Date of Award
Doctor of Philosophy
Materials Science and Engineering
The Young's modulus of polycrystalline Al(,2)O(,3), Gd(,2)O(,3), and MgTi(,2)O(,5) was measured as a function of temperature. Hysteresis between heating and cooling data was observed for all of the Gd(,2)O(,3) and MgTi(,2)O(,5) specimens, and for the Al(,2)O(,3) specimens having the largest grain size. The observed hysteresis is attributed to the opening of microcracks during cooling and to crack closure during heating;A theoretical model was developed to describe T(,MB), the temperature at which microcracking begins, as a function of grain size. The Cleveland-Bradt equation for critical grain size was also extended so that it could be compared to the model developed in this study. For each of the three materials studied, the slope of T(,MB) versus grain size agreed relatively well with that predicted by the model, to within a multiplicative constant of about 1.7162. The extended Cleveland-Bradt equation fit the data less well;A graphical method of predicting critical grain size was also demonstrated;('1)This research was supported by the Engineering Research Institute of Iowa State University through funds provided by the National Science Foundation under Grant No. DMR 78-01584.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Eldon Darrel Case
Case, Eldon Darrel, "Grain size dependence of microcrack initiation in brittle materials " (1980). Retrospective Theses and Dissertations. 6687.