Import of Stereolithography Files

Many CAD or scanning software programs support the output of STL (stereolithography) files from scanned 3-D images or CAD objects. These STL files are commonly used for rapid prototyping in the medical and engineering fields to produce physical objects, e.g., the making of artificial replacement joints and prostheses in the medical field.

The STL file format describes the surface of an object as a collection of oriented triangles. It does not carry any other information about the object, particularly its topology (points, edges and faces) which is key for applying loads and boundary conditions on a finite element model.

ADINA is able to read an STL file and create a topological body from the surface mesh description it contains. Using the facet normal information of surface triangles, "ridges" on the surface mesh of the object are detected. This leads to the creation of points, body edges and faces, and finally to a topological body whose geometry is the surface mesh representation contained in the STL file.

Mesh densities can be applied to the body and its bounding entities (edges and faces) just like to a solid geometric body. The body's surface mesh representation is adapted to reflect the applied mesh densities. The body can then be meshed with three-dimensional tetrahedral elements for analysis. An example is shown below.

Figure 1  STL file of an engine block loaded into the AUI.
The different colors show the different body faces.

Figure 2  Surface mesh (discrete representation of body) after adaptation. Uniform subdivision for the body and finer subdivisions for the cylindrical holes.

This ADINA option to import STL files is an important feature, in addition to existing interfaces available, for the analysis of objects created in CAD or other systems.

Keywords:
Stereolithography, STL file translator, CAD import, rapid prototyping.