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HYPERVELOCITY IMPACT DAMAGE IN ALUMINA
by
CHENG ZHANG
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MATERIALS SCIENCE)
August 2007
Copyright 2007 Cheng Zhang
Object Description
| Title | Hypervelocity impact damage in alumina |
| Author | Zhang, Cheng |
| Author email | chengz@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Materials Science |
| School | Viterbi School of Engineering |
| Date defended/completed | 2007-05-20 |
| Date submitted | 2007 |
| Restricted until | Restricted until 14 Aug. 2009. |
| Date published | 2009-08-14 |
| Advisor (committee chair) | Vashishta, Priya |
| Advisor (committee member) |
Madhukar, Anupam Mansfeld, Florian B. Kalia, Rajiv K. Nakano, Aiichiro |
| Abstract | Ceramics are important engineering materials for their outstanding hardness. One of the most widely used ceramics is alumina, a candidate for armor in defense and aerospace industry. Deformation and fracture mechanisms in alpha-alumina under hypervelocity impact up to 18km/s are investigated using molecular dynamics (MD) simulations containing 540-million atoms. Impacting projectile causes melting and local amorphization of the substrate in a spherical surrounding region. Away from the impact face, a wide range of deformations emerge and disappear under the influence of local stress fields, e.g., basal and pyramidal slips, basal and rhombohedral twins, which show good agreement with the experimental and theoretical results. Furthermore, new deformation modes such as twin along {0-111} are observed, and the relation between deformation patterns and local stress levels are probed. During unloading, micro-cracks nucleate extensively at the intersections of previous deformations. These micro-cracks grow and coalesce to form fractures under tensile stresses by the unloading wave. The substrate eventually fails along the surface of an hourglass-shaped region, when spallation ejects clusters of substrate material into the vacuum. We also carried out planar shock simulations of alpha-alumina single crystal and nanophase systems. The results show correlations between the atomistic deformation mechanisms and the elastic-plastic response of ceramic material observed in shock loading experiments. |
| Keyword | hypervelocity impact; deformation mechanisms; fracture mechanisms; alpha-alumina |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Type | texts |
| Legacy record ID | usctheses-m791 |
| Contributing entity | University of Southern California |
| Rights | Zhang, Cheng |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@dots.usc.edu |
| Filename | etd-Zhang-20070814 |
| Archival file | uscthesesreloadpub_Volume26/etd-Zhang-20070814.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@dots.usc.edu |
| Full text | HYPERVELOCITY IMPACT DAMAGE IN ALUMINA by CHENG ZHANG A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (MATERIALS SCIENCE) August 2007 Copyright 2007 Cheng Zhang |
