Costly low pressure bearing support cracking problem resolved through additive damping

Abstract

The component is the low pressure bearing support (LPBS) of the TF‐41 jet engine. The LPBS was experiencing high cycle fatigue failures in the four vanes used to supply and scavage oil for the front bearing. High cycle fatigue failure in this vane case assembly is a general problem in currently operating turbine engines. A program was conducted to design and engine test a constrained layer damping wrap to control the problem. This project was conducted as a cost savings alternative to the current high maintenance effort to repair the high cycle fatigue cracks, and the redesign of the component and implementation of the new component in the fleet. The requirement for the damping treatment was to significantly reduce the dynamic response (and thus reduce the dynamic stresses) of the oil carrying vanes in their operating temperature range; and, the thickness of the application was to be not greater than 0.016 in., so as not to affect engine performance. The laboratory test showed a factor of ten decrease in dynamic response due to the application of the damper wrap, while the engine test cell run showed a dynamic stress reduction of eighty to ninety percent. This paper will describe the utilization of modal analysis data for damping treatment planning, the process for damping treatment design optimization, and proof testing on an operational engine. [This work was supported by the United States Air Force Materials Laboratory.]