calculating shear strain from max principal strain and min principal strain

ivolResults.002.py

    # tensors for loading and unloading frame of cycle
    loadFieldLE = odb.steps[lastStepName].frames[0].fieldOutputs['LE']
    loadFieldS = odb.steps[lastStepName].frames[0].fieldOutputs['S']
    unloadFieldLE = odb.steps[lastStepName].frames[-1].fieldOutputs['LE']
    unloadFieldS = odb.steps[lastStepName].frames[-1].fieldOutputs['S']

    # calculate tensor mean and amplitude values
    meanLE = 0.5*(loadFieldLE+unloadFieldLE)
    ampLE = 0.5*(loadFieldLE-unloadFieldLE)
    meanS = 0.5*(loadFieldS+unloadFieldS)
    ampS = 0.5*(loadFieldS-unloadFieldS)

    # loading max and min principal strains, shear
    ldE1 = []
    ldE3 = []
    ldTau = []
    for v in loadFieldLE.values:
        minPrincipalStrain = v.minPrincipal
        maxPrincipalStrain = v.maxPrincipal
        maxTau = abs(maxPrincipalStrain - minPrincipalStrain)/2
        ldE1.append(v.minPrincipal)
        ldE3.append(v.maxPrincipal)
        ldTau.append(maxTau)    
        
    # unloading max and min principal strains, shear
    ulE1 = []
    ulE3 = []
    ulTau = []
    for v in unloadFieldLE.values:
        minPrincipalStrain = v.minPrincipal
        maxPrincipalStrain = v.maxPrincipal
        maxTau = abs(maxPrincipalStrain - minPrincipalStrain)/2
        ulE1.append(v.minPrincipal)
        ulE3.append(v.maxPrincipal)
        ulTau.append(maxTau)    

    # cyclic strain amplitude, and update maxumum strain amplitude
    cycEA = []
    for v in ampLE.values:
        cycE3 = v.maxPrincipal
        cycE1 = v.minPrincipal
        if abs(cycE3) > abs(cycE1):
            cycE3abs = cycE3
        else:
            cycE3abs = cycE1
        cycEA.append(cycE3abs)
        if abs(cycE3abs) > abs(cycEAmax):
            cycEAmax = cycE3abs
            
    # cyclic shear strain
    cycTau = []
    for v in ampLE.values:
        cycE3 = v.maxPrincipal
        cycE1 = v.minPrincipal
        tau = abs(cycE3 - cycE1)/2
        cycTau.append(tau)