Friction Calculation for Two Different types of materials 3

• Oct 8, 2015

1
• #2

3DDave

Aerospace

May 23, 2013

11,451

US

Typically the friction coefficient is not calculated; it is measured in testing. The same is true for almost all physical properties of materials.

 

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• Oct 8, 2015

• #3

gruntguru

Mechanical

Mar 1, 2008

1,279

AU

I assume the OP has found a coefficient for each material (sliding like on like) and is asking if there is a method to calculate the coefficient for the dissimilar pair from that knowledge.

(The answer of course is "no")

je suis charlie

 

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• Oct 8, 2015

• #4

swertel

Mechanical

Dec 21, 2000

2,067

US

A very simple test.

Grab a sample of whatever material you need to test the friction coefficient.
Weigh it.
Put it on the mating material you want to measure the friction coefficient between.
Tilt the base until the sample material begins to slide.
Measure the angle.

F_f = Coeff * F_N

Based on the angle you measured, and the weight (aka force) of your sample, you can calculate the component forces. The only variable left in the equation is the coefficient of sliding friction.

--Scott
www.wertel.pro

 

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• Oct 8, 2015

• #5

dgallup

Automotive

May 9, 2003

4,715

US

Better test a large number of samples, there will be lots of variation.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

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• Oct 8, 2015

• #6

btrueblood

Mechanical

May 26, 2004

10,033

US

Wondering what "cotton box" is...unless it's just a box of cotton.

 

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• Oct 8, 2015

1
• #7

Tmoose

Mechanical

Apr 12, 2003

5,636

US

Some materials' friction coefficients are pretty sensitive to unit loading.

An extreme example is some stainless steels on each other.
Tables XI and XII here -

http://www.nickelinstitute.org/~/Me...lingCharacteristicsofStainlessSteel_9006_.pdf

 

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• Oct 8, 2015

• #8

gruntguru

Mechanical

Mar 1, 2008

1,279

AU

Swertel. Nice test but - that will give static friction coeff. OP wants kinetic.

je suis charlie

 

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• Oct 8, 2015

• Thread starter
• #9

Johndesign123

Mechanical

Apr 7, 2015

14

TH

Btrueblood,

That's not a empty Cotton box.It have coffee Bag.It would be around 10 kg weight.

 

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• Oct 8, 2015

• Thread starter
• #10

Johndesign123

Mechanical

Apr 7, 2015

14

TH

Thank you very Much for yours valuable reply.

 

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• Oct 9, 2015

• #11

swertel

Mechanical

Dec 21, 2000

2,067

US

Gruntguru,

You are correct. I was thinking about this after I posted that the test isn't totally complete.

Get a much bigger piece of base material. After it starts sliding, decrease the angle until it stops sliding. That will give you the coefficient of kinetic (sliding) friction instead of static friction.

And absolutely take a lot of samples!

--Scott
www.wertel.pro

 

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• Oct 9, 2015

1
• #12

tbuelna

Aerospace

Aug 10, 2002

4,026

US

Tmoose makes an excellent point about sensitivity to unit loading with the friction coefficient of a woven textile substrate made from natural fibers. When new the textile's cotton fibers will have a certain surface texture. But after being compressed and dragged over PVC a bit, their surface texture will change and this will likely affect both the static and dynamic coefficients of friction. So to get a useful set of test data, you'd need to test a number of identical specimens under the same conditions for several combinations of unit loading, operating cycles, etc. The setup to perform this testing is not complicated or expensive, but it will require a fair amount of your time to complete.

I think what you'll find is that over time the cotton textile material repeatedly sliding over the PVC will polish its surface and reduce both the static and dynamic friction coefficients at the contact interface. The same thing occurs with many other sliding contacts, where the friction coefficients drop as the parts "break in". This is something you may need to take into account with your design.

 

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