The 10 Essential Things you must do this summer!!!!!

Firstly, thanks to Pavel for the award, commiserations to my fellow conspirators.

Now, this thread has developed into an area, about which I do know a small amount.

The skiseekers article/binding maintenance/section 7, refers to fatigue in the binding spring.
Fatigue is a function of stress reversals, characterised by the stress reversal range and the number of reversal cycles. It is famously demonstated by the S-N curve, which is particular to specific materials.

Fatigue life is affected by other factors such as temperature, surface finish and residual stresses.

But.... the mode of failure by fatigue is by crack evolution, and fracture.

How many bindings in the world have failed by spring fracture?

Anyone?

I think they may have the failure terminology wrong. If not, then I think they are just wrong.

The most likely effect on a binding spring is creep. Creep affects all solids under load. A good analogy is the flow, under self weight of medieval glass. However, creep effectively exhibits at a reasonable elevated stress, (loading). This is markedly influenced by elevated temperatures, but that is not an issue for us.

So creep will affect our binding springs, the question is, to what extent. I discount the dynamic effects, (ie effects when we are actually skiing), because this is a relatively small percentage of the spring life. We are only really discussing the static effects, when the ski is in storage. Under low load, we might expect the spring to undergo creep, but that this will be very small, and for practical purposes not measurable.

The failure mode for creep is a reduced length, when under sustained compression, or vice versa for sustained tension. So, when the binding is not in use, but the spring is active, there will be creep, but in a well designed binding, this will not be measurable.

Man, I have just lost the will to live, I just want to point downhill.

Great explanation Dave

If I understand the effects of creep correctly, it would make the bindings release at a fractionally lower din setting than designed ?

That doesn't sound so terrible. I run my bindings on the minimum Din to do my type of skiing. I'm never in a "turn or die after this jump" situation, so I fgure a prerelease due to creep is not a major concern.

At the same time, if backing off the sping tension, then having it reset and tested befor the season makes you happy, then why not.

The benifit to all this talk, is that it gets people thinking about thier bindings. That's always a good thing.



Trencher

Spot on Trencher, creep wouold permanently change the spring length, and therefore it's resistance force. However, when the spring is at a low tension for an extended period of time, the creep effect would be minimal.

How minimal this is does depend on the ski binding design. If there is a spring that remains under a heavy tension when the binding is not in use, that would exhibit greater permanent deformation that a spring under lower tension.

I am not expert in binding design, so could not comment.

I used to set my bindings at DIN 5. My logic being that having a dodgy knee, I want to avoid a slow twisting throw-out with a higher setting. This changed when, on steep, heavy, wet off piste, the ski jammed into soft stuff, and I walked out of it. The loose ski then took off. The brake didn't work because the snow was soft, and I had a 300 metre hoof down on one ski. That night, I reset the Din to 7, where it has remained ever since.

I'm afraid to confess that I bench test my bindings by hitting the side of the boot sideways, so that I can "feel" the binding retention force.

Old habits......

My God....... :shock:

Dave Mac wrote:Fatigue life is affected by other factors such as temperature, surface finish and residual stresses.

But.... the mode of failure by fatigue is by crack evolution, and fracture.

How many bindings in the world have failed by spring fracture?

Anyone?

well put, I was going to ask the same question. Equally well put was the succinct definition of what fatigue is, better than I'd manage for sure :D The purpose of SN curves is help engineers select suitable materials for applications is it not? Which is why given it's well understood I struggle to understand why binding might contain the wrong springs.

In terms of fatigue, it struck me today driving down the hill, mind wandering, that corrosion would be another problem, I was particularly thinking of the effect of salt from the road if you're chucking the skis on the roof without any covering. Would that be right?

Trencher wrote:Great explanation Dave

If I understand the effects of creep correctly, it would make the bindings release at a fractionally lower din setting than designed ?

but hard to measure as Dave said, below the threshold that the binding test machine can manage from my limited field testing

Dave Mac wrote:
I used to set my bindings at DIN 5. My logic being that having a dodgy knee, I want to avoid a slow twisting throw-out with a higher setting. This changed when, on steep, heavy, wet off piste, the ski jammed into soft stuff, and I walked out of it. The loose ski then took off. The brake didn't work because the snow was soft, and I had a 300 metre hoof down on one ski. That night, I reset the Din to 7, where it has remained ever since.

ah, a direct hit on one of my many pet peeves :D I'm seriously wound up by the people who have their bindings set too low, after twice narrowly missing being hit in the head by loose skis and having one of the owners explain to me how is was "safer" to have the bindings low :D

ise wrote:

In terms of fatigue, it struck me today driving down the hill, mind wandering, that corrosion would be another problem, I was particularly thinking of the effect of salt from the road if you're chucking the skis on the roof without any covering. Would that be right?

Never mind whether the bindings work, How else are you going to show off your skis ? 8)

If mine are not inside the vehicle, then they're in the top box. The only problem I have with the top box is I tend to leave eguipment in there and the condensation is not good for gear.

Trencher

Ise,

Theoretically your thoughts on salt based corrosion have a murmuring of truth.

When the stress reversal situation is in air, the S-N curve flattens, lets say for a particular material at 300N/mm2. If this takes place in the presence of water, the base stress reduces to less than 200N/mm2. However, in a Sodium Chloride solution, there is no fatigue load base limit, and failure occurs at a much lower number of cycles.

But you have to remember, this is not an occasional skis-on-roof situation. This is a skis operating in the sea situation, it doesn't happen. And on your roof rack, stress reversals are not occuring, you ain't skiing at the same time.

I don't think that ski engineers would choose an incorrect spring material, so I agree with that.

When Pavel mentioned off-season spring relaxation, I thought it was a reasonable idea. I don't think that it does any harm.

Another empirical aspect to this discussion, relates to the nature of the individuals, and how much skiing they do. A few people on J2 are fortunate enough to do more than the regulation 2 weeks a year. Most of those, plus I am sure many others, ski at a fairly swift pace, for most of the time. In the event of a fall at speed, a Din 7 setting would pretty well ensure that the skis exploded away from you, quite desirable, should you be dilligent about keeping your edges sharp.

ise wrote: ah, a direct hit on one of my many pet peeves :D I'm seriously wound up by the people who have their bindings set too low, after twice narrowly missing being hit in the head by loose skis and having one of the owners explain to me how is was "safer" to have the bindings low :D

what about people that have their bindings set too high by the lovely chappy in the hire shop telling you "no you didn't put weight on over christmas" and then the skis didn't come off causing you ligament damage on both knees?

I curse the day I laughed at his "compliment".