Abstract
A prototype of an embedded optical sensor mainly made of a quartz fiber and a Si photodiode is developed to measure recession behavior of an ablative heatshield material. In order to test the operational principle of the developed sensor, a composite test specimen is prepared: a spread carbon fiber sheet is put onto a graphite tube. The spread carbon fiber sheet is ablated by irradiating the frontal surface of the sheet by using a CO_2 laser, and the radiation emanated from the back surface of the heated sheet is detected by using the fabricated optical sensor embedded into the graphite tube. The irradiated surface is recorded by using a video camera. In the present study, the ablative characteristics of the spread carbon fiber sheet are interpreted by comparing the recorded images with the temporal variation of the sensor output voltage. The results implies that the developed sensor works in principle: the sensor can successfully detect the rapid increase of the temperature of the sheet, and the mass loss behavior of the ablated spread carbon fiber sheet.
