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Schematic diagram of the bulge setup with a fixed guard-ringed electrode held from the membrane by a mechanical spacer. The membrane ( with of Al beam deposited on it) is bulged with nitrogen gas from the back while the front is maintained under vacuum. The change in capacitance between the bulged film and the fixed electrode indicates the height of the bulge.
(a) Aluminum stress and strain as a function of time for 30 min after a sudden bulging pressure step from 0 to 30 Torr. Relaxation of the stress is accompanied by an increase in strain as the bulge height increases with time. (b) Stress relaxation curves following sudden pressure increases to 20, 25, 30, and 35 Torr. (c) The effective modulus deduced from each of the four stress relaxation curves of (b) above. The four are essentially identical.
(a) Stress and strain in a Al film bulged suddenly with 30 Torr and held at constant bulge pressure for 1 h. (b) Stress and strain for the same film as (a) but bulged for 30 min after a sudden pressure step to 30 Torr followed by a sudden step down to 10 Torr and measured for another 30 min. (c) The time-dependent modulus deduced from the data of both (a) and (b) above using the iterative process described in the text. The two curves are essentially identical.
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