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*DIRECT CYCLIC
Obtain the stabilized cyclic response of a structure directly.

This option is used to provide a direct cyclic procedure for nonlinear, non-isothermal quasi-static analysis in Abaqus/Standard. It can also be used to predict progressive damage and failure for ductile bulk materials and/or to predict delamination/debonding growth at the interfaces in laminated composites in a low-cycle fatigue analysis.

Products: Abaqus/Standard  Abaqus/CAE  

Type: History data

Level: Step

Abaqus/CAE: Step module

References:

Optional parameters:

CETOL

Set this parameter equal to the maximum difference in the creep strain increment calculated from the creep strain rates based on conditions at the beginning and on conditions at the end of the increment, thus controlling the time integration accuracy of the creep integration.

This parameter can be used in conjunction with the *TIME POINTS option. In this case Abaqus/Standard will ensure the response will also be evaluated at each time point specified on the *TIME POINTS option.

If both this parameter and the DELTMX parameter are omitted, fixed time stepping will be used, with a constant time increment equal to the initial time increment or by following precisely the time points specified on the *TIME POINTS option.

CONTINUE

Set CONTINUE=YES to specify that the current *DIRECT CYCLIC step is a continuation of the previous direct cyclic step. The displacement solution in the Fourier series obtained in the previous *DIRECT CYCLIC step is then used as the starting values for the current step.

Set CONTINUE=NO (default) to reset all the displacement Fourier coefficients to zero, thus allowing application of cyclic loading conditions that are very different from those in the previous direct cyclic step.

DELTMX

Set this parameter equal to the maximum temperature change to be allowed in an increment during a direct cyclic analysis. Abaqus/Standard will restrict the time increment to ensure that this value will not be exceeded at any node during any increment of the step.

This parameter can be used in conjunction with the *TIME POINTS option. In this case Abaqus/Standard will ensure the response will also be evaluated at each time point specified on the *TIME POINTS option.

If both this parameter and the CETOL parameter are omitted, fixed time stepping will be used, with a constant time increment equal to the initial time increment or by following precisely the time points specified on the *TIME POINTS option.

FATIGUE

Include this parameter to perform a low-cycle fatigue analysis using a direct cyclic approach in conjunction with the damage extrapolation technique. Multiple cycles can be included in a single direct cyclic analysis. The analysis models progressive damage and failure on constitutive points in the bulk materials based on a continuum damage approach. It can also be used to model delamination/debonding growth at the interfaces in laminated composites.

TIME POINTS

Set this parameter equal to the name of the *TIME POINTS option that defines the time points at which the response of the structure will be evaluated.

Data line to control incrementation and Fourier representation in a direct cyclic analysis without the FATIGUE parameter: 

First (and only) line:

  1. Initial time increment. If this entry is omitted, a default value of 0.1 times the single loading cycle period is assumed. If automatic incrementation is used, this should be a reasonable suggestion for the initial increment size and will be adjusted as necessary. If direct incrementation is used, this entry will be used as the constant time incrementation or will be ignored if the *TIME POINTS option is specified.

  2. Time of a single loading cycle.

  3. Minimum time increment allowed. This entry is used only if the CETOL or DELTMX parameter is specified. If this entry is omitted, a default value of the smaller of the suggested initial time increment or 10–5 times the single loading cycle period is assumed.

  4. Maximum time increment allowed. This entry is used only if the CETOL or DELTMX parameter is specified. If this entry is omitted, the upper limit is equal to 0.1 times the single loading cycle period.

  5. Initial number of terms in the Fourier series. The value must be greater than 0 and less than 500. It cannot be greater than half of the time of a single loading cycle divided by the initial time increment. If the *TIME POINTS option is used, the number of terms in the Fourier series must be less than half of the number of time points specified. Abaqus/Standard will automatically adjust the number of Fourier terms used in the analysis if such a condition is not satisfied. The default is 11.

  6. Maximum number of terms in the Fourier series. It must be greater than 0 and less than 500. The default is 25.

  7. Increment in number of terms in the Fourier series. The default is 5.

  8. Maximum number of iterations allowed in a step. The default is 200.

Data lines for a low-cycle fatigue analysis using the direct cyclic approach: 

First line:

  1. Initial time increment. If this entry is omitted, a default value of 0.1 times the single loading cycle period is assumed. If automatic incrementation is used, this should be a reasonable suggestion for the initial increment size and will be adjusted as necessary. If direct incrementation is used, this entry will be used as the constant time incrementation or will be ignored if the *TIME POINTS option is specified.

  2. Time of a single loading cycle.

  3. Minimum time increment allowed. This entry is used only if the CETOL or DELTMX parameter is specified. If this entry is omitted, a default value of the smaller of the suggested initial time increment or 10–5 times the single loading cycle period is assumed.

  4. Maximum time increment allowed. This entry is used only if the CETOL or DELTMX parameter is specified. If this entry is omitted, the upper limit is equal to 0.1 times the single loading cycle period.

  5. Initial number of terms in the Fourier series. The value must be greater than 0 and less than 500. It cannot be greater than half of the time of a single loading cycle divided by the initial time increment. If the *TIME POINTS option is used, the number of terms in the Fourier series must be less than half of the number of time points specified. Abaqus/Standard will automatically adjust the number of Fourier terms used in the analysis if such a condition is not satisfied. The default is 11.

  6. Maximum number of terms in the Fourier series. It must be greater than 0 and less than 500. The default is 25.

  7. Increment in number of terms in the Fourier series. The default is 5.

  8. Maximum number of iterations allowed in a step. The default is 200.

Second line:

  1. Minimum increment in number of cycles over which the damage is extrapolated forward. It must be greater than 0, and the default is 100. This value is most relevant for progressive damage and failure in bulk materials.

  2. Maximum increment in number of cycles over which the damage is extrapolated forward. It must be greater than 0, and the default is 1000. This value is most relevant for progressive damage and failure in bulk materials.

  3. Total number of cycles allowed in a step. If this entry is zero or not specified, the default value is equal to one plus half of the maximum increment in number of cycles over which the damage is extrapolated.

  4. Damage extrapolation tolerance. The maximum extrapolated damage increment will be limited by this value. The default is 1.0.

  5. Tolerance for the least number of cycles to fracture an element. The default is 0.