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- 1970-1-1
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发表于 2009-1-1 15:03:31
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来自 加拿大
The option of “Max. Principal stress" is somewhat misleading from the name. It actually is not what the name means. Say you have a time history like the following% {: @' Q2 G' t. }1 Y) `
# d: B7 _2 J0 w+ J2 [. u2 z NTime 0 1 2 3 4 Max. Range# A2 H9 D- ?4 T$ x3 i4 B1 b- ]7 L
Max. Principal 100 -100 200 -200 500 -200~500 = 700
( X5 N! A) P; O- d5 KMin. Principal 50 -150 -500 -250 -10 -500~ 50 = 550
( Z! r& l# Q& n. LAbs Max. Principal 100 -150 -500 -250 500 -500~500=1000
6 \) E* T) F) k: L* C5 R; u+ c) C& S, A) i! `, U% x# b9 Y0 @& s9 j" I
What is the catch here?. {2 J# n! k# q& ]
Using Abs Max. Principal stress actually gives a larger stress range than using Max or Min. Principal. The ABS doesn’t mean to take away the sign. What it does is to take the largest absolute value and leave the sign.
3 J* Z9 ]3 R) M, S5 T+ C' QBut how about the von Mises or Shear/Tresca? These values tend to be always positive which halves the actual stress range. / o: ^; @4 \$ _9 e
If you prefer to use von Mises stress, then use signed von Mises instead. The Abs. Max. Principal is a more conservative option. Basically, the Abs. Max. Principal is suitable for fatigue calculation though it yield more severe result. After all, von Mises is a non –directional scalar while fatigue cracks are directional. # @( E" N* ]! J/ b' N6 t
However, from my personal experience, signed von Mises sometimes correlate much better with test result compared to Abs, max. principal. |
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