a1 Department of Materials Science and Engineering, Stanford University, Stanford, California 94305
a2 Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305
a3 Department of Mechanical Engineering, Stanford University, Stanford, California 94305
a4 Department of Materials Science and Engineering, Stanford University, Stanford, California 94305
Although crystalline silicon is not generally considered susceptible to fatigue crack growth, recent studies suggest that there may be fatigue processes in silicon micro-machined structures. In the present study, a micro-machined fracture specimen geometry was used to examine stable crack growth under fatigue loading. Crack length and loads were carefully monitored throughout the test to distinguish between environmentally assisted crack growth (stress corrosion) and mechanically induced fatigue-crack growth. Results revealed similar steplike crack extension versus time for the cyclic and monotonic tests. The fatigue crack-growth curve extracted from the crack extension data exhibited a nearly vertical slope with no evidence of accelerated crack-growth rates. Fracture surfaces for the monotonic and cyclic tests were similar, further suggesting that a true mechanical fatigue crack-growth mechanism did not occur. Explanations for the observed lack of fatigue crack growth are presented and discussed with respect to reported stress-life behavior.
(Received January 13 2004)
(Accepted May 19 2004)
p1 Present address: A.M. Fitzgerald & Associates, 655 Skyway Rd. Suite 118, San Carlos, CA 94070.