5.8. Automatic Selection of Element Technologies and Formulations

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 the ETCONTROL command. 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:

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 DefaultKEYOPT(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) = 0KEYOPT(6) = 1
SOLID273  No change. (Default element settings are best.)
SOLID285  No change. (Default element settings are best.)
PLANE182 Plane stressKEYOPT(1) = 2
Not plane stressKEYOPT(1) = 3 [1]KEYOPT(1) = 2
PLANE183 Plane stressNo change. (Default element settings are best.)
Not plane stressNo change. (Default element settings are best.)
SOLID185  KEYOPT(2) = 3 [1]KEYOPT(2) = 2
SOLID186  KEYOPT(2) = 0
SOLID187  No change. (Default element settings are best.)
BEAM188  KEYOPT(3) = 2, KEYOPT(1) = 1 [2]
BEAM189  KEYOPT(1) = 1 [2]
SHELL208  KEYOPT(8) = 2
SHELL209  KEYOPT(8) = 2
SHELL281  No change. (Default element settings are best.)
PIPE288  
KEYOPT(3) = 2
KEYOPT(4) = 2
KEYOPT(15) = 1 [3]
KEYOPT(3) = 2
KEYOPT(4) = 1
KEYOPT(15) = 1 [3]
PIPE289  
KEYOPT(4) = 2
KEYOPT(15) = 1 [3]
KEYOPT(4) = 1
KEYOPT(15) = 1 [3]


  1. If the material is orthotropic, set the KEYOPT to 2 (so that the program considers the material to be anisotropic).

  2. Only when the element section is not circular; otherwise, KEYOPT(1) = 0.

  3. 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 DefaultKEYOPT(3) = 2 for higher accuracy of membrane stress, otherwise, KEYOPT(3) = 0;  KEYOPT(8) = 2 for all casesKEYOPT(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 casesKEYOPT(3) = 0, KEYOPT(8) = 0
PLANE182 Plane stressKEYOPT(1) = 2KEYOPT(1) = 0
Not plane stressKEYOPT(1) = 2 [1]KEYOPT(1) = 0 [1]
PLANE183 Plane stressNo change. (Default element settings are best.)
Not plane stressno change (default element settings are best) [1]
SOLID185  KEYOPT(2) = 2 [1]KEYOPT(2) = 0 [1]
SOLID186  KEYOPT(2) = 0 [1]
SOLID187  No change. (Default element settings are best.) [1]
SOLID272  KEYOPT(6) = 1
SOLID273  No change. (Default element settings are best.) [1]
SOLID285  No change. (Default element settings are best.)
BEAM188  KEYOPT(3) = 2, KEYOPT(1) = 1 [2]
BEAM189  KEYOPT(1) = 1 [2]
SHELL208  KEYOPT(8) = 2KEYOPT(8) = 0
SHELL209  KEYOPT(8) = 2KEYOPT(8) = 0
SHELL281  No change. (Default element settings are best.)
PIPE288  
KEYOPT(3) = 2
KEYOPT(4) = 2
KEYOPT(15) = 1 [3]
PIPE289  
KEYOPT(4) = 2
KEYOPT(15) = 1 [3]


  1. 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.

  2. Only when the element section is not circular, otherwise KEYOPT(1) = 0.

  3. 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 (i.e., KEYOPT(1) for PLANE182, KEYOPT(2) for SOLID185 and SOLID186). The Mixed u-P formulation KEYOPT(6) 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 any D, DK, DA, and similar commands. Because the ETCONTROL reset is done at the beginning of the solution stage, 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 your problem and your purpose if the element type is associated with any non-hyperelastic materials. In this case, the program cannot reset it automatically, but it displays a message with the recommended setting (even if you used ETCONTROL,SET,..). You should reset this manually if the defined criteria matches your problem.

For the coupled-field elements PLANE223, SOLID226, and SOLID227, see the individual element descriptions in the Element Reference for information on 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.


Release 18.2 - © ANSYS, Inc. All rights reserved.