FEA Procedure - mesh, properties

Creating the model.

The model is drawn in 1D, 2D or 3D space in the appropriate units (M, mm, in, etc..). The model may be created in the pre-processor, or it can be imported from another CAD package via a neutral file format (IGES, STEP, ACIS, Parasolid, DXF, etc.) Defining the element type, this may be 1D, 2D or 3D, and specific to the analysis type being carried out.

Applying a Mesh.

Mesh generation is the process of dividing the analysis continuum into a number of discrete parts or finite elements. The finer the mesh, the better the result, but the longer the analysis time. Therefore, a compromise between accuracy & solution speed is usually made. The mesh may be created manually, such as the one on the right, or generated automatically like the one below. In the manually created mesh, you will notice that the elements are smaller at the joint. This is known as mesh refinement, and it enables the stresses to be captured at the geometric discontinuity (the junction).

Manual meshing is a long & tedious process, but with useful tools emerging in pre-processors, the task is becoming easier. Automatic mesh generators are very useful & popular. The mesh is created automatically by a mesh engine, the only requirement is to define the mesh density along the model's edges. Automatic meshing has limitations as regards mesh quality & solution accuracy. Automatic brick element (hex) meshers are limited in function, but are steadily improving. Any mesh is usually applied to the model by simply selecting the mesh command on the preprocessor list of the gui.

Assigning Properties.

Material properties (Young’s modulus, Poisson's ratio, the density, & if applicable, coefficients of expansion, friction, thermal conductivity, damping effect, specific heat etc.) will have to be defined. Most material properties vary with temperature and it is important to understand how your material behaves under different operating conditions. The effects of material properties on FEA models are discussed further in our Finite Element Course. In addition element properties may need to be set. If 2D elements are being used, the thickness property is required. 1D beam elements require area, Ixx, Iyy, Ixy, J, & a direction cosine property which defines the direction of the beam axis in 3D space. Shell elements, which are 2½D in nature (2D elements in 3D space), require orientation & neutral surface offset parameters to be defined.

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