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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adverse environments while having an insignificant effect on the electrical performance of the enclosed antenna or antennas. The material used in building the radome allows a relatively un-attenuated electromagnetic signal between the antenna inside the radome and outside equipment (see Groutage (1977)). Today, radomes find wide applications in ground, maritime, terrestrial (ground), vehicular, aircraft, and missile electronic systems. Aerodynamic considerations play a major role in radome design, especially in the areas of shape and material. Shape sets aerodynamic drag whereas materials determine response to aerodynamic heating, dynamic pressure, and rain erosion as mentioned by Kishore Kumar et. al. (2014).

Nomenclature DACS Data Acquisition and Control System IR Infra-red PID

Proportional, Integral and Derivative Control

When a vehicle flies through atmosphere at high speeds, the thickness of the boundary layer decreases and consequently this leads to an increase in the velocity gradient in the boundary layer at the wall and hence a rise in the viscous friction. Because of this steep velocity gradient, the kinetic energy of the fluid stream is dissipated to an increase in internal energy of the fluid at the wall & hence an increase in temperature, see Julian and Eggers (1953). This phenomenon is called aerodynamic or kinetic heating . This aerodynamic heating may constitute a major problem in the design of a high-speed missile. Hence, during the preliminary design phase of the missile project, it is important to estimate the heat transfer rate and temperature on the critical portions of the missile. Aerodynamic heating results from the airflow about the surface of the missile, friction of the air along the surface of the missile and compression at and near the stagnation region of the missile external components. The heating depends on vehicle trajectory (time versus altitude and Mach number), vehicle geometry and properties of structural material (Maykapar (1968)). This manuscript describes the closed-loop temperature control technique that was developed for thermal testing of missile airframe structures. A brief discussion of traditional feedback temperature control, as applied to transient thermal testing, and representative data are also presented. Experimental results obtained using the closed-loop temperature control method are discussed in detail with experimental evidence. The objectives of the tests are mainly to qualify the radome by achieving the predefined transient temperature profile during the test and also to evaluate the structural integrity of the radome subjected to combined thermal and structural loads. Aerospace vehicles like Missiles, spacecraft, rockets, etc., which fly at high Mach numbers, experience aerodynamic heating. Because of the kinetic heating, the airframe gets heated up to varying levels over the length of the missile. The temperatures at a location on the missile airframe during the course of its flight, depends on the local flow conditions. At elevated temperatures, the materials used in aerospace structures, show a decreasing trend in their strength. The airframe of the missile systems, are designed such that they do not fail because of the reduction of strength at elevated temperatures. It is important that a flight worthy airframe does not lose its integrity during the flight due to elevated temperatures. Also, the airframe houses a number of electronic systems and subsystems essential for the working of the missile system. As per Truitt (1960) these electronic systems can operate within a limited range of ambient temperatures and need to be protected from high temperatures using thermal coatings and protection systems. To ascertain the structural integrity of the airframe of missile systems at both room temperature and at elevated temperatures, before they are flight tested, a number of thermal and thermo-structural tests need to be done on them, through ground testing (ref. Thomas et. al. (1977)). As the present test is to qualify the manufacturing process of a ceramic radome under combined thermal and 2. Need of Ground Testing