W. Zhuang, B. Wicks, Defence Science and Technology Organisation, Melbourne, Australia

Summary:

Mechanical surface enhancement methods, such as shot peening and low plasticity burnishing have been demonstrated to improve high cycle fatigue strength for application to gas turbine engine blades. An additional benefit is that, compared with a traditional shot peening surface treatment, low plasticity burnishing can dramatically improve the tolerance of blades to foreign object damage. These property improvements are attributable to deep, high magnitude compressive residual stresses induced by the low plasticity burnishing process. In addition to engine blades, engine disks are also fatigue-critical and high-cost components in gas turbine engines. The present study investigates the effect of low plasticity burnishing on low cycle fatigue lives of engine disks.

In this paper, an engine disk-bore specimen was designed to represent a specific engine disk feature. Shot peening was used to treat the surfaces of one group of the disc-bore specimens, and low plasticity burnishing was used to treat the surfaces of the other group. After each surface treatment the specimens were subjected to low cycle fatigue loading. The low cycle fatigue tests were carried out in four-point bending at a cyclic frequency of 0.5 Hz. After varying numbers of load cycles, residual stresses at the surface of the specimens were measured using an X-ray diffraction system. These measurements, representing different stages in the low cycle fatigue life, were used to monitor residual stress relaxation. This paper reports the effect of both surface treatments on low cycle fatigue and an evaluation of the effects in terms of the residual stress relaxation under low cycle fatigue loading.