Subsections

• Automatic Step Definition
• Manual Step Definition

Step Definition

It is possible to either control the generation of ABAQUS '*STEP' cards directly from within FEMGEN or to use the interface defaults. Where simple structural or heat transfer analyses are most commonly performed it is likely that the interface defaults are the most convenient. For more complex analyses direct control over the step cards may be required.

Automatic Step Definition

The interface checks for element types (such as gap or interface elements) which are likely to imply nonlinearity. It then generates '*STEP' cards as follows:

For linear analyses the interface produces the following cards for all steps:

*STEP, PERTURBATION

except for analyses, such as heat transfer, where the option 'PERTURBATION' is inappropriate; the following card is then produced:

*STEP

For nonlinear analyses the interface produces the following card for all steps:

*STEP, INC=100, NLGEOM

except in heat transfer analyses where the option 'NLGEOM' is omitted.

The above cards are suitable for ABAQUS 5.2 and later versions but note that the actual ABAQUS cards produced will depend upon the setting of the resource *.abaqus.version (see section 1.4).

Manual Step Definition

Direct step control is achieved via FEMGEN load type 'STEP-DEF'. This load type does not appear in the menus but may be defined in the same way as other loads. The user should supply a 'STEP-DEF' load type for each FEMGEN loadcase/ABAQUS step. It is used to control both the step type and certain general characteristics of the step.

Example FEMGEN Command for first loadcase/step:

PROPERTY LOAD STEP-DEF [name] lcase_no ALL arg1 arg2 arg3 arg4 arg5 arg6

Table 6.1 below shows the meanings of the command arguments.

Note that the specific ABAQUS cards produced will depend upon the setting of the resource *.abaqus.version (see section 1.4). Arguments 5 and 6 are only needed for ABAQUS 4.9 to specify nonlinear convergence tolerances. ABAQUS 5.2 and later versions calculate these tolerances internally.

Argument Value Meaning

1 0 retain loads from previous steps (OP=MOD)

1 remove loads from previous steps (OP=NEW)

2 0 This step is linear (PERTURBATION)

1 This step is nonlinear (NLGEOM)

2 Neither PERTURBATION or NLGEOM is specified

3 0 EXTRAPOLATION is LINEAR (default)

1 EXTRAPOLATION is set to NO

2 EXTRAPOLATION is set to PARABOLIC

4 0 The following procedure is steady state

1 The following procedure is transient

5 'real1' First Convergence Tolerance (e.g.PTOL)

6 'real2' Second Convergence Tolerance (e.g.MTOL)