MSE Colloquium - Prof. Matt Miller, Cornell University
Date: February 11, 2011 from 2:00 pm to 3:00 pm EST
Location: Room 214 in S.W. Mudd.
Contact: For further information regarding this event, please contact Wesley Hattan by sending email to wjh2121@columbia.edu or by calling 2128547860.
Info: Click Here to Visit Website.
Bookmark and Share

Using High Energy X-ray Diffraction to Quantify the Micromechanical Behavior of Engineering Materials

 

Matthew P. Miller

Professor

Sibley School of Mechanical and Aerospace Engineering

Cornell University

 

Due to the lack of definitive understanding of mechanical processes on the size scale of an individual grain, design models for a process such as fatigue in polycrystals are still dominated by empiricism. Explicit representation of processes such as fatigue

crack initiation and microplasticity is often stated as the ultimate goal of many multiscale modeling efforts. Measuring the response on the size scale of the individual grain, however, has lagged model development. This lecture presents two experimental methods, both employing high energy synchrotron x-ray diffraction and in situ mechanical loading, for measuring the grain scale mechanical response of deforming polycrystals. The first experiment is a method for measuring lattice strain pole figures and determining distributions of stress over orientation space. These experiments were developed at the Cornell High Energy Synchrotron Source (CHESS) and currently include the ability to heat samples up to 1200oC while deforming them cyclicly. The High Energy Diffraction Microscopy (HEDM) suite of experiments at sector 1 of the Advanced Photon Source (APS) includes methods for measuring stress states of individual grains within a deforming polycrystal. Utilizing HEDM results with a finite element simulation (Conducted by Professor Paul Dawson from Cornell) to determine the single crystal elastic moduli of b21s, a bcc titanium alloy is also described. Finally, the process of transforming these diffraction experiments from one-off “heroic” efforts to true measurement capabilities – by quantifying resolution, sensitivity and uncertainty – is discussed.