surface roughness effect on tensile strength

[Tmoose]

I'm used to using the surface condition to de-rate both the tensile strength and endurance limit of various steel materials.

I know of a company that applies the full published tensile strength and endurance limit to the FEA stress results. I see how FEA solves for the "real" stress concentration factor, but.......

 

[metengr]

Tmoose;
How do you derate, or better yet, use a reduction factor for tensile strength for surface roughness? I fully understand applying a reduction factor for endurance limit related to fatigue crack initiation and propagation.

Tensile strength is a determined value that measures the rupture or breaking strength of a material and does not vary with surface roughness. I can see applying a stress reduction factor for a statically applied tensile stress to account for local stress concentration at the surface, if this is what you mean by derating. Once the applied service stress reaches the measured tensile strength you have rupture of the material.

 

[damienk]

tensile strength depends only of cold working which could be associated to the surface preparation and undirectely caractersed by roughness. But roughness alone does not mean anything.

 

[Tmoose]

So, everyone DOES consider a part's surface condition (not meant to be construed as surface finish or roughness) when establishing a material's endurance limit?

 

[metengr]

Yes.