# pymatgen.analysis.elasticity.stress module¶

class Stress[source]

This class extends SquareTensor as a representation of the stress

Create a Stress object. Note that the constructor uses __new__ rather than __init__ according to the standard method of subclassing numpy ndarrays.

Parameters: stress_matrix (3x3 array-like) – the 3x3 array-like representing the stress
dev_principal_invariants

returns the principal invariants of the deviatoric stress tensor, which is calculated by finding the coefficients of the characteristic polynomial of the stress tensor minus the identity times the mean stress

deviator_stress

returns the deviatoric component of the stress

mean_stress

returns the mean stress

piola_kirchoff_1(def_grad)[source]

calculates the first Piola-Kirchoff stress

Parameters: def_grad (3x3 array-like) – deformation gradient tensor
piola_kirchoff_2(def_grad)[source]

calculates the second Piola-Kirchoff stress

Parameters: def_grad (3x3 array-like) – rate of deformation tensor
von_mises

returns the von mises stress