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Science Forum Index » Mechanics Forum » which friction coefficient to apply ?
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| Guest |
 Posted: Tue Apr 29, 2008 9:06 pm |
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Hello,
If looking up a friction coefficient in friction tables, they vary
sometimes, or a friction interval is given.
So, I am wondering which friction coefficient I have to apply ? Are
there any rules of thumb therefore ? Should I take an average or ...
friendly greetings |
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| Guest |
| Posted: Wed Apr 30, 2008 6:19 am |
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On Apr 30, 3:06 am, de.bruy...@gmail.com wrote:
Quote: Hello,
If looking up a friction coefficient in friction tables, they vary
sometimes, or a friction interval is given.
So, I am wondering which friction coefficient I have to apply ? Are
there any rules of thumb therefore ? Should I take an average or ...
friendly greetings
When I started my career a wise senior design engineer told me to
never count on friction to help you and always assume it will hurt
you. In other words, never use the average friction values, use the
min or max depending which is most conservative for the problem you
are working on. For example, in designing a bolted joint, use the max
friction value to determine the minimum pre-load for a given bolt
torque. Then use the min friction to determine the maximum tensile
stress in the bolt at the same torque. If you can't live with both
extremes redesign the joint.
Dave |
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| N:dlzc D:aol T:com (dlzc) |
| Posted: Wed Apr 30, 2008 8:18 am |
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Guest
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Dear de.bruyn.b:
<de.bruyn.b@gmail.com> wrote in message
news:f23d6d0f-4666-4612-988c-3f7502364031@m36g2000hse.googlegroups.com...
....
Quote: If looking up a friction coefficient in friction tables,
they vary sometimes, or a friction interval is given.
So, I am wondering which friction coefficient I
have to apply ? Are there any rules of thumb
therefore ? Should I take an average or ...
If you need a typical value, say for a homework assignment, take
the average.
If a surface is being freshly used for "braking" use the higher
value, wearing into the lower value.
If it is a life-critical application take the value that will
cause the most harm.
They are empirical relations, established by Nature, without
anything in the way of theoretical support. She likes wiggle
room.
David A. Smith |
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| Brian Whatcott |
| Posted: Wed Apr 30, 2008 7:26 pm |
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Guest
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On Wed, 30 Apr 2008 00:06:52 -0700 (PDT), de.bruyn.b@gmail.com wrote:
Quote: Hello,
If looking up a friction coefficient in friction tables, they vary
sometimes, or a friction interval is given.
So, I am wondering which friction coefficient I have to apply ? Are
there any rules of thumb therefore ? Should I take an average or ...
friendly greetings
Friction varies. It would be well to take the coefficient most adverse
to the purpose, then apply a design factor in the usual way.
Brian W |
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