Structural optimization of classic and skating skirolls after field testing

Modern skirolls are made of composite materials or combinations of metal and plastic parts. Aims of the present work were: i) the acquisition of field load spectra on instrumented skirolls; ii) the fatigue life prediction of modern skirolls after constant amplitude fatigue testing; iii) the structural optimisation of the skirolls and the redesign for a target mission. Two pairs of traditional aluminium skirolls were strain gauged in order to measure the bending actions in the vertical and horizontal planes: two full bridge measured the vertical plane bending at two different locations, whereas two half bridges applied at the two wheel supports measured the lateral loads. A rugged data acquisition system was used to record several sessions of classical and skating technique on four elite and amateur athletes. The system allowed to measure the instantaneous load values and positions during the push phases: typical load patterns were obtained and peak values were normalised to the testers body weight giving 125% B.W. in the classical technique and 137% B.W. in the skating technique. Field load spectra were collected during typical ski sessions and compared with fatigue test data from a fatigue test bench at DolomitiCert laboratory. The knowledge of in field load spectra and the skiroll fatigue curves allowed to perform the fatigue life prediction of the existing skirolls and to compare it with a target mission. A solid model of each skiroll was reconstructed with ProE® and FEM analysed with Ansys®. The finite elements model was validated comparing the results of the simulation with the laboratory tests. A new optimised profile of the skiroll was developed in order to get a uniform permissible bending stress. With this new profile the fatigue life increased of 20 times with a mass increment of only 6% per skiroll.