Mechanical Characterization of Materials At Micro/Nanoscale Under Bending

Abstract eng:
This paper presents a new method for testing materials at the micro/nanoscale under bending in-situ in SEM and TEM. The method consists of a straining stage with built-in force and displacement sensors. The sample is co-fabricated with the stage to eliminate any misalignment error. The method is applied to test the strength of silicon micro-beams under bending. The study reveals significant strengthening of silicon compared to that under uniform tension. This strengthening is contributed by stress localization near the surface of the beams close to the anchors, and the stress gradient from the surface to the neutral axis. Stress localization reduces the incidence of flaws that typically trigger premature fracture in the uniformly loaded samples, i.e., uniaxial tension. Most MEMS supporting beams are subjected to bending during operation. Their design landscape can be broadened by exploiting the effective strengthening of materials under bending — a paradigm that remains untapped to date.

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