PSI - Issue 14

S. Narendar et al. / Procedia Structural Integrity 14 (2019) 89–95 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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deflection at the failure is 4.3 times of the initial deflection. But the resultant lateral load at failure is 2.5 times of the proof value. It is clear that the ceramic radome deformation is higher due the presence of the thermal load. The thermally degraded joint is lead to more deformation on the radome. Here lateral load versus deflection slope is very rapid due to the weakening of the ceramic and metal joint. The desired and achieved temperature profiles are shown in Fig. 4(a). A close match between the desired and achieved profiles can be seen; this is achieved based on the fine-tuned PID gains as per the requirement of the heat load to the ceramic radome. The cumulative heat fluence is calculated based on the test results and plotted in Fig. 4(b). The maximum fluence estimated is around 95 kJ/m2. Peak electric IR power used in the test is 118kW (see Fig. 4(c)) and the measured front wall and back wall temperatures are plotted in Fig. 4(d). The back-wall temperatures are only at 10% of the front wall temperature. The present thermo-structural loads as per the predictions from a critical trajectory case of the missile. The critical trajectory is an envelope of all the angle of attacks of the missile. As the angle of attack increases the combined loads play a critical influence on the complete airframe of the missile and especially more on the nose part, i.e., ceramic radome. As angle of increases, the projected area of the radome with respect to the incoming flow also increases and leads to more pressure load and also the thermal load. All these effects are considered while finalizing the thermal and structural loads for radome qualification. The radome withstood both the thermo-structural loads and the joint of the radome and bulkhead was qualified for the design loads and the structural integrity of the radome assembly is proven up to failure loads. The handling of the ceramic radome while applying structural load is a very careful thing and design of the Teflon simulators at as per the external profile of the radome is carried out to cater the need of structural loading. The control thermocouple on the front wall of ceramic radome needed multiple iterations for finalizing the PID gains to tune the very short duration (~15 sec) temperature profile. High emissivity black paint is applied on the radome, since the radome is white in colour, to reduce the power input limits to the heaters and to make the radome close to black body. With all these factors, the ceramic radome and its joint with metallic bulkhead is tested for thermo-structural loads successfully. The structural integrity of a ceramic radome and its joint with the metallic bulkhead was proven under the combined application of the thermal and structural loads. The subsystems involved in carrying the thermo-structural evaluation of radome are discussed in detail along with the experimental results. References FD Groutage, Radome development for a broadband rf missile sensor, 1977, NASA TR 2023. K. Kishore Kumar, T. Nagaveni, C. S. Prakash Rao, Development of Silicon Nitride-Based Ceramic Radomes — A Review, Int. J. Appl. Ceram. Technol., 1 – 12 (2014). A. H. Julian, A. J . Eggers Jr. Corp. “A study of the motion and aerodynamic heating of missiles entering the earth's atmosphere at high supersonic speeds”, NACA -RM-A53D28, 1953. G. I. Maykapar. “Aerodynamic heating of the lifting bodies”, NASA -CR-97576, ST-AD-HT-10770, 1968. R. Wesley Truitt. “Fundamentals of aerodynamic heating”. The Ronald Press, New York, 1960. H. J. Thomas, R. W. Lance, G. Leslie. “A technique for transient thermal testing of thick structure”, NASA -TM-4803, 1977. 6. Conclusions