**process initiation

Description

This post processor is used to estimate the time to crack initiation. For a cycle the initiation damage is calculated by the following expression:

(151)\[I_a=\frac{1}{c}\int_{cycle} \left<\frac{<SII-Sla(1-Dox)}{(1-Dox)-S_{max}^{eq}}\right>^b dN\]

with

(152)\[Sla = Sla0 (1-h\overline{{\bf Trace}(S)})\]

and \(Dox=\sqrt{N/Nox}\) if we’re taking into account the effect of oxidation, \(Dox=0\) otherwise.

A single output map is generated for the total history of loading. The number of cycles to initiation \(N_a\) which corresponds to the moment where the damage attains a value of 1. The variable name generated is Na in the problem.utp file. The number of oxidation cycles ahead of the start of initiation (stress lower than the fatigue limit) is also saved with the name Na-ox.

Syntax

**process initiation \(~\,\) *var name [ *type scalar | tensor ] [ *normalized_coeff] [ *oxidation [section1] ] [ *range section2 ]

name is the variable name. It is systematically normalized by the coefficient sigma_u given in the material file.

The option *oxidation is optional. If it is present, it can be followed by the number of section containing the user input for oxidation. Otherwise the oxidation will be initialized with its default values.

For multi-dimensional loading the amplitude calculation will be made using a range type post-computation. In order to be able to input options to the range processor, the user can give a section number for that user input after the *range keyword.

The coefficients Sla0 and h are given normed or not. If they are normalized (the option *normalized_coeff was given), the expected names in the material file will be N_Sla0 N_h. The other coefficients which must be input are b and c.

Example

% a complete example
**process initiation
  *var sig
  *oxidation
  *norm
  *normalized_coeff

%with the following syntax in the material file :
**process initiation
  sigma_u  130.
  N_h      5.2
  N_Sla0   0.023
  b  2.
  c  3500.