SOLID285 Element Description

SOLID285 element is a lower-order 3-D, 4-node mixed u-P element. The element has a linear displacement and hydrostatic pressure behavior. The element is suitable for modeling irregular meshes (such as those generated by various CAD/CAM systems) and general materials (including incompressible materials).

The element is defined by four nodes having four degrees of freedom at each node: three translations in the nodal x, y, and z directions, and one hydrostatic pressure (HDSP) for all materials except nearly incompressible hyperelastic materials. For nearly incompressible materials, instead of hydrostatic pressure, the volume change rate is used at each node together with the three translation degrees of freedom. In a nonlinear analysis, you can control the tolerance of HDSP separately via the CNVTOL command.

The element has plasticity, hyperelasticity, creep, stress stiffening, large deflection, and large strain capabilities. It is capable of simulating deformations of nearly incompressible elastoplastic materials, nearly incompressible hyperelastic materials, and fully incompressible hyperelastic materials.

For more details about this element, see SOLID285.

Figure 285.1:  SOLID285 Geometry

SOLID285 Input Data

The geometry, node locations, and the coordinate system for this element are shown in Figure 285.1: SOLID285 Geometry.

In addition to the nodes, the element input data includes the orthotropic or anisotropic material properties. Orthotropic and anisotropic material directions correspond to the element coordinate directions. The element coordinate system orientation is as described in the Material Reference.

Element loads are described in Nodal Loading. Pressure loads may be input as surface loads on the element faces as shown by the circled numbers on Figure 285.1: SOLID285 Geometry. Positive pressures act into the element. Temperatures may be input as element body loads at the nodes. The node I temperature T(I) defaults to TUNIF. If all other temperatures are unspecified, they default to T(I). For any other input temperature pattern, unspecified temperatures default to TUNIF.

As described in Coordinate Systems, you can use ESYS to orient the material properties and strain/stress output. Use RSYS to choose output that follows the material coordinate system or the global coordinate system.

KEYOPT(16) = 1 activates steady state analysis (defined via the SSTATE command). For more information, see Steady State Rolling in the Mechanical APDL Theory Reference.

You can apply an initial stress state to this element via the INISTATE command. For more information, see Initial State in the Mechanical APDL Advanced Analysis Guide.

The effects of pressure load stiffness are automatically included for this element. If an unsymmetric matrix is needed for pressure load stiffness effects, use NROPT,UNSYM.

The next table summarizes the element input. Element Input gives a general description of element input.

Solid 285 Element Technology

This element has only a mixed u-P formulation with pressure stabilization. For more information, see Element Technologies.

SOLID285 Output Data

The solution output associated with the element is in two forms:

Several items are illustrated in Figure 285.2: SOLID285 Stress Output. The element stress directions are parallel to the element coordinate system. A general description of solution output is given in The Item and Sequence Number Table. See the Basic Analysis Guide for ways to view results.

Figure 285.2:  SOLID285 Stress Output

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.

In either the O or R columns, “Y” indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.

Table 285.2: SOLID285 Item and Sequence Numbers lists output available through ETABLE using the Sequence Number method. See The General Postprocessor (POST1) and The Item and Sequence Number Table in this document for more information. The following notation is used in Table 285.2: SOLID285 Item and Sequence Numbers:

SOLID285 Assumptions and Restrictions

SOLID285 Product Restrictions

When used in the product(s) listed below, the stated product-specific restrictions apply to this element in addition to the general assumptions and restrictions given in the previous section.

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