Fatigue crack growth behavior of a titanium matrix composite under thermomechanical loading
Abstract
The fatigue crack growth characteristics of a 4-ply, unidirectional, titanium matrix composite, SCS-6/Ti-6Al-2Sn-4Zr-2Mo, subjected to thermo-mechanical loading was investigated. The majority of work conducted for this research project was of an experimental nature. A test frame was assembled to perform the fully-automated, computer-controlled thermomechanical fatigue crack growth tests. A series of isothermal, in-phase, and out-of-phase crack growth tests were run. The test temperatures ranged from 150$\sp\circ$C to 538$\sp\circ$C and the fastest thermal frequency was 0.0083 Hz. The baseline isothermal and TMF data suggested that the time-at-temperature and the maximum temperature experienced by the composite significantly influenced the fatigue crack growth rates. Isothermal conditions produced higher crack growth rates than either in-phase or out-of-phase conditions for equivalent mechanical frequencies. Fiber bridging during both the isothermal and TMF tests was limited to a region of approximately 2-3 fibers directly behind the advancing crack tip. A linear summation approach was developed to model the effect of isothermal and thermomechanical cycling on the crack growth rates of the SCS-6/Ti-6Al-2Sn-4Zr-2Mo composite. The total fatigue crack growth rate was decomposed into cycle-dependent and time-dependent components. The model was able to correlate all the baseline fatigue crack growth tests as well predict the fatigue crack growth rate of a test which began under isothermal conditions and ended under in-phase conditions.
Degree
Ph.D.
Advisors
Grandt, Purdue University.
Subject Area
Aerospace materials|Mechanical engineering|Materials science
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.