Passive vibration damping in an alpine ski by integration of shape memory alloys

Abstract

With exception of the wooden core, all the components of a modern alpine ski exhibit a decreasing vibration damping capacity with decreasing temperature. Although the damping effect of the wooden core is prevailing, the extreme hardness of snow under freezing conditions, at temperatures on low as -30°C, favours the appearance of vibrations which tend to make the skis more difficult to control. Therefore, the aim is to obtain a simple adaptive system to enhance vibrational damping at low temperatures, without spoiling the overall characteristics of the ski at higher temperatures. Shape memory alloys (SMA), in their low-temperature martensitic phase, exhibit a damping capacity which is orders of magnitude higher than in the standard materials of a ski. Transition from the SMA's high-temperature and low-damping austenitic phase to the high damping martensitic phase is achieved through a reversible thermally induced martensitic phase transformation (MPT). In this project, CuZnAl plates have been integrated into the complex sandwich structure of an alpine ski. Three point bending and differential scanning calorimetry (DSC) have been used to characterise the materials and their effects on the damping behauvour. In order to ensure the most efficient damping through shear deformations, an excellent adherence between the SMA plates and other materials has to be guaranteed by means of a surface treatment including sand blasting and chemical etching. The damping effect also depends on the location of the SMA plates within the ski. First tests on modified full-size alpine skis have already illustrated the improvements in damping capacity achieved with the integration of CuZnAl elements.