With the variety of technologies available in many elements, choosing the best settings to solve your problem efficiently can be challenging. Particularly in the newer structural and solid elements for stress analysis, an element might offer two to four technologies.
The program can offer suggestions (or reset the technology settings) to help you achieve the best solution via ETCONTROL. The command helps you to select the appropriate element technologies by considering the stress state, the options set on the element type, and the associated constitutive models of the element type. ETCONTROL supports all applicable current-technology elements.
The materials associated with each element type are detected at the solution stage and are classified as:
Elastoplastic materials, including:
Linear elastic materials with Poisson's ratio <= 0.49
Linear elastic materials with Poisson's ratio > 0.49
Anisotropic materials (not including orthotropic materials defined via MP)
Elastoplastic materials (other nonlinear materials except hyperelastic materials)
Hyperelastic materials, including:
Nearly incompressible hyperelastic materials
Fully incompressible hyperelastic materials
In practical application, one element type could be associated with more than one constitutive model, for example, linear elastic and elastoplastic materials. For this case, the suggestions/resettings are based on elastoplastic materials, which need more complicated element technology. The list of constitutive models above is organized in order of complexity, with the bottom ones more difficult to solve numerically. When an element type is associated with multiple constitutive models, the more complex one is used in the automatic selection of the element technology.
When using ETCONTROL, the suggestions given or settings changed are described in the tables below.
Table 5.4: Recommendation Criteria for Element Technology (Linear Material)
| Linear Materials Only | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Element | Stress State / Option | Poisson's ratio (ν) <= 0.49 | Poisson's ratio (ν) > 0.49 (or anisotropic materials) | ||||||
| SHELL181 | Default | KEYOPT(3) = 2 for higher accuracy of membrane stress, otherwise, KEYOPT(3) = 0; KEYOPT(8) = 2 for all cases | |||||||
| Membrane-only option (KEYOPT(1) = 1) | KEYOPT(3) = 2 for higher accuracy of stress, otherwise, KEYOPT(3) = 0; KEYOPT(8) = 0 for all cases | ||||||||
| SOLID272 | KEYOPT(6) = 0 | KEYOPT(6) = 1 | |||||||
| SOLID273 | No change. (Default element settings are best.) | ||||||||
| SOLID285 | No change. (Default element settings are best.) | ||||||||
| PLANE182 | Plane stress | KEYOPT(1) = 2 | |||||||
| Not plane stress | KEYOPT(1) = 3 [a] | KEYOPT(1) = 2 | |||||||
| PLANE183 | Plane stress | No change. (Default element settings are best.) | |||||||
| Not plane stress | No change. (Default element settings are best.) | ||||||||
| SOLID185 | KEYOPT(2) = 3 [a] | KEYOPT(2) = 2 | |||||||
| SOLID186 | KEYOPT(2) = 0[b] | ||||||||
| SOLID187 | No change. (Default element settings are best.) | ||||||||
| SOLID285 | KEYOPT(1) = 0 | ||||||||
| BEAM188 | KEYOPT(3) = 2, KEYOPT(1) = 1 [c] | ||||||||
| BEAM189 | KEYOPT(1) = 1 [c] | ||||||||
| SHELL208 | KEYOPT(8) = 2 | ||||||||
| SHELL209 | KEYOPT(8) = 2 | ||||||||
| SHELL281 | No change. (Default element settings are best.) | ||||||||
| PIPE288 |
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| PIPE289 |
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[a] If the material is orthotropic, set the KEYOPT to 2 (so that the program considers the material to be anisotropic).
[b] Full integration (KEYOPT(2)=1) will be suggested or used with SOLID186 when coupled field elements PLANE222, PLANE223, SOLID225, SOLID226, and SOLID227 are present in the same model.
[c] Only when the element section is not circular; otherwise, KEYOPT(1) = 0.
[d] Only when the element cross section is composite; otherwise, KEYOPT(15) = 0.
Table 5.5: Recommendation Criteria for Element Technology (Nonlinear Materials)
| Nonlinear Materials | ||||||
|---|---|---|---|---|---|---|
| Element | Stress State / Option | Elastoplastic materials (may also have hyperelastic materials) | Hyperelastic materials only | |||
| SHELL181 | Default | KEYOPT(3) = 2 for higher accuracy of membrane stress, otherwise, KEYOPT(3) = 0; KEYOPT(8) = 2 for all cases | KEYOPT(3) = 0, KEYOPT(8) = 0 | |||
| Membrane-only option (KEYOPT(1) = 1) | KEYOPT(3) = 2 for higher accuracy of stress, otherwise, KEYOPT(3) = 0; KEYOPT(8) = 0 for all cases | KEYOPT(3) = 0, KEYOPT(8) = 0 | ||||
| PLANE182 | Plane stress | KEYOPT(1) = 2 | KEYOPT(1) = 0 | |||
| Not plane stress | KEYOPT(1) = 2 [a] | KEYOPT(1) = 0 [a] | ||||
| PLANE183 | Plane stress | No change. (Default element settings are best.) | ||||
| Not plane stress | no change (default element settings are best) [a] | |||||
| SOLID185 | KEYOPT(2) = 2 [a] | KEYOPT(2) = 0 [a] | ||||
| SOLID186 | KEYOPT(2) = 0 [a] | |||||
| SOLID187 | No change. (Default element settings are best.) [a] | |||||
| SOLID272 | KEYOPT(6) = 1 | |||||
| SOLID273 | No change. (Default element settings are best.) [a] | |||||
| SOLID285 | KEYOPT(1) = 0 | |||||
| BEAM188 | KEYOPT(3) = 2, KEYOPT(1) = 1 [b] | |||||
| BEAM189 | KEYOPT(1) = 1 [b] | |||||
| SHELL208 | KEYOPT(8) = 2 | KEYOPT(8) = 0 | ||||
| SHELL209 | KEYOPT(8) = 2 | KEYOPT(8) = 0 | ||||
| SHELL281 | No change. (Default element settings are best.) | |||||
| PIPE288 |
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| PIPE289 |
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[a] If even one of your hyperelastic materials is fully incompressible, then KEYOPT(6) = 1 is required. Therefore, Ansys, Inc. recommends using a different element type for such materials to avoid using the more costly mixed u-P formulation where it is not needed.
[b] Only when the element section is not circular, otherwise KEYOPT(1) = 0.
[c] Only when the element cross section is composite; otherwise, KEYOPT(15) = 0
For the solid elements listed above, ETCONTROL provides suggestions or resets the KEYOPTs for the element technology settings (such as KEYOPT(1) for PLANE182, KEYOPT(2) for SOLID185 and SOLID186). The mixed u-P formulation KEYOPT(6) (for PLANE182, PLANE183, SOLID185, SOLID186, SOLID187, SOLID272, SOLID273) or KEYOPT(1) (for SOLID285) is reset when necessary (that is, when fully incompressible hyperelastic materials are associated with non-plane stress states).
For BEAM188 and BEAM189, KEYOPT(1) is always suggested for non-circular cross section beams and should be reset when ETCONTROL,SET,.. is issued. However, the KEYOPT setting changes the number of degrees of freedom at each node, so it must be set before you issue D, DK, DA, or similar commands. Because the ETCONTROL reset occurs at the beginning of solution, a message appears indicating stating that you should change KEYOPT(1) to 1, but the change does not occur automatically.
For SHELL181, the setting for KEYOPT(3) depends on whether the element type is associated with any non-hyperelastic materials. If it is, the program cannot reset it automatically, but it displays a message with the recommended setting (even if you issued ETCONTROL,SET). Reset manually if the defined criteria matches your problem.
For the coupled-field elements PLANE222, PLANE223, SOLID225, SOLID226, and SOLID227, see the individual element descriptions for information about ETCONTROL suggestions/resettings.
If an element type is defined but not associated with any material, no suggestions or resets are done for that element type. The stress states and options are mentioned only when they affect the suggestions or settings. The suggestions are available in output.
All nonlinear stress/strain data should be input as true-stress/true-(logarithmic-) strain. Accordingly, all output data is also indicated as true-stress/true-strain. For small strains, the true-stress/true-strain data and engineering-stress/engineering-strain data are essentially identical.