Differential Yield Stress and Von Mises Criterion

[1350-F]

If I have the differential yield stress σ_d=(σ₁-σ₃) for a material, what can I derive from that for use with the von mises criterion? Do I have k=0.5×(σ₁-σ₃) or σ_y in axial tension, where σ₃ = 0? Essentially is my axial yield stress = σ_d or √3 × σ_d /2? (in plane stress)

 

[Chestermiller]

See this: http://en.wikipedia.org/wiki/Von_Mises_yield_criterion

 

[1350-F]

See this: http://en.wikipedia.org/wiki/Von_Mises_yield_criterion

Reading this confirmed my suspicions that the axial yield would equal the differential yield and from there you would divide by √3 to get k. For tresca k would equal σ_d/2. In that case why report it as a differential stress? I think that's what was throwing me off. Assuming we would know to add the axial yield to any hydrostatic stress to get our maximum principal stress why give σd?

 

[Chestermiller]

Reading this confirmed my suspicions that the axial yield would equal the differential yield and from there you would divide by √3 to get k. For tresca k would equal σ_d/2. In that case why report it as a differential stress? I think that's what was throwing me off. Assuming we would know to add the axial yield to any hydrostatic stress to get our maximum principal stress why give σd?

The reason differential stress is used is that people out-of-the-know can relate to it easily.

Chet