to match the physical specimen. Unfortunately, the amount of adhesive used to affix a TC sensor to a surface can alter the dynamic response of the material being characterized. Additionally, any variability of the TC placement within the encapsulating material or irregularities in the geometry and thickness of the adhesive can impact data integrity and accuracy. Excessive adhesive shields the substrate from exposure to ambient heat sources, thus further skewing results.

There is a need for a method to encapsulate a miniaturized TC with a consistently dimensioned and positioned adhesive barrier at the desired attachment site, thus increasing analysis capabilities and extending the TC life at extreme temperatures. A team of Air Force researchers has developed exactly such a device and method for mounting high-temperature TCs while reducing installation variables that might skew data acquisition accuracy.

The new device can bond and encapsulate a sensor to a substrate by using a rigid or flexible mold made from a single piece of material or two parts joined by pins, a void, and a channel. The sensor is passed through the channel and terminated within the void at a distance from the substrate. The void is then filled with cement through an injection port to encapsulate the sensor and bond it to the substrate. The void also includes a vent port to allow air to escape.

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