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Do edge cracks ever occur because of tension from the ski flexing?
Only the thin middle layer of a ski is going to not feel tension/compression when the ski bends/flexes. The edges on the bottom are going to experience compression when the tip and tail of the ski flex downwards, but more importantly the edges will experience tension when the tip and tail are flexed upwards. Can this tension snap the edge and cause an edge crack? How do ski makers build skis so that the different layers are elastic/flexible enough to deal with differential amounts of stretching/compressing from the base to the topsheet? Are the glues they use elastic?
WoFlowzDigging the content lately Dolan. Ever think of a job at a ski company in the R&D areas
I do think about it alot. Id be stoked to intern at a ski companys engineering dept, to learn the ropes enough i could contribute or start building my own skis. I think school wise id want a structural engineering program buf it would be cool if there was one catered to like sports equipment and materials science.
DolansLebensraumI do think about it alot. Id be stoked to intern at a ski companys engineering dept, to learn the ropes enough i could contribute or start building my own skis. I think school wise id want a structural engineering program buf it would be cool if there was one catered to like sports equipment and materials science.
materials science is really interesting.
i could see you being a very annoying intern to be honest, in a good way though. just someone that would ask ten billion questions
I'm gonna think about it more tomorrow, but my first guess is that skis are thin enough for the tension/compression from the bending force to be insignificant. The more of an object's cross sectional area is further away from the central axis, the greater these forces will be. With a ski, the entire cross section is distributed very close to the x-axis at its center so the tension and compression would be very small. Cool question
**This post was edited on Mar 3rd 2021 at 1:10:36am
DolansLebensraumOnly the thin middle layer of a ski is going to not feel tension/compression when the ski bends/flexes. The edges on the bottom are going to experience compression when the tip and tail of the ski flex downwards, but more importantly the edges will experience tension when the tip and tail are flexed upwards. Can this tension snap the edge and cause an edge crack? How do ski makers build skis so that the different layers are elastic/flexible enough to deal with differential amounts of stretching/compressing from the base to the topsheet? Are the glues they use elastic?
Yes, only a small point will not feel tension or compression. This is called the neutral axis. Then we get bending moments involved along with shear forces, tension, stress, and strain. Shout out to my mechanics of materials class lol
I don’t think you could ever get an edge crack from the ski flexing. You be likely to sheer the layers of the ski first before reaching the ultimate fail point of the steel. Ie one layer sliding forward and thus shearing the bond between materials and causing a delam. Edges are made of thin gage steel right? It seems like the core of ski has a lower fracture point than does steel.
Most if not all normal flexions would still be in the steels elastic region, thus causing no harm.
When I’ve snapped skis before the edges were really flexible. Someone who actually builds skis can chime in here.
forgive any typos, it’s midnight and I’m hammering away here on mobile lol
DolansLebensraumI do think about it alot. Id be stoked to intern at a ski companys engineering dept, to learn the ropes enough i could contribute or start building my own skis. I think school wise id want a structural engineering program buf it would be cool if there was one catered to like sports equipment and materials science.
materials science is really interesting.
Materials science is the future of all engineering man. Do it. If it wasn't too boring to me I for sure would. I'm just going to be one of the first ones using the material scientists' work.
In terms of the edges under tension, that thin amount of metal is totally fine bending the amount it does. Think about how much it moves, even on a soft ski. The amount it moves from where it wants to be is called strain and in long thin beams, which you can effectively call a ski edge, it's directly related to the length. A 180 cm long edge is probably only moving ±15 cm during regular use, which is 1/12 the length. Pretty insignificant when the benefit of most metals are their ability to flex a little bit without losing strength. It's more likely edge cracks are just from heavy impacts, especially when it's cold out.
**This post was edited on Mar 3rd 2021 at 1:30:33am
The steel used in ski edges is "tempered" so it can withstand a huge amount of stress, and flex without actually deforming (similar to a high quality knife). If the core of the ski cracks or snaps the edge might "kink" a bit, but at that point your ski is already gone. The biggest problems with edges is delamination from the other materials as epoxy can't actually "soak" into the edge, so over time lots of flexing can cause them to separate.
The real strength of a ski comes from the of Epoxy Resin and Layers of "Triaxial" fiberglass and other composite layers like carbon fiber etc.. Of course the profile and material of the ski core effects breaking strength, and flex patterns but overall the composite layers and epoxy are what bonds the ski together, and gives them elasticity.
byuboundI'm gonna think about it more tomorrow, but my first guess is that skis are thin enough for the tension/compression from the bending force to be insignificant. The more of an object's cross sectional area is further away from the central axis, the greater these forces will be. With a ski, the entire cross section is distributed very close to the x-axis at its center so the tension and compression would be very small. Cool question
**This post was edited on Mar 3rd 2021 at 1:10:36am
Ok yeah here is a little quick math that would back this up:
Imagine if you are flexing a ski hard, you are creating an arc with a radius of maybe 2 meters (Probably larger but I don't really care to check)
Say our ski has an edge length of like 185 cm, so the arc length would be 185 cm at the cross section of the ski.
Assume the ski at its thickest point is 1 cm thick, so assuming a rectangular cross section for simplicity's sake the distance from the centroid to the base would be .5 cm.
(1.85/(2(2)*pi))*(2.005(2)pi)=1.855m.
Each edge of the ski would experience an elongation of .5 cm, which is a strain of .5/185=.0027.
This would be well below the point of ultimate failure shown on the diagram shinbang posted.
Most certainly. Sometimes I’ll see edge cracks near the tip/tail and think hmm how did that get there. I think most of the time though the epoxy between the edge tabs give out first and the edge just moves. That’s why you get edge ripouts near tip and tail.
in other words, if your ski has edge cracks as a result of flexing, the ski manufacturer is doing a really good job of making sure those edge tabs stay in solid.
weastcoastMost certainly. Sometimes I’ll see edge cracks near the tip/tail and think hmm how did that get there. I think most of the time though the epoxy between the edge tabs give out first and the edge just moves. That’s why you get edge ripouts near tip and tail.
in other words, if your ski has edge cracks as a result of flexing, the ski manufacturer is doing a really good job of making sure those edge tabs stay in solid.
Hate to tell ya but those cracks aren't from flexing. Probably hitting stuff or even each other.
weastcoastAs In “by tip and tail” I mean like halfway between mid-ski and the end. But idk, usually when I hit stuff I just get edge dents.
Yeah when metal is warmer it is more ductile and will dent but if it gets too cold and/or too concentrated a force, it is more likely to crack. Likely there are already microtears in the steel lattice and the visible cracks probably grow from these.
ReturnToMonkeyYeah when metal is warmer it is more ductile and will dent but if it gets too cold and/or too concentrated a force, it is more likely to crack. Likely there are already microtears in the steel lattice and the visible cracks probably grow from these.
Makes sense, since this season has been the coldest PA season I’ve ever skied in my 12 years of skiing
I was wondering about this. I was skiing some really cold temps this winter and nabbed two edge cracks pretty early on. Previously, I had usually skied park in warmer places and edge cracks weren’t as much of an issue for me (I also had a professionally done, aggressive detune)
ReturnToMonkeyYeah when metal is warmer it is more ductile and will dent but if it gets too cold and/or too concentrated a force, it is more likely to crack. Likely there are already microtears in the steel lattice and the visible cracks probably grow from these.
BradFiAusNzCoCaI was wondering about this. I was skiing some really cold temps this winter and nabbed two edge cracks pretty early on. Previously, I had usually skied park in warmer places and edge cracks weren’t as much of an issue for me (I also had a professionally done, aggressive detune)
Generally, steel has a DBTT of about -20°F but it's more of a region than a set temp. Here's a pretty basic graphic of what I'm talking about.
So, in theory, as I hit them against rails at colder temps - they are more prone to cracking as the absorb less energy. Correct?
ReturnToMonkeyGenerally, steel has a DBTT of about -20°F but it's more of a region than a set temp. Here's a pretty basic graphic of what I'm talking about.
BradFiAusNzCoCaSo, in theory, as I hit them against rails at colder temps - they are more prone to cracking as the absorb less energy. Correct?
Yeah, at a basic level that's a better way to explain it. But really what's happening is the energy isn't being absorbed in the form of deforming the metal, but rather it is being used to separate the bonds between molecules, causing a crack. At higher temps, the bonds have more energy (temperature = energy) so they can move a bit without separating. At lower temps they can't resist the movement as much.
So, in theory, could you prolong edges by only riding rails on warmer days and avoiding them on the cold ones?
ReturnToMonkeyYeah, at a basic level that's a better way to explain it. But really what's happening is the energy isn't being absorbed in the form of deforming the metal, but rather it is being used to separate the bonds between molecules, causing a crack. At higher temps, the bonds have more energy (temperature = energy) so they can move a bit without separating. At lower temps they can't resist the movement as much.
BradFiAusNzCoCaSo, in theory, could you prolong edges by only riding rails on warmer days and avoiding them on the cold ones?
Yeah that would likely make them last longer but there's also a lot more factors. For example I know I typically send harder on warmer days so I probably would be putting heavier impacts on the edges.
byuboundOk yeah here is a little quick math that would back this up:
Imagine if you are flexing a ski hard, you are creating an arc with a radius of maybe 2 meters (Probably larger but I don't really care to check)
Say our ski has an edge length of like 185 cm, so the arc length would be 185 cm at the cross section of the ski.
Assume the ski at its thickest point is 1 cm thick, so assuming a rectangular cross section for simplicity's sake the distance from the centroid to the base would be .5 cm.
(1.85/(2(2)*pi))*(2.005(2)pi)=1.855m.
Each edge of the ski would experience an elongation of .5 cm, which is a strain of .5/185=.0027.
This would be well below the point of ultimate failure shown on the diagram shinbang posted.
Nice maths. Makes sense. I think a few ppl here are thinking we are talking about the edge cracking because of just the bending that occurs when a ski flexes, but i just wanted them to know we were talking about the tension and compression that would occur on different layers of the ski when it flexed. For example, try to bend a cookie by raising either end of it. The crack in the cookie will be at the bottom first, and at the top of the cookie there will be compression, just based on the geometry. Of course taking a naked ski edge and simply bending it would be totally within stress limits and the edge would never snap from just that, probly not even when the temp is very low.
I didnt know that steel was actually that elastic along its length. I thought as soon as a steel rod or beam or rail started stretching it would be non-elastic and induce permanent deformation (stretching).
its cool to know that unless you bashing your skis on rails its unlikely that you will get edge cracks.
ReturnToMonkeyGenerally, steel has a DBTT of about -20°F but it's more of a region than a set temp. Here's a pretty basic graphic of what I'm talking about.
Damn. More reason not to ski when its cold as fuck outside.
DolansLebensraumI do think about it alot. Id be stoked to intern at a ski companys engineering dept, to learn the ropes enough i could contribute or start building my own skis. I think school wise id want a structural engineering program buf it would be cool if there was one catered to like sports equipment and materials science.
materials science is really interesting.
I thought material science would be cool. You just learn about what point shit breaks at. It’s so boring. Interesting applications but the actual work is terrible.
J_Mendez2001I thought material science would be cool. You just learn about what point shit breaks at. It’s so boring. Interesting applications but the actual work is terrible.
Awe. Yeah i can see it sounding more romantic than it ends up being.
J_Mendez2001I thought material science would be cool. You just learn about what point shit breaks at. It’s so boring. Interesting applications but the actual work is terrible.
I can’t tell you how many hundreds of pages of engineering paper I’ve gone through. Lots of calculations for that class. Just gotta grind through it bro.
J_Mendez2001I thought material science would be cool. You just learn about what point shit breaks at. It’s so boring. Interesting applications but the actual work is terrible.
shin-bangI can’t tell you how many hundreds of pages of engineering paper I’ve gone through. Lots of calculations for that class. Just gotta grind through it bro.
Eh just one or two classes doesn't fully represent what the industry of material science is like. There's a lot more cool things you do and also, tons of computer access to make calculations. School is definitely different than the industry.
ReturnToMonkeyEh just one or two classes doesn't fully represent what the industry of material science is like. There's a lot more cool things you do and also, tons of computer access to make calculations. School is definitely different than the industry.
Hence why I said *class*
Having worked/working in the industry that I’m majoring in, sadly things are pretty different.
again, you just gotta grind through the classes to get the prize.
I feel like there has to be a new way of making skis that will give a bulletproof edge durability.
I dont know how you can have fun skiing when your edges are fubar. For me at least it would bother the fuck out of me. Busted edges are like busted ravioli. No. Just no.
DolansLebensraumI feel like there has to be a new way of making skis that will give a bulletproof edge durability.
I dont know how you can have fun skiing when your edges are fubar. For me at least it would bother the fuck out of me. Busted edges are like busted ravioli. No. Just no.
I mean there are certainly better metals, but skis are already expensive as is. Cost ultimately has the final say in designs and common steels are cheap and easy to produce/work on. Also I'd say edge problems are less common than like top sheet delam, sidewall blowouts, core shots, and snapped skis, so putting R&D into the edges probably doesn't have enough return on investment.
**This post was edited on Mar 4th 2021 at 8:06:34pm
The money from extensive R&D has resulted in.... no edges lol
I am curious to see how those ON3Ps with no edge underfoot (that Forster Meeks teased) go
ReturnToMonkeyI mean there are certainly better metals, but skis are already expensive as is. Cost ultimately has the final say in designs and common steels are cheap and easy to produce/work on. Also I'd say edge problems are less common than like top sheet delam, sidewall blowouts, core shots, and snapped skis, so putting R&D into the edges probably doesn't have enough return on investment.
**This post was edited on Mar 4th 2021 at 8:06:34pm
DolansLebensraumOnly the thin middle layer of a ski is going to not feel tension/compression when the ski bends/flexes. The edges on the bottom are going to experience compression when the tip and tail of the ski flex downwards, but more importantly the edges will experience tension when the tip and tail are flexed upwards. Can this tension snap the edge and cause an edge crack? How do ski makers build skis so that the different layers are elastic/flexible enough to deal with differential amounts of stretching/compressing from the base to the topsheet? Are the glues they use elastic?
I didn´t experience any edge crack because of bending my skis. But what I´ve experienced from bending my skis while buttering is that the top sheet came off due to the compression of the most upper layer (top sheet). This happened to me for the third time. Three seasons in a row. The first two times with the Lib Tech UFO 100 and 105. The third time I went for the Line Sakana (not intentionally a ski for buttering, but I personally love a short radius combined with some playfulness) and it just blew up at the tip.
ReturnToMonkeyI mean there are certainly better metals, but skis are already expensive as is. Cost ultimately has the final say in designs and common steels are cheap and easy to produce/work on. Also I'd say edge problems are less common than like top sheet delam, sidewall blowouts, core shots, and snapped skis, so putting R&D into the edges probably doesn't have enough return on investment.
**This post was edited on Mar 4th 2021 at 8:06:34pm
Thats crazy. Edge damage is the only damage ive ever had on a pair of my skis.
instisigramI didn´t experience any edge crack because of bending my skis. But what I´ve experienced from bending my skis while buttering is that the top sheet came off due to the compression of the most upper layer (top sheet). This happened to me for the third time. Three seasons in a row. The first two times with the Lib Tech UFO 100 and 105. The third time I went for the Line Sakana (not intentionally a ski for buttering, but I personally love a short radius combined with some playfulness) and it just blew up at the tip.
Damn. That sucks. Maybe its the upper layers that compress when a ski flexes more so than the edges stretching.
