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--- doc:user:elements:volumes:yield_stress [2015/01/26 12:15] – joris
+++ doc:user:elements:volumes:yield_stress [2025/03/11 16:56] (current) – [SellarsTeggartYieldStress] papeleux
@@ Line 166: / Line 166: @@
 $$
-\sigma_{yield}= \sigma_0 \left( 1 + \dfrac{\dot{\overline{\varepsilon}}^{vp}}{D} \right)^{\frac{1}{p}}
+\sigma_{yield}= \sigma_0 \left( 1 + \left(\dfrac{\dot{\overline{\varepsilon}}^{vp}}{D}\right)^{\frac{1}{p}} \right)
 $$
@@ Line 298: / Line 298: @@
 |$\Theta_{0}$  |   ''KM_THETA0''       |    ''TM/TO''        |
 |${\dot{\bar{\varepsilon}}^{vp}_{0}}$ |   ''KM_DEVPL0''    |  ''-''           |
+===== SellarsTegartYieldStress =====
+Yield Stress used for hot rolling defined by  :
+  * a viscous power term :
+$$
+S0 = \sqrt{3}  \; KK (\sqrt{3}  \;\dot{\bar{\varepsilon}}^{vp})^{M0}
+$$
+  * a viscous asinh Term :
+$$
+Ss = As  \; asinh((\frac{\dot{\bar{\varepsilon}}^{vp}}{Zs})^{Ms})
+$$
+  * for the Yield Stress computed by (using a Voce hardening term):
+$$
+\sigma_{yield}  = S0 + (Ss - S0) (1-e^{-C \; \bar{\varepsilon}^{vp}})^{R}
+$$
+=== Parameters ===
+^          Name                           ^  Metafor Code  ^ Dependency         ^
+|$KK $                                     |  ''SELLARSTEGART_KK'' |  ''TM/TO''         |
+|$M0 $                                     |  ''SELLARSTEGART_M0'' |  ''TM/TO''         |
+|$As $                                     |  ''SELLARSTEGART_AS'' |  ''TM/TO''         |
+|$Zs $                                     |  ''SELLARSTEGART_MS'' |  ''TM/TO''         |
+|$Ms $                                     |  ''SELLARSTEGART_ZS'' |  ''TM/TO''         |
+|$C $                                      |  ''SELLARSTEGART_R'' |  ''TM/TO''         |
+|$R $                                      |  ''SELLARSTEGART_C'' |  ''TM/TO''         |
+===== PythonYieldStress =====
+User defined Yield Stress by a pythonDirector :
+Python Director allows user to define their own Yield Stress law. Four functions has to be defined in the Python Class : a constructor (__init__), a destructor (__del__) that must never be called, and the computation functions : getYieldStress (returning YieldStress) and getYieldHardening (returning h).
+See the example below of a Perzyna law :
+<code>
+class MyYieldStress(PythonYieldStress):
+    def __init__(self, _no, _svm0, _h, _K, _m):
+        print("MyYieldStress: __init__")
+        PythonYieldStress.__init__(self,_no)
+        self.svm0 = _svm0
+        self.h    = _h
+        self.K    = _K
+        self.m    = _m
+    def __del__(self):
+        print("MyIsoH : __del__")
+        print("callToDestructor of MyYieldStress not allowed. Add MyIsoH.__disown__()")
+        input('')
+        exit(1)
+    def getYieldStress(self, evpl, deltaEvpl, dTime, yieldGPState, pLaw):
+        #print "MyYieldStress compute Yield Stress"
+        if dTime > 0.0:
+            dEvpl = deltaEvpl/dTime
+        else:
+            dEvpl = 0.0
+        sigH = self.svm0+evpl*self.h
+        sigV = self.K*pow(dEvpl, self.m)
+        #yieldGPState.setVpStress(sigV)
+        return sigH+sigV
+    def getYieldHardening(self, epl, deltaEvpl, dTime, yieldGPState, pLaw) :
+        if dTime > 0.0:
+            dEvpl = deltaEvpl/dTime
+            h = self.h + (self.K*pow(dEvpl, self.m-1))/dTime
+        else:
+            dEvpl = 0.0
+            h = self.h
+        return h
+</code>