Von mises smaller than tresca in calculations

[kookie]

hi every one.
i am struggling with the same problem. my principal stresses were the same as the guys above but my von mises σyeild=325MPa which is also smaller than the tresca hexagon σyield =421 MPa.
von mises = σ1^2+σ2^2-σ1σ2=(σyield/K)^2

i was wandering if this method was correct

p.s. is there a reason behind why vonmises's is nearly 100MPa lesser than tresca

 

[Mapes]

hi every one.
i am struggling with the same problem. my principal stresses were the same as the guys above but my von mises σyeild=325MPa which is also smaller than the tresca hexagon σyield =421 MPa.
von mises = σ1^2+σ2^2-σ1σ2=(σyield/K)^2

i was wandering if this method was correct

p.s. is there a reason behind why vonmises's is nearly 100MPa lesser than tresca

Hi kookie, welcome to PF!

Please give the entire problem and your entire solution, and then you'll likely get useful comments. Nobody can know how you set up and performed the calculations otherwise.

 

[russs91]

I am also struggling on the same problem.

I have the tresca yield value as 421
and the von Mises value as 365

When i draw the loci it makes the von Mises elipse fit exactly inside the Tresca

bit confused

 

[kookie]

hey guys i found out through my lecturer that in that specific case it would be appropriate to draw two separate locis one for von mises and one for tresca and analyse the on them stresses separately.

Good luck

 

[nvn]

I assume posts 1 and 3 refer to post https://www.physicsforums.com/showthread.php?t=449446#post2996853". Please correct me if I am wrong.

PS: Is there a reason why von Mises stress is nearly 100 MPa less than tresca?

kookie: Yes. The reason is because you made a mistake. Tresca stress is never greater than 15.5 % greater than von Mises stress, as in post 3. See post 2 by Mapes.

When I draw the loci, it makes the von Mises ellipse fit exactly inside the Tresca.

russs91: The maximum shear stress theory (Tresca) failure envelope (locus, hexagon) always fits inside the von Mises ellipse. Therefore, it appears you have something amiss. See post 2 by Mapes.