This paper presents the results of a study of the effect of cyclic loading parameters on the performance of piezo crystals. The output power of the crystals was observed to increase with parameters such as the cyclic frequency and the dynamic load range. However, the output power also decreased with increasing mean load. The efficiency of the crystal was calculated based on the mechanical energy applied to the piezo crystal. The ratio of the electrical output to mechanical energy input was taken as the efficiency of the crystal. This ratio was seen to increase with the cycling frequency, and also with the dynamic load range. However, increasing mean load caused the efficiency to drop significantly. The implications of the results are discussed for possible applications implanted bioMEMS and microelectronics systems.

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We have studied dynamic friction by impacting a copper plate onto a target consisting of a tapered, annealed, aluminium alloy plug mounted into a matching hole in a stainless steel outer sheath. The velocity of the back surface of the plug was measured using velocity interferometry. Unfortunately it was found that apparently identical configurations gave significantly different velocity profiles. Therefore a series of experiments were conducted in which the manufacturing tolerances were tightened and the assembly procedure was more carefully controlled than previously. Five experiments have been performed at the same impact velocity, (300m/s). Comparing the recent results with those fired previously it has become apparent that work hardening processes in the aluminium alloy near the sliding interface play an important role in the development of frictional forces. It is thought that work hardening generated at those regions of the cone surface in contact with the outer steel component during the assembly process leads to localised shear and, therefore, low friction when the system is loaded dynamically. By contrast those regions of the aluminium surface which remain soft give high friction following dynamic loading. We believe these effects explain the variability in the observed velocity traces.

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