Sylvie Aubry (saubry@sandia.gov) *Reese E. Jones (jones@sandia.gov) 3Jonathan A. Zimmerman (jzimmer@sandia.gov) This page intentionally left blank. 4 Abstract Sandia National Laboratories are interested in obtaining a thorough understanding of how aging processes affect the reliability and performance of weapon components. Microscale parts that are manufactured using the LIGA process are being considered as replacements in the refurbished weapons and life extension programs. Dormancy issues are

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... particularly relevant to these parts. In this report, a method to study the dormancy phase and adhesion force of two nickel LIGA micro-gears in contact is presented. It is based on an analysis of the preferred states of the system, which correspond to local energy minima. The system is inactive for a long period of time and the assumption is made that, from a microscopic point of view, it reaches an equilibrium state that corresponds to a local, if not global, energy minimum. Energy minima do not correspond exactly to states of equilibrium in the system but are important states since they have higher probabilities to be present after dormancy than other states. The configuration with the highest probability corresponds to the global energy minimum. This report considers a system composed of two micro-gears in contact for a long period of time in a special storage environment. The questions arising in this problem are: first what will the interface of the two micro-gears look like after the dormancy period, and, second what will be the force necessary to pull both micro-gears apart or equivalently what is the adhesion force at the interface of the surface of the gears? In this particular system, details of the microstructure are of the order of the nanometer and so are sufficiently small to be analyzed at the atomic scale. Thus, particle simulation techniques are explored to analyze the evolution of these details with time. The system which is studied in this report is a mathematical simplification of the real system. The goal is to understand how the shape of the asperity influences its behavior. The asperities were placed in contact in various combinations and a study of how the shape and the offset of two asperities in contact influence their behavior is done in this report. The dormancy phase is modeled by looking at energy minima of the system and is implemented using molecular static simulations. Also the adhesion force is estimated using molecular dynamics and the evolution of the force necessary to pull the two asperities in contact apart is evaluated for different possible shapes and dimensions.