Christopher L. Muhlstein

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When subjected to alternating stresses, most materials degrade, e.g., suffer premature failure, due to a phenomenon known as fatigue. It is generally accepted that in brittle materials, such as ceramics, fatigue can only take place in toughened solids, i.e., premature fatigue failure would not be expected in materials such as single crystal silicon. The(More)
A study has been made to discern the mechanisms for the delayed failure of 2-μm thick structural films of n+-type, polycrystalline silicon under high-cycle fatigue loading conditions. Such polycrystalline silicon films are used in smallscale structural applications including microelectromechanical systems (MEMS) and are known to display ‘metal-like’(More)
Although bulk silicon is not known to exhibit susceptibility to cyclic fatigue, micron-scale structures made from silicon films are known to be vulnerable to degradation by fatigue in ambient air environments, a phenomenon that has been recently modeled in terms of a mechanism of sequential oxidation and stress-corrosion cracking of the native oxide layer.(More)
Bulk silicon is not susceptible to high-cycle fatigue but micron-scale silicon films are. Using polysilicon resonators to determine stress-lifetime fatigue behavior in several environments, oxide layers are found to show up to four-fold thickening after cycling, which is not seen after monotonic loading or after cycling in vacuo.We believe that the(More)
Ovarian pregnancies usually are diagnosed by the trophoblast which has gone into the ovarian tissue being found histologically. These pregnancies usually suggest haemorrhage from the corpus luteum or a rupture of ovarian cysts. The average age at which they appear is 29, just as it is the age for tubal pregnancies, but they do differ because there are few(More)
The surfaces of worn components hold clues to the underlying wear mechanisms. Previous evidence suggested that the absolute wear rates of acetabular components in a hip simulator were related to mechanical behavior; we hypothesized that the surface morphology of the liners might also be sensitive to mechanical properties. A noncontact, three-dimensional(More)
Free-standing mesoscale (340 mum x 30 mum x 20 mum) bend bars with an aspect ratio over 15:1 and an edge resolution as fine as a single grain diameter ( approximately 400 nm) have been fabricated in large numbers on refractory ceramic substrates by combining a novel powder processing approach with photoresist molds and an innovative lost-mold thermal(More)
It is known that micron-scale polycrystalline silicon thin films can fail in room air under high frequency (40kHz) cyclic loading at fully-reversed stress amplitudes as low as half the fracture strength, with fatigue lives in excess of 1011 cycles. This behavior has been attributed to the sequential oxidation of the silicon and environmentally-assisted(More)
When subjected to alternating stresses, most materials degrade, e.g., suffer premature failure, due to a phenomenon known as fatigue. It is generally accepted that in brittle materials, such as ceramics, cyclic fatigue can only take place where there is some degree of toughening, implying that premature fatigue failure would not be expected in(More)
To evaluate the long-term durability properties of materials for microelectromechanical systems (MEMS), the stress-life (S/N) cyclic fatigue behavior of a 2-mm thick polycrystalline silicon ®lm was evaluated in laboratory air using an electrostatically actuated notched cantilever beam resonator. A total of 28 specimens were tested for failure under high(More)