In recent years, there have been a number of failures of aircraft engine and structural components which are believed to have resulted from the accumulation of fatigue damage. The treatment of such damage is therefore of great significance from the standpoints of increased reliability and extended usage.

This paper presents the initial results of a program to evaluate a new process for the repair of fatigue-damaged aircraft engine components. In this process, the fatigue-damaged area is drilled out and replaced with a bushing manufactured from a new class of material called a ‘shape memory’ alloy. This material has the capability to expand in place following insertion, thus placing the surrounding material into compression.

A significant improvement in low cycle fatigue life was observed at 288°C in Ti-6Al-4V specimens treated with the above technique. The degree of improvement is about twice that which was obtained with a mechanical cold expansion technique used commercially to extend fatigue life. The degree of improvement of the subject process is greater at high numbers of cycles than at low numbers of cycles.

The subject project was funded as a Phase I Small Business Innovation Research award administered by the U.S. Naval Air Propulsion Center. Additional work in this area is planned which will a) identify the process parameters which will optimize the properties of shape memory alloy bushings, b) define the properties of shape memory alloy bushings over a wide range of temperature and loading conditions, and c) evaluate the effect in actual turbine engine hardware in a simulated engine environment.

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