Photo elastic analysis of ice-axe impacts

This paper outlines a project to study the dynamic loading of ice-axes. The principle aim of the research was to increase the understanding of the state of stress experienced by an ice-axe in normal use. A climber's overarm swing technique, as employed in technical 'ice-climbing', was studied using a high speed video system. A typical swing was found to have an impact velocity of 90 ms-1 at a pick impact of 20° to the normal. A test rig was constructed to replicate the dynamic loading of a selection of 'technical axe' heads. A 2 mm thick photoelastic coating was bonded to each of the pick faces and impact events recorded using a reflection polariscope and a high speed video running at 2000 frames per second. The observed fringe patterns were used to make a qualitative comparison between picks with different tooth designs - saw-toothed, 6 mm and 45 mm semi-circular toothed and plain picks. It was found that the loading was predominantly in-plane bending in-plane bending. Improvements in strength performance could most effectively be achieved by widening and not thickening of the pick. However, the loading is unlikely to be that in which might be a combination of out of plane bending and torsion. It was concluded, therefore, that a study needs to be carried out to look at the loading regime in realistic conditions.