Copper bonding wires are frequently used to connect to MEMS devices. Mechanical properties of copper wire are crucial to the reliability of MEMS system. The paper reported a symmetrical bending fatigue test on micron scale copper bonding wires. The test is based on the phenomenon that a micro-cantilever can be set into self-excited vibration between two electrodes under DC voltage. The results demonstrate that the yield strength, ultimate tensile strength and Young's modulus of copper wires with diameter of 20μm are higher than those with a diameter of 30μm and 40μm, which significantly performs size effect. In fatigue test, the number of cycles to failure is 104~107. Under the same stress condition, fatigue strength (N=106) of copper wires (d=20μm, 30μm, 40μm) is 140MPa, 97MPa, 70MPa respectively. The tensile fracture surface is the chisel-shaped peak, and the surface of the fracture appears many spaced strip drawing traces. The fatigue fracture surface is flat. Two cracks almost simultaneously originate from the surface, and the final rupture region is just like a narrow sheet.
In this study, carbon fiber reinforced polymer (CFRP) laminates that were under three-point bending load within and without initial impact damage, were detected and monitored by ultrasonic C-scan method. The defect morphology at various load levels was recorded. The dynamic monitoring for the growth of delaminations in CFRP laminates was acquired, and it provided an experimental evidence for the health monitoring on CFRP in service.
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