Repetitive impact testing of micromechanical structures

Abstract A micromechanical repetitive impact test apparatus made of polycrystalline silicon (polysilicon) has been designed, fabricated, and operated. The structure consists of two identical microimpact bumpers (MIBs), with impact masses of 3.7 × 10 −11 kg and impact bumper head radii of 30 μ. The two MIBs have been driven into resonance with impact at frequencies as high as 13.2 kHz. A nonlinear dynamic model of the impact system has been constructed using a traditional coefficient of restitution ( e ) assumption. Theory and simulation show that if the energies dissipated during impact are O J ( e = 1) and 1.6 × 10 −14 J ( e = 0.57), respectively, the amplitudes of the impact responses are 5.3 and 5.4 μm, respectively. Simulations demonstrate a ‘jump frequency’ highly dependent on the coefficient of restitution. In the structure described here, the coefficient of restitution was determined to be e = 0.57. Extended periods of impact to characterize possible wear have also been studied. In one test a maximum contact stress of 0.1 GPa was generated for 72 continuous hours. In another test, a maximum contact stress of over 2 GPa was generated for 12 continuous hours.

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