Quantitative Nondestructive Evaluation of Carbon-Carbon Composites by Pulsed Infrared Thermography

Among all the nondestructive evaluation (NDE) techniques that are used in industry, Stimulated Infrared Thermography (SIRT) is very attractive because of its noncontact and rapid-scanning ability [1]. In our laboratory, we applied this technique to composite materials which are often used in aerospace structures. In particular, we applied it to carbon/epoxy composites [2,3]. Due to the relatively low refresh frequency of the monocell IR cameras, the application of the method was restricted to low thermal conductors. Some new developments of the data reduction procedure were presented last year [4] to use this technique with good heat conductors. Satisfactory results were obtained in the case of delaminations in carbon/carbon (c/c) composites which will constitute the hottest parts of the thermal protection of the european space shuttle Hermes. A few months ago, we presented an improvement of this data reduction procedure which is able now to work with any kind of material and we applied it on the especially difficult case of the characterization of adhesive joints in metallic structures [5]. We present here the last results obtained in c/c composites by our SIRT techniques with the new data reduction procedure.</p

Experimental Study of Ignition over Impact-Driven Supersonic Liquid Fuel Jet

This study experimentally investigates the mechanism of the ignition of the supersonic liquid fuel jet by the visualization. N-Hexadecane having the cetane number of 100 was used as a liquid for the jet in order to enhance the ignition potential of the liquid fuel jet. Moreover, the heat column and the high intensity CO2 laser were applied to initiate the ignition. The ignition over the liquid fuel jet was visualized by a high-speed digital video camera with a shadowgraph system. From the shadowgraph images, the autoignition or ignition of the supersonic liquid fuel jet, at the velocity of 1,186 m/s which is a Mach number relative to the air of 3.41, did not take place. The ignition still did not occur, even though the heat column or the high intensity CO2 laser was alone applied. The attempt to initiate the ignition over the liquid fuel jet was achieved by applying both the heat column and the high intensity CO2 laser. Observing the signs of luminous spots or flames in the shadowgraph would readily indicate the presence of ignitions. The mechanism of the ignition and combustion over the liquid fuel jet was clearly clarified. Moreover, it was found that the ignition over the supersonic liquid fuel jet in this study was rather the force ignition than being the auto-ignition induced by shock wave heating