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 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?

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 Tue, 28 Oct 2008 12:50:22 -0700 (PDT), Chalo
wrote:

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).

[snip]

Dear Chalo,

Usually I follow you because your posts are clear to even the meanest
intelligence.

But this is a concrete example (sorry, couldn't resist it) of how even
you can overestimate the dregs of your readership.

Can you explain concrete versus wood a little more from the nail gun's
point of view?

Cheers,

Carl Fogel

Carl Fogel wrote:

Chalo wrote:

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).

[snip]

DearChalo,

Usually I follow you because your posts are clear to even the meanest
intelligence.

But this is a concrete example (sorry, couldn't resist it) of how even
you can overestimate the dregs of your readership.

Can you explain concrete versus wood a little more from the nail gun's
point of view?

Concrete is very strong in compression, but subject to being
disintegrated by shock. The shock created by a powder-fired fastener
accomplishes what a similarly large but steady axial load on the same
fastener can't, pulverizing a small zone around the nail and allowing
it to penetrate. Without the shock, a nail pushed sufficiently hard
would bend or break before penetrating the concrete enough to fasten
to it.

Wood is a resilient material and does not need to be shocked to allow
a fastener to penetrate. Thus a nail can be shot, pounded, or simply
shoved into place with comparable results in whichever case.

Chalo

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 Oct 28, 9:04*am, jim beam wrote:
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?

I have been doing lateral and radial testing on multiple wheels for
some time now using a load that increases in incriments. The load is
applied without the tire since the tire would greatly complicate
things for the simple minded such as myself. I have been wondering for
some time know if my testing is invalid since the load is not be
applied quickly like while you are riding and hit a bump. I understand
that things get very complicated when you throw a bike tire on the rim
but I was assuming that the bike tire would just allow the rim to
handle higher loads before plasticly deforming since the tire is able
to distribute the force, allowing it to be applied to a larger part to
the rim. Thus my data would be similiar to a "worse case senario"
while riding. I also found that most of the wheels I tested, with the
exception of carbon rims, could handle close to a 1000lbs or radial
load without permanantly deforming. Since I can't do the math I don't
know if this would be hard to exceed in a real world senario. But It
seems that it should be harder than it obviously is based on the
number of rims you see that have flat spots in them from excessive
radial load, especially since the rim has a tire on it to help
distribute and absorb some of the force.

Steve