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Failure of Beam Specimens (Examples). Notched Beams. 60- m m multi-axial fatigue device, the frequency was set to 23.885 kHz so that the amplitude at the end of the beam specimen was 1-2 μm. With the notch, a maximum von Mises stress of about 1.5 GPa was achieved at the notch.
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Failure of Beam Specimens (Examples) Notched Beams • 60-mm multi-axial fatigue device, the frequency was set to 23.885 kHz so that the amplitude at the end of the beam specimen was 1-2 μm. • With the notch, a maximum von Mises stress of about 1.5 GPa was achieved at the notch. • Failure occurred after approximately 8.3 x 108 cycles. Unnotched Beams • Two beam, 40 mm x 5 mm multi-axial fatigue device, • The amplitude at the end of the beam specimen was ~2 μm, yielding an equivalent stress of 2.80 GPa. • Failed after 2.14 x 105 cycles at 23.885 kHz • Crack occurs where predicted by FEM analysis • Smooth crack initiation site, brittle fracture
Stress – Lifetime Curve Stress-life results for polysilicon in vacuum conditions reveal a possible endurance limit for this material close to 1.5 GPa, in agreement with published data.