Failure criteria

[EngForm78]

I am trying to predict failure for a cast zinc material. I look at the contour plots which give me mises stresses. But, how do I know if I am outside the failure surface? Also, I have Abaqus/explict so this may be my limitation. Any reccomendations on how to choose a failure criteria for FEA problems.

Thanks in advance

EngForm78

 

[corus]

It's not a failure criteria for FEA but for structures in general. You should look at failure beyond yield, fracture and fatigue, buckling, incremental collapse, and creep damage if you want modes of failure.

corus

 

[Drej]

> I look at the contour plots which give me mises stresses. But, how do I know if I am outside the failure surface?

Well, why are you looking at Mises stress?

 

[EngForm78]

Thanks for the replies

At this point I am considering any yield as failure, so elemental failure will occur at a mises stress > yield stress.

What I was trying to do is verify how FEA mises stresses are calculated in a state of pure shear. I have fiugred this as follows and I think its O.K.

If I subject a round bar to a certain torque T the shear stress should be t(tau)=T*c/J. If only a torque is applied to the end, the bar is in pure shear and my max and min principal stresses; sigma,a and sigma,b are equal to +/- t(tau). Now I can calculate my mises stress as (sigma,a)^2 -(sigma,a)*(sigma,b)+(sigma,b)^2=(sigma,mises)^2.

Thanks

EngForm78