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Surface_Factor

Surface_factor(S_ut,Finish$)

Function Surface_factor returns the endurance limit modification factor associated with surface finish (The Marin factor k_a)

Inputs:

S_ut - ultimate tensile strength ([MPa] or [ksi])

Finish$ - string indicating the surface finish:

 'Polished' for polished finish

 'Ground' for ground finish

 'Machined' or 'Cold_drawn' for machined or cold drawn finish

 'Hot_rolled' for hot rolled finish

 'As_forged' for as forged finish

Output:

Returns the dimensionless endurance limit modification factor associated with surface finish.

Example:  

$UnitSystem SI Mass J K Pa

S_ut=1000 [MPa]

Finish$='As_forged'

k_a=Surface_Factor(S_ut,Finish$)

{Solution:

k_a = 0.2921}

Reference:  Budynas, R.G. and J. Keith Nisbett, Shigley's Mechanical Engineering Design, 11th Edition, McGraw Hill, New York, (2020).

The function uses the curve fit parameters found in Table 6-2.  For low values of S_ut where k_a>1 the function limits k_a to 1.

Endurance Limits