High temperature fastener fatigue

This work was commissioned in response to high temperature fatigue failures in a bolted connection that rotates at high speed. There was concern about the loss of preload in the fasteners at high temperature due to thermal expansion in the fasteners. A substitution of fastener material was made and the failures ceased. The two major focuses of this work are preload and fatigue behavior of fasteners. Preload can be determined by many different methods with varying degrees of accuracy. After investigating and testing different methods of measuring preload, a new method is proposed herein that is application specific, eliminating the need for many of the assumptions common to other methods. Modeling and testing also confirmed that the preload of original fasteners was being completely lost at elevated temperature, and the new fasteners were maintaining preload. Fatigue testing was also performed on the fasteners to determine the fatigue behavior of the fasteners and the effects of temperature on fatigue life. It was determined that maintaining preload at temperature is the most important factor on fastener life in this application, and that temperature does not have great effect over the temperature range considered.