 Poster: A snowHead
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| petemillis wrote: |
| Why did the chair have 3 people on it whenAspen limits the number to 2? |
2 American skiers = same weight as 3 European skiers? 
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| ssh wrote: |
It is a result of normal stress over time. This is why they do complete inspections at the intervals that they do. The components do wear and stress and will fail if they are not repaired or replaced as they age. As I understand it, they do not replace every component on a regular interval but rather rely on the inspections. I assume (but haven't asked so don't know) that they have a maximum lifetime at which they will replace the components.
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The fatigue life of components depends on the design reserve factor. It could be years or practically infinite. Which doesn't imply that regular inspection is not required. Cracks can propagate for many reasons, often leading to premature failure if not discovered in time. As I'm sure you are aware, most failures of this nature occur around welded joints or sharp edges.
| ssh wrote: |
Do you mean to imply that the components should work flawlessly for an indeterminate period? (I know you don't mean that!) If not, though, it makes sense that there will be failure at some point if the components are not repaired/replaced. Some of the components, of course, will fail before the MTBF and perhaps before the expected time range. |
It would be highly likely in this case that the design reserve factor was high enough to give practically infinite fatigue life. Any premature failure would be the result of a material or manufacturing defect, damage, corrosion or extreme overloading. To state that the failure was simply due to the stress of routine loading is an admission of negligence in my book - either in design (reserve factor too low) or maintenance (component not replaced at specified design interval).
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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| veeeight wrote: |
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I work in F1 where we walk a very thin line when it comes to fatigue life of safety critical components
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And yet I have seen numerous examples of "lash together" jobs in F1 too!  |
The days of "lash ups" are long gone when it comes to safety critical components. The game has changed a lot in the last decade. It's gone from a cottage industry to full blown aerospace level quality control. Despite designs becoming increasingly marginal in search of performance, failure of safety related items is now actually quite rare. Trackside "Lash ups" still occur in non-critical situations eg increased cooling for electrical boxes in Malaysia.
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You need to Login to know who's really who.
You need to Login to know who's really who.
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uktrailmonster, I don't doubt that things have improved over the last few years. I used to work with many a F1 engineer, when they came over to our side of the fence (OE) - they would (and still are) be amazed at the product development and validation that vehicles with a 12+ year lifecycle had to be put through, processes that are still *much* more thorough that F1.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| uktrailmonster wrote: |
| ssh wrote: |
It is a result of normal stress over time. This is why they do complete inspections at the intervals that they do. The components do wear and stress and will fail if they are not repaired or replaced as they age. As I understand it, they do not replace every component on a regular interval but rather rely on the inspections. I assume (but haven't asked so don't know) that they have a maximum lifetime at which they will replace the components.
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The fatigue life of components depends on the design reserve factor. It could be years or practically infinite. Which doesn't imply that regular inspection is not required. Cracks can propagate for many reasons, often leading to premature failure if not discovered in time. As I'm sure you are aware, most failures of this nature occur around welded joints or sharp edges. |
Agreed. Since this failure didn't occur at a weld, an educated guess would be that it was a material failure that was unexpected.
| uktrailmonster wrote: |
| ssh wrote: |
Do you mean to imply that the components should work flawlessly for an indeterminate period? (I know you don't mean that!) If not, though, it makes sense that there will be failure at some point if the components are not repaired/replaced. Some of the components, of course, will fail before the MTBF and perhaps before the expected time range. |
It would be highly likely in this case that the design reserve factor was high enough to give practically infinite fatigue life. Any premature failure would be the result of a material or manufacturing defect, damage, corrosion or extreme overloading. To state that the failure was simply due to the stress of routine loading is an admission of negligence in my book - either in design (reserve factor too low) or maintenance (component not replaced at specified design interval). |
Or an unexpected error in material composition (which I think it likely in this case). My point being that just because it happened doesn't mean that it's anyone's fault or that we should go looking for a scapegoat.
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You'll need to Register first of course.
You'll need to Register first of course.
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| ssh wrote: |
| ............Or an unexpected error in material composition (which I think it likely in this case). My point being that just because it happened doesn't mean that it's anyone's fault or that we should go looking for a scapegoat. |
An unexpected error in material composition is a quality failure. In which case someone is at fault. Either the right material was not specified with its associated standard, or the right material was not supplied.
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What about a bubble in the casting?
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petemillis, are you suggesting that forging would be more appropriate than casting? May already be done in [edit] appropriate [/edit] critical components.
Last edited by After all it is free  on Tue 17-04-07 17:53; edited 1 time in total
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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| ssh wrote: |
Or an unexpected error in material composition (which I think it likely in this case). My point being that just because it happened doesn't mean that it's anyone's fault or that we should go looking for a scapegoat. |
Presumably (from reading the report) we're talking about a reasonably thick walled piece of steel tube (with a huge design reserve). If, as they say, it did NOT fail at a weld, then it must have had a fairly obvious problem! Tubes used in this kind of application (where the stress on the individual component is very low) do not in my experience simply fail under normal loading stress unless something is seriously wrong. Which is a good thing
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| veeeight wrote: |
| uktrailmonster, I don't doubt that things have improved over the last few years. I used to work with many a F1 engineer, when they came over to our side of the fence (OE) - they would (and still are) be amazed at the product development and validation that vehicles with a 12+ year lifecycle had to be put through, processes that are still *much* more thorough that F1. |
They are hugely different worlds. I've worked in both F1 and production car design, so I speak with personal experience. I agree that process in production car design and manufacture is more controlled, but F1 has been heading that way for a number of years now. The design parameters, materials, production methods and development timescales are all totally different. F1 is more comparable with the aerospace industry (except working to completely different design safety reserves and timescales).
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| achilles wrote: |
| petemillis, are you suggesting that forging would be more appropriate than casting? May already be done in [edit] appropriate [/edit] critical components. |
I guess so. I don't know how the component that failed in the lift was made, or even what component is was that failed. But I have had a cast brake lever clamp on my off-roady bike snap for what I though was no apparent reason, until I checked the clamp on the clutch lever and found it had been tightened way too tight.
And I've seen a problem on an engine front pulley where the centre bolt has snapped after someone had re-used the stretch bolt and repeatedly tightened every time it worked loose..
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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Things you don't want to think about while riding a lift....
I guess "poo-poo Happens" isn't a good enough explanation for the HSE though!
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| uktrailmonster wrote: |
| ssh wrote: |
Or an unexpected error in material composition (which I think it likely in this case). My point being that just because it happened doesn't mean that it's anyone's fault or that we should go looking for a scapegoat. |
Presumably (from reading the report) we're talking about a reasonably thick walled piece of steel tube (with a huge design reserve). If, as they say, it did NOT fail at a weld, then it must have had a fairly obvious problem! Tubes used in this kind of application (where the stress on the individual component is very low) do not in my experience simply fail under normal loading stress unless something is seriously wrong. Which is a good thing |
I have no doubt that water freezing in to ice could rupture steel tubes.
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You know it makes sense.
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| uktrailmonster wrote: |
| veeeight wrote: |
| uktrailmonster, I don't doubt that things have improved over the last few years. I used to work with many a F1 engineer, when they came over to our side of the fence (OE) - they would (and still are) be amazed at the product development and validation that vehicles with a 12+ year lifecycle had to be put through, processes that are still *much* more thorough that F1. |
They are hugely different worlds. I've worked in both F1 and production car design, so I speak with personal experience. I agree that process in production car design and manufacture is more controlled, but F1 has been heading that way for a number of years now. The design parameters, materials, production methods and development timescales are all totally different. F1 is more comparable with the aerospace industry (except working to completely different design safety reserves and timescales). |
Unfortunately the rules that apply to large scale mass manufacture just aren't applicable here.
These machines are all 1 offs, designed specifically for each customer. Its unlikely that any two support towers will be the same and the loads that each one will see will be different.
The type of testing that is done for something that is manufactured in the thousands is not practical. You cannot design, analyse and test every single variation from the basic design.
Yes there'll be a lot of computer analysis done at design time but that's a garbage in garbage out situation.
With equipment of this type there will be a lot of unexepected design changes made during the build and commissioning phases which doesn't tend to happen in mass production. These changes can throw up unexpected results which are usually found in the commissioning period, and sometimes not.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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or to put it another way it has more in common with the design of the plant used to manufacture a car than any similarity to designing the car itself
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Poster: A snowHead
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| petemillis wrote: |
| Why did the chair have 3 people on it whenAspen limits the number to 2? |
Designed for Europeans - operated in the US. 
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Levitt, looks might you might be closest but its not a pipe rupture.
"Preliminary inspection by B.C. safety officers has determined that this was an isolated incident of water contamination in a tower tube which caused a tower joint flange to fail due to ice-jacking," said Greg Paddon, safety manager from the B.C. Safety Authority.
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FAQ
