**process oxidation

Description

This post-processor can be used to quantify the effects of oxidation which contributes to the mechanisms of damage.

We calculate, for a cycle, the oxidation damage \(I_{ox}\) with the following expression:

\[I_{ox}=\int_{cycle} {\left ( \frac{K0}{e0} exp\left(\frac{-Q}{{RT}}\right) \left [ 1 + \left < \frac{S-S_{lox}}{B} \right >\right ]^m \right ) ^2}dN\]

with

\[S = (1-\alpha-\beta){\bf Mises}(\ten \sigma)+\alpha{\bf Eig1}(\ten \sigma) +\beta{\bf Trace}(\ten \sigma)\]

and

\[Slox = Slox0 (1-h{\bf Trace}(\ten \sigma)) + {\bf Trace}(\ten \sigma)\]

The output is generated as a single map for the whole loading history. The cycle number is \(N_{ox}\), defined as the inverse of oxidation damage per cycle and denoted Nox in the output.

Syntax

**process oxidation \(~\,\) *var name [*type scalar | tensor ] [*delay ] [*norm [*normalized_coeff ]] [*isotherm ]

name is the variable name to treat. If the option *norm is specified the subject variable will be normed by the coefficient sigma_u furnished in the material file.

With the option *delay the lag stress \(S'\) will be used. The lag stress is computed from

\[dS'=\frac{S-S'}{\tau}\]

The coefficients B, Slox0, and h are to be given in the material file regardless of the use of normalization. If they are normalized (option *normalized_coeff) the expected names in the material file will be N_B, N_Slox0 and N_h.

With the option *isotherm the temperature is read in the material file using a “coefficient” temperature. Otherwise the temperature must be included in the output files (use the **save_parameter output option in the FEA calculation.

alpha and beta are optional coefficients, having a zero value by default. The other coefficients which must be input are m, K0, e0 and Q. The additional coefficient tau must be supplied if the *delay option was input.

Example

% a simple example
**process oxidation
  *var sig
  *norm

% The following syntax must be used in the material file :
**process oxidation
  sigma_u 850.
  B       46.5
  m       2.5
  Slox0   0.12
  h       3.5
  e0      50.e-06
  K0      1.42
  Q       214.