Deformation modes
Posted: Tue Jun 10, 2008 8:03 pm
What I'm about to write is not guaranteed to be correct! I hope some engineers have some comments here. I'm just a geologist, so this elasticity stuff is a little foreign to me. (When rocks bend, they stay that way for millions of years!)
As I understand it (and I could be totally wrong here...) a ski can support nine different basic modes of deformation/vibration. They correspond to the three elastic moduli (Young's, shear and bulk) and the three principal axes. If you work through these nine modes in your head, you'll realize that non of them on their own really effect skis, which deform by composite modes (bending and torison). With the three principal axes (x = parallel to ski, y = vertical, z = perpendicular ski), there are six of these modes. Skis are way too stiff to bend around y, and forces that would cause bending around x just lead to torison. So the only bending mode is around z. Likewise, torison around y and z are just silly ideas, and a ski only twists around x. So I've identified the two deformation modes we're all familiar with, which we call longitudinal flex and torsion.
I'm curious if this makes any sense to anyone. And I'm wondering if there are other modes that can arise (not just in skis, but in general). Thanks.
As I understand it (and I could be totally wrong here...) a ski can support nine different basic modes of deformation/vibration. They correspond to the three elastic moduli (Young's, shear and bulk) and the three principal axes. If you work through these nine modes in your head, you'll realize that non of them on their own really effect skis, which deform by composite modes (bending and torison). With the three principal axes (x = parallel to ski, y = vertical, z = perpendicular ski), there are six of these modes. Skis are way too stiff to bend around y, and forces that would cause bending around x just lead to torison. So the only bending mode is around z. Likewise, torison around y and z are just silly ideas, and a ski only twists around x. So I've identified the two deformation modes we're all familiar with, which we call longitudinal flex and torsion.
I'm curious if this makes any sense to anyone. And I'm wondering if there are other modes that can arise (not just in skis, but in general). Thanks.