msepostdoc-list FW: SEMINAR NOTICE: O. Keles, PhD Final Exam, Tue. 4/2/13, 8:30 am, ARMS 1028

[Stacey, Lisa A]

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

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