Do you have a clear design criteria for the friction
load?
- Christopher Wright <chrisw@skypoint.com> wrote:
> >I am using 0.3 as a friction coef. It is for the
> >sliding friction.
> How do you know that the friction force really is
> 30% of the normal
> force? Do you have measurements?
>
> I'm really not just being a smart-ass. The real
> coefficient varies all
> over the place. For example, I've seen values for
> stainless on stainless
> taken from an exhaustive series of tests which range
> from 0.2 to 0.8.
> Marks Handbook lists 0.7 as the static coefficient
> for steel on steel,
> but it applies to laboratory clean and polished
> surfaces in vacuum. I've
> measured values on machined surfaces that's closer
> to 0.3 Harris and
> Crede show 0.15 for sliding friction for steel on
> steel. The values
> depend on surface condition, the presence of any
> liquid and speed for
> sliding friction. And contrary to the CW, the value
> does vary with
> surface pressure, although it's constant for
> ordinary pressures.
>
> That's actually tangential to the original question
> of whether or not to
> ignore friction, but it is germane to how much faith
> you can have in the
> results of an assessment. Don't forget that both the
> high and the low
> values may produce non-conservative results. High
> values produce
> non-conservative displacments and conservative
> forces.
>
> Christopher Wright P.E. |"They couldn't hit an
> elephant at
> chrisw@skypoint.com | this distance" (last
> words of Gen.
> ___________________________| John Sedgwick,
> Spotsylvania 1864)
> <a href="http://www.skypoint.com/~chrisw">http://www.skypoint.com/~chrisw</a>
>
>
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Best Regards
(:- Itzhak Shdemati -:)
Received on Wed Apr 23 15:21:00 2003