The discussion seems to assume the only important stress is longitudinal deformation, e.g., bending a long narrow plane during a carve, or skid or whatever. But IME, edge grip is more a function of torsional stiffness. Thus a plate often helps grip more dramatically than anything else. And AFAIK, any time we turn a ski, we also twist it, like a less dramatic version of wringing out a dishrag. Is some of the disagreement between physical models of longitudinal flex cycles and on-slope performance decrements due to not factoring in torsion?
Also, curious what "fatigue" is at a molecular level. I was under the impression that each flex cycle - whether wood or plastic or metal - causes some molecular chains to break or permanently deform. Over time, the accumulation of these microscopic damages will lead to macroscopic effects that we measure as failure to return to some original state, or I guess, actual shear like a bridge breaking in half. But if it's really linear accumulation of microscopic effects, then it's inaccurate to say that something will take x number of cycles to fatigue. Fatigue's just when the outcome crosses some threshold. Yes?
I ask because I'm curious whether the "100 day" rule of thumb, or whatever number of days we think our skis have in them has much to do with actual accumulated fatigue, or is just when it's so obvious that we notice. In biological systems, by the time the organism notices some loss of whole body functionality, usually a whole lot of damage has already been done.
Edited by beyond - 5/11/16 at 10:12pm