Size Effect of Cyclic Plasticity of Single-Crystal Copper: An In Situ SEM Bending Study

ABSTRACT

Cyclic mechanical loading is a critical factor leading to structural failure in microdevices/nanodevices. Given the widespread use of microbeam structures in movable components of microdevices, investigating their cyclic behavior under repeated bending is crucial. Therefore, three groups of single-crystal copper microbeams of different heights were fabricated using focused ion beam, and in situ cyclic bending experiments were performed in a scanning electron microscope to explore their complex plastic behavior. Results show that yield stress gradually decreases with increasing bending cycles due to strain gradient effects, with taller beams exhibiting a slower decline. The probability of burst size decreases gradually for microbeams of different heights in successive loading cycles, but the probability of burst size increases significantly in the final loading cycle due to the accumulation of dislocations near the neutral plane. These findings elucidate the influence of strain gradients in the size-dependent plastic deformation behavior of single-crystal copper microbeams.

Highlights

• In situ SEM cyclic bending tests were performed on single-crystal copper beams.
• Yield stress decreases with increasing beam height and number of bending cycles.
• The highest beam exhibits a wider burst size distribution.
• The burst size probability of each size beam varies notably in the last cycle.