SUMMARY

Fretting can be considered as a small amplitude cyclic relative motion. Nuclear reactors are designed to operate at high temperatures as it results in substantial improvements of thermal efficiency. The structural and in-core components of a high/very high temperature gas cooled reactors (HTGR/VHTRs) are exposed to this high temperature environment. In components such as valve stems and seats, control rod drive mechanisms, fuel handling mechanisms, and helium circulators, fretting wear and fretting fatigue can significantly reduce the operational lifetime of these components. Inconel 617 and Incoloy 800H are nickel-based alloys, commonly used materials in HTGR/VHTRs. These alloys possess excellent high temperature corrosion, strength, and oxidation resistance properties. The fretting contact behaviors between these two alloys in room and high temperatures are investigated to obtain fundamental knowledge of fretting wear and fretting fatigue mechanisms. The purpose of this work is to understand the physical phenomena of the fretting system. It is desirable to model a numerical model for the fretting system and do the stress strain analysis at and under the contacting interface, which helped understand the mechanisms of fretting wear and fretting fatigue. It is also desirable to develop analytical and semi-analytical solutions for fretting wear volume, which helped understand the relation between wear volume, normal load, amplitude, and material properties during the fretting motion. The understanding of the physical phenomena of fretting, in turn, may lead to mitigation methods which alleviate the fretting damage. Thus, the objective of this research is to model the fretting system, identify its physical phenomena, and propose mitigation methods to reduce the fretting damage.