**process charkaluk#

Description#

This post-processor is an energetic damage criterion based on the inelastic energy dissipated per cycle [U10]. The dissipated energy is defined as

\[\Delta W = \int \ten{\sigma} : d\ten{\varepsilon}^{\mathrm{inel}},\]

optionally normalized by a reference stress \(\sigma_u\). The fatigue life (or damage indicator) is then given by

\[N_f = \frac{1}{K \, (\Delta W)^A},\]

where \(K\) and \(A\) are material parameters identified from experimental data.

Syntax#

**process charkaluk \(~\,\) *stress stress \(~\,\) *strain strain [ *precision prec ] [ *infinity_is infty ] [ *no_sqrt2 ]

*stress stress

the name of the stress tensor.

*strain strain

the name of the inelastic strain tensor.

 *precision prec

precision for Runge-Kutta integration (required when parameters are not constant).

*infinity_is infty

max value of number cycles to failure (default: 1e15).

*no_sqrt2

a flag to not multiply strain shear components by \(\sqrt2\) (default false).

Output:

  • Nr: damage, or the inverse of number of cycles to failure.

  • DWp: the inelastic dissipated energy density per cycle.

Example#

***local_post_processing
 **file integ
 **elset ALL_ELEMENT
 **material_file charkaluk.mat
 **process charkaluk
  *stress sig
  *strain epi

The coefficients \(A\) and \(K\) should be given in a material file as

% charkaluk.mat
***post_processing_data
 **process charkaluk
   A  -1.572
   K  0.593
   sigma_u temperature
   515.  20.
   515.  300.
   250.  500.
   110.  700.
   110.  800.
   72.   950.
***return