DAMASK_EICMD/python/damask/mechanics.py

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"""
Finite-strain continuum mechanics.
All routines operate on numpy.ndarrays of shape (...,3,3).
"""
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from . import tensor as _tensor
from . import _rotation
import numpy as _np
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def deformation_Cauchy_Green_left(F):
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"""
Calculate left Cauchy-Green deformation tensor (Finger deformation tensor).
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Parameters
----------
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F : numpy.ndarray of shape (...,3,3)
Deformation gradient.
Returns
-------
B : numpy.ndarray of shape (...,3,3)
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Left Cauchy-Green deformation tensor.
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"""
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return _np.matmul(F,_tensor.transpose(F))
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def deformation_Cauchy_Green_right(F):
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"""
Calculate right Cauchy-Green deformation tensor.
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Parameters
----------
F : numpy.ndarray of shape (...,3,3)
Deformation gradient.
Returns
-------
C : numpy.ndarray of shape (...,3,3)
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Right Cauchy-Green deformation tensor.
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"""
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return _np.matmul(_tensor.transpose(F),F)
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def equivalent_strain_Mises(epsilon):
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"""
Calculate the Mises equivalent of a strain tensor.
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Parameters
----------
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epsilon : numpy.ndarray of shape (...,3,3)
Symmetric strain tensor of which the von Mises equivalent is computed.
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Returns
-------
epsilon_vM : numpy.ndarray of shape (...)
Von Mises equivalent strain of epsilon.
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"""
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return _equivalent_Mises(epsilon,2.0/3.0)
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def equivalent_stress_Mises(sigma):
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"""
Calculate the Mises equivalent of a stress tensor.
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Parameters
----------
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sigma : numpy.ndarray of shape (...,3,3)
Symmetric stress tensor of which the von Mises equivalent is computed.
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Returns
-------
sigma_vM : numpy.ndarray of shape (...)
Von Mises equivalent stress of sigma.
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"""
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return _equivalent_Mises(sigma,3.0/2.0)
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def maximum_shear(T_sym):
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"""
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Calculate the maximum shear component of a symmetric tensor.
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Parameters
----------
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T_sym : numpy.ndarray of shape (...,3,3)
Symmetric tensor of which the maximum shear is computed.
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Returns
-------
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gamma_max : numpy.ndarray of shape (...)
Maximum shear of T_sym.
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"""
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w = _tensor.eigenvalues(T_sym)
return (w[...,0] - w[...,2])*0.5
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def rotation(T):
"""
Calculate the rotational part of a tensor.
Parameters
----------
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T : numpy.ndarray of shape (...,3,3)
Tensor of which the rotational part is computed.
Returns
-------
R : damask.Rotation of shape (...)
Rotational part of the vector.
"""
return _rotation.Rotation.from_matrix(_polar_decomposition(T,'R')[0])
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def strain(F,t,m):
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"""
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Calculate strain tensor (SethHill family).
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For details refer to https://en.wikipedia.org/wiki/Finite_strain_theory and
https://de.wikipedia.org/wiki/Verzerrungstensor
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Parameters
----------
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F : numpy.ndarray of shape (...,3,3)
Deformation gradient.
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t : {V, U}
Type of the polar decomposition, V for left stretch tensor
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and U for right stretch tensor.
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m : float
Order of the strain.
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Returns
-------
epsilon : numpy.ndarray of shape (...,3,3)
Strain of F.
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"""
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if t == 'V':
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w,n = _np.linalg.eigh(deformation_Cauchy_Green_left(F))
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elif t == 'U':
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w,n = _np.linalg.eigh(deformation_Cauchy_Green_right(F))
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if m > 0.0:
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eps = 1.0/(2.0*abs(m)) * (+ _np.einsum('...j,...kj,...lj',w**m,n,n) - _np.eye(3))
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elif m < 0.0:
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eps = 1.0/(2.0*abs(m)) * (- _np.einsum('...j,...kj,...lj',w**m,n,n) + _np.eye(3))
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else:
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eps = _np.einsum('...j,...kj,...lj',0.5*_np.log(w),n,n)
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return eps
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def stress_Cauchy(P,F):
"""
Calculate the Cauchy stress (true stress).
Resulting tensor is symmetrized as the Cauchy stress needs to be symmetric.
Parameters
----------
P : numpy.ndarray of shape (...,3,3)
First Piola-Kirchhoff stress.
F : numpy.ndarray of shape (...,3,3)
Deformation gradient.
Returns
-------
sigma : numpy.ndarray of shape (...,3,3)
Cauchy stress.
"""
return _tensor.symmetric(_np.einsum('...,...ij,...kj',1.0/_np.linalg.det(F),P,F))
def stress_second_Piola_Kirchhoff(P,F):
"""
Calculate the second Piola-Kirchhoff stress.
Resulting tensor is symmetrized as the second Piola-Kirchhoff stress
needs to be symmetric.
Parameters
----------
P : numpy.ndarray of shape (...,3,3)
First Piola-Kirchhoff stress.
F : numpy.ndarray of shape (...,3,3)
Deformation gradient.
Returns
-------
S : numpy.ndarray of shape (...,3,3)
Second Piola-Kirchhoff stress.
"""
return _tensor.symmetric(_np.einsum('...ij,...jk',_np.linalg.inv(F),P))
def stretch_left(T):
"""
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Calculate left stretch of a tensor.
Parameters
----------
T : numpy.ndarray of shape (...,3,3)
Tensor of which the left stretch is computed.
Returns
-------
V : numpy.ndarray of shape (...,3,3)
Left stretch tensor from Polar decomposition of T.
"""
return _polar_decomposition(T,'V')[0]
def stretch_right(T):
"""
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Calculate right stretch of a tensor.
Parameters
----------
T : numpy.ndarray of shape (...,3,3)
Tensor of which the right stretch is computed.
Returns
-------
U : numpy.ndarray of shape (...,3,3)
Left stretch tensor from Polar decomposition of T.
"""
return _polar_decomposition(T,'U')[0]
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def _polar_decomposition(T,requested):
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"""
Perform singular value decomposition.
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Parameters
----------
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T : numpy.ndarray of shape (...,3,3)
Tensor of which the singular values are computed.
requested : iterable of str
Requested outputs: R for the rotation tensor,
V for left stretch tensor and U for right stretch tensor.
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"""
u, _, vh = _np.linalg.svd(T)
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R = _np.einsum('...ij,...jk',u,vh)
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output = []
if 'R' in requested:
output.append(R)
if 'V' in requested:
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output.append(_np.einsum('...ij,...kj',T,R))
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if 'U' in requested:
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output.append(_np.einsum('...ji,...jk',R,T))
if len(output) == 0:
raise ValueError('output needs to be out of V, R, U')
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return tuple(output)
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def _equivalent_Mises(T_sym,s):
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"""
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Base equation for Mises equivalent of a stress or strain tensor.
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Parameters
----------
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T_sym : numpy.ndarray of shape (...,3,3)
Symmetric tensor of which the von Mises equivalent is computed.
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s : float
Scaling factor (2/3 for strain, 3/2 for stress).
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"""
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d = _tensor.deviatoric(T_sym)
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return _np.sqrt(s*_np.sum(d**2.0,axis=(-1,-2)))