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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structural loads. The main objectives of the test are:  To qualify the radome by achieving the predefined transient temperature profile during the test and  To evaluate the structural integrity of the radome subjected to combined thermal and structural loads. After the completion of thermal cycle (under proof load), the structural load is increased beyond ultimate load up to the failure of the radome. This is to check the factor of safety on ultimate load. The radome is to operate under 450 o C temperature environment and also under the maximum proof load condition of 2.5 kN axial and 4.2 kN lateral loads. The non-dimensional graphs are given in the results section. These loads are worked out after the identification of the critical trajectory of the missile. The present manuscript mainly focusses on the experimental test setup carried out for the thermo-structural qualification of ceramic radomes.

3. Test Setup and Subsystems

The complete radome thermo-structural test setup is shown in Fig. 1 and that of the linkage between the subsystems is shown in Fig. 2. One axial force (AF) and three lateral forces (LF1, LF2 and LF3) are applied through teflon formats on ceramic radome as shown in Fig. 1. In Fig. 2, the electric transformers of X = 4000 Amps capacity. The power lines from transformer to the thyristors are connected by primary and secondary MCCBs through contactor. These thyristors are triggered by gate voltage, which is decided by the PID gains, to the bus bars of IR heaters.

3.1. Preparation of the Test Article

The radome airframe section is subjected to dimensional inspection before the thermal test. Thermocouples were bonded using high temperature cement on ceramic portion and spot welding on the metallic bulkhead as per the requirement, at various locations on the test article.

3.2. Fixture and Mock Sections

A separate fixture was prepared for the thermal test on radome section and bolted to bottom side as shown in Fig. 1. The test article was placed over a fixture to make sure that they are in vertical position in front of the IR heater systems, to achieve the desired heat flux. The nearest distance between the outer surface of test article and the heater cassettes was 70 mm for desired temperature simulations. A separate Teflon based mock sections were prepared as per the external profile of the radome and placed over the radome section. These are used to load the section laterally using ropes. Similar Teflon mock section is also prepared and placed over the nose tip of radome to apply the axial load.

Fig. 1. Complete thermo-structural test setup of ceramic radome: (a) Side view and (b) top view.