Determining the coefficient of friction

In a ring compression test, a specimen 20 mm in height with outside diameter of 40 mm and inside diameter of 20 mm is reduced in thickness by 40%. Determine the coefficient of friction, m, and the friction factor, m, if the outer diameter (OD)after deformation is 50 mm.

Question

Determining the coefficient of friction

In a ring compression test, a specimen 20 mm in height with outside diameter of 40 mm and inside diameter of 20 mm is reduced in thickness by 40%. Determine the coefficient of friction, m, and the friction factor, m, if the outer diameter (OD)after deformation is 50 mm.

Accepted Answer

We first have to determine the new inner diameter (ID); this diameter is obtained from volume constancy, as follows:

[latex] ext { Volume }=\frac{\pi}{4}\left(40^{2}-20^{2} ight) 20=\frac{\pi}{4}\left(50^{2}-\mathrm{ID}^{2} ight) 12[/latex]

From this equation, we find that the new ID=22.36 mm. Thus,

Change in ID=[latex]\frac{20-22.36}{20} imes 100 \%=-11.8 \%[/latex](increase).

For a 40% reduction in height and a 11.8% reduction in ID, the following values are interpolated from Fig. 4.8:

μ=0.03 and m=0.11.

Question 4.1: Determining the coefficient of friction In a ring compressio...

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