Mechanical and Thermo-mechanical Fatigue Damage Evolution at Micro-scale

Monday, March 16, 2009
9:00 - 10:00 AM
Room 229, Norris Hall

Dr. Leila J. Ladani
Mechanical and Aerospace Engineering, Utah State University

Reliability is an essential element of materials used in aerospace, medical, and military applications regardless of scale. Poor reliability could lead to massive economic losses and place human lives at risk. A key aspect of reliability is determining the strength and durability of a material undergoing harsh environment or cyclic loading, such as extreme temperatures, temperature cycling, vibration or impact, which could result in early failure. Dynamic and rapid progress in engineering has resulted in new and advanced engineered materials with complex microstructures as well as materials engineered for small scales. Due to difference in manufacturing processes and microstructure, small scale material behave differently than bulk material. Testing and characterization of material at small scale involves many challenges such as specimen fabrication and gripping, applying force, and measuring strains. This talk will briefly summarize importance of reliability and application of material at small scale, and testing difficulties. A mechanism-based, anisotropic damage evolution model is developed using theoretical continuum damage mechanics and test of material. As an example of material used in micro-scale, pb-free solder which is commonly used as multifunctional material in microelectronic devices is investigated and damage model exponents are obtained using empirical technique. Another example is given where effect of voids on thermo-mechanical durability of microelectronic inter-connects was explored experimentally by developing error seeded specimens through implementation of an experiment on the process. Error-seeded specimens are then tested and monitored for failure under thermo-mechanical loading. Statistical and failure analysis is conducted to explore effect of process parameters on durability and void distribution and impact of voids on durability. The results of experiment are compared with modeling and simulation.

Biographical Sketch: Leila Ladani is currently assistant professor at Mechanical and Aerospace Engineering at Utah State University. She received her Master and PhD in Mechanical Engineering with specialty in material fatigue and damage from University of Maryland at College Park. Prior to that, she received Master degree with honor and Bachelor in Mechanical engineering from Isfahan University of Technology. Her research area involves characterization and testing of material at small scale. She explores micro-structural evolution and damage due to cyclic loading and fatigue for variety of applications such as electronic materials, materials for aerospace and biomaterials. She has several publications in the area of material and received several awards and honors for impact of her research, such as SMTA Hutchin’s award in 2005, Amelia Earhart award in 2006, APSIH Academic achievement award in 2007 and was recognized by University of Maryland and Noki company for her work through nomination for Harvard Society of Fellows and best project award

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