MATERIALS SCIENCE AND ENGINEERING SEMINAR Modeling Failure of Brittle Porous Ceramics By: Özgür Keleş Ph.D. Final Examination Co-Advisors: Prof. R. E. Garcia & K. J. Bowman ABSTRACT Brittle porous materials (BPMs) are used for battery, fuel cell, catalyst, membrane, filter, bone graft, and pharmacy applications due to the multi-functionality of their underlying porosity. However, in spite of its technological benefits the effects of porosity on BPM fracture strength and Weibull statistics are not fully understood--limiting a wider use. In this context, a two-dimensional finite element (FE) simulation-based approach was developed to assess the pore--pore interactions and their impact on fracture statistics of isotropic microstructures. The classical fracture mechanics approach was combined with FE simulations that account for the interactions to predict the decrease in the fracture stress with increasing porosity. Simulations show that even the microstructures with the same porosity level and size of pores differ substantially in fracture strength. The maximum reliability of BPMs was shown to be limited by the underlying pore--pore interactions. BPM fracture strength decreases at a faster rate under biaxial loading than under uniaxial loading. Three different types of deviation from classic Weibull behavior are identified: P-type corresponding to a positive lower tail deviation, N-type corresponding to a negative lower tail deviation, and S-type corresponding to both positive upper and lower tail deviations. Pore-pore interactions result in either P-type or N-type deviation in the limit of low porosity. Whereas, S-type behavior occurs when clusters of low and high fracture strengths coexist in a fracture data. Date: Tuesday, April 2, 2013 Time: 8:30 A.M. Place: ARMS 1028 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100