1. Fundamental Studies of Contact Fatigue in Metallic Materials T. A. Venkatesh, Tulane University, DMR 0547903 When materials in contact such as those in hip and knee bio-medical implants or dove-tail joints in aircraft engines are subjected to dynamic loading or vibrations, localized damage originating at the contact locations could result in serious injury or catastrophic structural failure. As detection of such damage is often difficult, there is a need for better understanding the origin and progress of material damage under such localized, dynamic contact conditions. Overall, the present research work is focused on: Obtaining a fundamental understanding of the phenomenon of contact fatigue in engineering structures Formulating appropriate tools for detecting contact fatigue damage Developing materials solutions such as protective coatings for minimizing contact fatigue damage Identifying novel techniques for assessing the properties of coating materials INTELLECTUAL MERIT Motivation Objectives mm mm mm nm Methods A compressor section of the aircraft jet-engine (Courtesy – NASA, Glenn); (ii) Schematic of the dove-tail section of the turbine blade- disk assembly; (iii) Contact fatigue induced failure in a dove-tail section of a real jet-engine A Nanoindentation-based technique is being developed for estimating properties of substrates and coating materials. A sharp indenter indenting a substrate

2. The results of the current project have been presented to the scientific and technical community in the US, Europe and Asia and reported in the following archival publications. H. Lan and T. A. Venkatesh, “On the Uniqueness and Sensitivity Issues in Determining the Elastic and Plastic Properties of Power-law Hardening Materials through Sharp and Spherical Indentation”, Philosophical Magazine, 87, 4671-4729, 2007. H. Lan and T. A. Venkatesh, “On the Sensitivity Characteristics in the Determination of the Elastic and Plastic Properties of Materials through Multiple Indentation”, Journal of Materials Research, 22, 1043-1063, 2007. H. Lan and T. A. Venkatesh, “Determination of the Elastic and Plastic Properties of Materials through Instrumented Indentation with Reduced Sensitivity”, Acta Materialia, 55, 2025-2041, 2007. The current project has supported in part the research activities of two graduate students and one undergraduate student. Results A framework for assessing the issues of uniqueness and sensitivity associated with the indentation based methods of property extraction has been identified. A quantitative comparison of the sensitivity characteristics associated with the extraction of the elastic and plastic properties of materials through several combinations of multiple sharp indentations has been made. A new method for the determination of the elastic and plastic properties of materials through instrumented indentation with reduced sensitivity has been identified. BROAD IMPACT Fundamental Studies of Contact Fatigue in Metallic Materials T. A. Venkatesh, Tulane University, DMR 0547903 I 70 º 50 º To C 1 To C 2 To R w To S m I 70 º 50 º Sensitivity maps indicating domains of high sensitivity to experimental variability for dual indentation