Wheel deflection

Does anybody know if a rim would react differently to a sudden load
versus a gradual load? What I mean is if you were to apply a gradual
load on a wheel would that rim be able to handle a higher load before
permanantly deforming than if you were to apply the same load very
quickly?

Steve

Steve Sauter wrote:

Does anybody know if a rim would react differently to a sudden load
versus a gradual load? What I mean is if you were to apply a
gradual load on a wheel would that rim be able to handle a higher
load before permanently deforming than if you were to apply the same
load very quickly?

Time of loading has no effect on metals that see no difference between
acoustic frequencies and long slow loading. The only difference is
that sharp impact often has higher forces than is apparent to human
observation. That observation is colored by the time dependence of
human tissue that receives damage from fluid displacement. Typically
slamming ones fist on a hard surface can withstand far greater force
than squeezing the fist in a vise.

What sort of loading did you have in mind? Don't overlook that a rim
is cushioned by a pneumatic tire that absorbs peak forces and passes
them on greatly reduced. That's what pneumatic and mechanical springs
are supposed to do.

Jobst Brandt

On Tue, 28 Oct 2008 05:20:26 +0000, jobst.brandt wrote:

Steve Sauter wrote:

Does anybody know if a rim would react differently to a sudden load
versus a gradual load? What I mean is if you were to apply a gradual
load on a wheel would that rim be able to handle a higher load before
permanently deforming than if you were to apply the same load very
quickly?

Time of loading has no effect on metals

untrue. many materials react differently depending on loading rate. for
example, this is why you have nail guns - they succeed at a high rate on
driving nails into concrete whereas trying to do the same job at a lower
rate always fails. the deep drawing process used on stainless kitchenware
is usually done at high rates also because at low rates, the material does
not exhibit sufficient ductility.

so, the question now is, at what /rate/ will the o.p. experience a
difference?


that see no difference between
acoustic frequencies and long slow loading. The only difference is that
sharp impact often has higher forces than is apparent to human
observation. That observation is colored by the time dependence of
human tissue that receives damage from fluid displacement. Typically
slamming ones fist on a hard surface can withstand far greater force
than squeezing the fist in a vise.

typical unquantified suppositional jobstian b.s.




What sort of loading did you have in mind? Don't overlook that a rim is
cushioned by a pneumatic tire that absorbs peak forces and passes them
on greatly reduced.

action = reaction jobst. it's impossible, in newtonian physics at any
rate, for any load exerted on a tire to not be transmitted to its rim, and
thus the wheel, fork, rider, etc.

That's what pneumatic and mechanical springs are
supposed to do.

so factor time into the equation then, don't mis-state the fundamentals!!!

On Mon, 27 Oct 2008 21:08:19 -0700, steve wrote:

Does anybody know if a rim would react differently to a sudden load
versus a gradual load? What I mean is if you were to apply a gradual
load on a wheel would that rim be able to handle a higher load before
permanantly deforming than if you were to apply the same load very
quickly?


for the same load magnitude, strictly speaking, it depends on the rate.
in typical riding situations, you'll see no difference, only at very high
loading rates.

why?

On Tue, 28 Oct 2008 08:01:54 -0500, jim beam wrote:

On Tue, 28 Oct 2008 05:20:26 +0000, jobst.brandt wrote:

Steve Sauter wrote:

Does anybody know if a rim would react differently to a sudden load
versus a gradual load? What I mean is if you were to apply a gradual
load on a wheel would that rim be able to handle a higher load before
permanently deforming than if you were to apply the same load very
quickly?

Time of loading has no effect on metals

untrue. many materials react differently depending on loading rate. for
example, this is why you have nail guns - they succeed at a high rate on
driving nails into concrete

So, "jim beam" - concrete is a metal now, is it?

steve wrote:
Does anybody know if a rim would react differently to a sudden load
versus a gradual load? What I mean is if you were to apply a gradual
load on a wheel would that rim be able to handle a higher load before
permanantly deforming than if you were to apply the same load very
quickly?

With suddenly applied loads, there's an inertia effect that generally
makes things worse.

The classic example is gently placing a load on a spring, vs. suddenly
releasing the same load onto the same spring. Even if the load is
(barely) touching the spring just before it's released, the spring
momentarily deflects twice as far as with the gently placed load, and
the peak force on the spring is twice as great.

If the load were applied by a mechanism that didn't involve mass and
inertia, I don't believe that effect would be present. But bike wheel
loads do involve mass and inertia.

- Frank Krygowski

Frank Krygowski wrote:

Does anybody know if a rim would react differently to a sudden load
versus a gradual load? What I mean is if you were to apply a
gradual load on a wheel would that rim be able to handle a higher
load before permanantly deforming than if you were to apply the
same load very quickly?

With suddenly applied loads, there's an inertia effect that
generally makes things worse.

Let's not leave it at such a vague description. The question is load,
regardless of its origin, inertial or dead weight. The rate of stress
application has no effect on metals, at least up to acoustic
frequencies.

The classic example is gently placing a load on a spring, vs. suddenly
releasing the same load onto the same spring. Even if the load is
(barely) touching the spring just before it's released, the spring
momentarily deflects twice as far as with the gently placed load, and
the peak force on the spring is twice as great.

Those are two different loads. The question was about load
application and possibly duration causing plastic deformation.

If the load were applied by a mechanism that didn't involve mass and
inertia, I don't believe that effect would be present. But bike wheel
loads do involve mass and inertia.

Bicycle wheels do not involve mass AND inertia. Loads are mainly
rider and bicycle mass and their inertia. The mass of the wheel and
tire is insignificant in that respect. An example of that would be to
toss a wheel, with inflated tire, into the air and watch it bounce
undamaged on pavement. To damage a wheel in that manner would take a
hefty toss, especially with a fat (2+ tire) inch.

Jobst Brandt

On Oct 28, 8:01*am, jim beam wrote:
On Tue, 28 Oct 2008 05:20:26 +0000, jobst.brandt wrote:
Steve Sauter wrote:

Does anybody know if a rim would react differently to a sudden load
versus a gradual load? *What I mean is if you were to apply a gradual
load on a wheel would that rim be able to handle a higher load before
permanently deforming than if you were to apply the same load very
quickly?

Time of loading has no effect on metals

untrue. *many materials react differently depending on loading rate. *for
example, this is why you have nail guns - they succeed at a high rate on
driving nails into concrete whereas trying to do the same job at a lower
rate always fails. *the deep drawing process used on stainless kitchenware
is usually done at high rates also because at low rates, the material does
not exhibit sufficient ductility.

so, the question now is, at what /rate/ will the o.p. experience a
difference?

that see no difference between
acoustic frequencies and long slow loading. *The only difference is that
sharp impact often has higher forces than is apparent to human
observation. *That observation is colored by the time dependence of
human tissue that receives damage from fluid displacement. *Typically
slamming ones fist on a hard surface can withstand far greater force
than squeezing the fist in a vise.

typical unquantified suppositional jobstian b.s.



What sort of loading did you have in mind? *Don't overlook that a rim is
cushioned by a pneumatic tire that absorbs peak forces and passes them
on greatly reduced.

action = reaction jobst. *it's impossible, in newtonian physics at any
rate, for any load exerted on a tire to not be transmitted to its rim, and
thus the wheel, fork, rider, etc.

That's what pneumatic and mechanical springs are
supposed to do.

so factor time into the equation then, don't mis-state the fundamentals!!!

jim beam wrote:

Jobst Brandt wrote:

Time of loading has no effect on metals

untrue. *many materials react differently depending on loading rate. *for
example, this is why you have nail guns - they succeed at a high rate on
driving nails into concrete whereas trying to do the same job at a lower
rate always fails. *

Concrete is the issue. Whack a nail into wood, or push it in with an
arbor press, and it's about the same (although the whacked nail might
hold better due to local heating of the wood resins).

Don't overlook that a rim is
cushioned by a pneumatic tire that absorbs peak forces and passes them
on greatly reduced.

action = reaction jobst. *it's impossible, in newtonian physics at any
rate, for any load exerted on a tire to not be transmitted to its rim, and
thus the wheel, fork, rider, etc.

What part of "peak forces" don't you get? Try running your bike
without a tire (I have) and see how long it takes for your butt to
throw in the towel.

http://www.morrispost.com/rimridep.htm

Chalo

On Oct 28, 1:25*pm, wrote:
Frank Krygowski wrote:
Does anybody know if a rim would react differently to a sudden load
versus a gradual load? *What I mean is if you were to apply a
gradual load on a wheel would that rim be able to handle a higher
load before permanantly deforming than if you were to apply the
same load very quickly?
With suddenly applied loads, there's an inertia effect that
generally makes things worse.

Let's not leave it at such a vague description. *The question is load,
regardless of its origin, inertial or dead weight. *The rate of stress
application has no effect on metals, at least up to acoustic
frequencies.

That depends on exactly what Steve meant by "load."

The classic example is gently placing a load on a spring, vs. suddenly
releasing the same load onto the same spring. *Even if the load is
(barely) touching the spring just before it's released, the spring
momentarily deflects twice as far as with the gently placed load, and
the peak force on the spring is twice as great.

Those are two different loads. *The question was about load
application and possibly duration causing plastic deformation.

If Steve could tell us more about exactly what he means, we could
determine whether the sudden application of an object onto a spring is
properly analogous. I believe it's likely, but he's given no details.

If the load were applied by a mechanism that didn't involve mass and
inertia, I don't believe that effect would be present. *But bike wheel
loads do involve mass and inertia.

Bicycle wheels do not involve mass AND inertia. *Loads are mainly
rider and bicycle mass and their inertia. *The mass of the wheel and
tire is insignificant in that respect. *An example of that would be to
toss a wheel, with inflated tire, into the air and watch it bounce
undamaged on pavement. *To damage a wheel in that manner would take a
hefty toss, especially with a fat (2+ tire) inch.

Bicycle wheels support mass. That mass has inertia. It makes a
difference.

Example: A 200 pound bike+rider sitting still on level ground causes
certain stresses in the various wheel components. That same bike
+rider dropping one foot down onto level ground causes much more
stress. If Steve was envisioning anything similar, the fact that
wheel masses are low has no bearing.

So, Steve, what do you have in mind?

- Frank Krygowski