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FEM: result tools, von mises, use a simplified calculation formula

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Bernd Hahnebach
2019-03-25 07:52:27 +01:00
committed by wmayer
parent 4da61569ce
commit c511ecc7f7
1 changed files with 8 additions and 14 deletions
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22
src/Mod/Fem/femresult/resulttools.py
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@@ -30,6 +30,7 @@ __url__ = "http://www.freecadweb.org"
import FreeCAD
import femtools.femutils as femutils
from math import pow, sqrt
import numpy as np
## Removes all result objects and result meshes from an analysis group
@@ -332,23 +333,16 @@ def compact_result(res_obj):
def calculate_von_mises(stresstuple):
# Von mises stress (http://en.wikipedia.org/wiki/Von_Mises_yield_criterion)
s11 = stresstuple[0] # Sxx
s22 = stresstuple[1] # Syy
s33 = stresstuple[2] # Szz
s12 = stresstuple[3] # Sxy
s31 = stresstuple[4] # Sxz
s23 = stresstuple[5] # Syz
s11s22 = pow(s11 - s22, 2)
s22s33 = pow(s22 - s33, 2)
s33s11 = pow(s33 - s11, 2)
s12s23s31 = 6 * (pow(s12, 2) + pow(s23, 2) + pow(s31, 2))
vm_stress = sqrt(0.5 * (s11s22 + s22s33 + s33s11 + s12s23s31))
return vm_stress
# Von mises stress: http://en.wikipedia.org/wiki/Von_Mises_yield_criterion
# simplification: https://forum.freecadweb.org/viewtopic.php?f=18&t=33974&p=296542#p296542
# stresstuple ... (Sxx, Syy, Szz, Sxy, Sxz, Syz)
normal = stresstuple[:3]
shear = stresstuple[3:]
pressure = np.average(normal)
return np.sqrt(1.5 * np.linalg.norm(normal - pressure)**2 + 3.0 * np.linalg.norm(shear)**2)
def calculate_principal_stress(stresstuple):
import numpy as np
s11 = stresstuple[0] # Sxx
s22 = stresstuple[1] # Syy
s33 = stresstuple[2] # Szz