Xie, Qiaoyun and Wosu, Sylvanus N
(2015)
CHARACTERIZATION of HIGH STRAIN RATE BEHAVIOR of TAC/CNTs/SIC CMCs PREPARED by SPARK PLASMA SINTERING.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Silicon carbide (SiC) ceramics are one of the best candidates for high temperature structural applications. However, due to the inherent drawbacks of hardness, porosity, and brittleness for ceramic materials and the specific application environment involving exposure to oxidation fuels, or aero heating, reinforcements of carbon nanotubes (CNTs) and tantalum carbide (TaC) are considered to improve the overall material properties; of particular interest are the fracture toughness, energy absorption ability, and oxidation resistance. Conventional fabrication of CNTs reinforced ceramic matrix composites (CMCs) involves hot pressing techniques, which are characterized by high pressure and a long processing time, but can destroy CNTs. The current research utilizes a rapid consolidation technique of spark plasma sintering (SPS) which densifies the ceramics at a relatively lower temperature and a much shorter holding time with improved bonding quality and finer microstructure.
A two-stage SPS of TaC and/or CNTs reinforced SiC CMCs was developed to investigate the sintering parameters, such as pressure, heating rate, and temperature on the densification behavior and mechanical properties. The oxidation mechanism of CNTs/SiC ceramics, as well as the TaC additives effect on the thermal oxidation resistance of the TaC/CNTs/SiC systems were examined up to 1500 oC. The influences of sample thickness, impact energy (loading rates), temperature and moisture on the compressive dynamic response of TaC and/or CNTs reinforced SiC CMCs were conducted by a penetration split Hopkinson pressure bar (P-SHPB). The fracture mechanics of TaC/CNTs/SiC CMCs were studied both quasi-statically and dynamically by Vickers indentation and a three point bending test on the modified SHPB with a pulse shaper. The possible toughening mechanisms provided by the CNTs reinforcement were directly observed. Wave propagation in SHPB was validated numerically and the prediction of damage evolution was carried out through user-defined material subroutine VUMAT in ABAQUS/explicit. The above investigations provide new perspectives which could impact a wide range of understandings and applications for the TaC/CNTs/SiC CMCs.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
9 June 2015 |
| Date Type: |
Publication |
| Defense Date: |
23 March 2015 |
| Approval Date: |
9 June 2015 |
| Submission Date: |
1 April 2015 |
| Access Restriction: |
2 year -- Restrict access to University of Pittsburgh for a period of 2 years. |
| Number of Pages: |
170 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Mechanical Engineering and Materials Science |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
SiC ceramics, carbon nanotubes, TaC additives, oxidation resistance, high strain rate, spark plasma sintering |
| Date Deposited: |
09 Jun 2015 15:19 |
| Last Modified: |
09 Jun 2017 05:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/24273 |
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