# pymatgen.analysis.elasticity.stress module¶

This module provides the Stress class used to create, manipulate, and calculate relevant properties of the stress tensor.

class Stress(stress_matrix)[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

property dev_principal_invariants[source]

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

property deviator_stress[source]

returns the deviatoric component of the stress

property mean_stress[source]

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

symbol = 's'[source]
property von_mises[source]

returns the von mises stress