Design Modification to Enhance Fatigue Life of an Aero-Engine Heat Shield

An aero-engine heat shield made up of corrosion resistance steel sheet and mounted between the nozzle box and the exhaust unit of a gas turbine engine was frequently getting rejected due to crack initiation at the periphery of the apertures. Also higher amplitude of vibration was observed in heat shield during operation of the engine. A detailed structural and vibration analysis of the heat shield was carried out to find out the reasons for this pre-matured failure. Based on the results of the analysis, the heat shield was modified, by introducing flat stiffeners, welded around the apertures to evade crack initiation. This modification increased fatigue life and reduced vibration level of the heat shield. The heat shield is successfully subjected to airworthiness qualification test in the aero-engine test bed and subsequently type certified for use in engine.