TAM Seminar Series Presents

Speaker: Jia-Liang Le

University of Minnesota

Host: Professor Zdenek Bazant

AbstractIt is widely acknowledged that no structures can be designed to be risk free, and therefore reliability analysis plays a central role in the design of engineering structures. The recent focus has been placed on structures made of brittle heterogenous (a.k.a. quasibrittle) materials, such as ceramics, composites, concrete, and many more at the microscale. We recently developed a level excursion model for analyzing the probabilistic failure of quasibrittle structures, in which the structural failure statistics is calculated as a first passage probability. The main feature of the model is that it captures both the spatial randomness of local material resistance and the random stress field induced by microstructures (e.g. randomly distributed flaws). It is shown that the model represents a continuum generalization of the classical weakest-link model, which recovers the Weibull distribution as an asymptotic distribution function. In this talk, I will discuss two applications of this model:1) Modeling of strength distribution of polycrystalline silicon (poly-Si) MEMS structures based on 1D level excursion analysis. We show that the model agrees well with the experimentally measured strength distributions of poly-Si MEMS specimens of different sizes. The model predicts a complete size effect curve of the mean structural strength, which transitions from a vanishing size effect at the small-size limit to the classical Weibull size effect at the large-size limit.2) Investigation of the tail distribution of strength of brittle and quasibrittle structures by extending the level excursion analysis to high dimensions. We show that the power-law tail distribution of structural strength stems from the tail distribution of material strength. Flaw statistics introduces additional randomness to the overall failure statistics of the structure, but does not dictate the power-law form of its tail distribution.

BiographyDr. Jia-Liang Le is currently an associate professor in the Department of Civil, Environmental, and Geo- Engineering at the University of Minnesota. He earned his Bachelor of Engineering (First Class Honors) and Master of Engineering from the National University of Singapore, and a Ph.D. in structural engineering from Northwestern University. He is a registered professional engineer and a member of ASCE, ACI and SES. His research interests include fracture mechanics, probabilistic mechanics, scaling, computational mechanics, and structural reliability. He received the Army Research Office Young Investigator Award, the EMI Leonardo da Vinci Award from the American Society of Civil Engineers, and the Society of Engineering Sciences Young Investigator Medal.