Interpreting FEA Results

Bob Williams
Product Manager
ALGOR, Inc.
Pittsburgh, PA

One of the most important steps in the FEA process begins after the model has been built and analyzed. This is when an engineer can examine the results, determine what they mean and then make decisions about whether a design needs modified. Interpreting FEA results is where engineers, based on their knowledge and experience, add great value as they make sense of the numerical and graphical output and decide if a design is acceptable and ready for manufacturing.

FEA vendors like ALGOR have made building models and analyzing them increasingly easy and fast, which frees up valuable time for engineers to focus on fully understanding the results. To even further increase productivity, the FEA software should also provide powerful, flexible tools for looking at results and assessing designs quickly, thoroughly and accurately.

For example, the ALGOR FEMPRO single-user interface includes a wide range of results evaluation and presentation options, which are available for all of ALGOR's simulation capabilities. The integrated results environment enables users to easily examine analysis results as graphical displays of color-coded contours; inquire at locations of interest to obtain detailed numerical data; create result graphs using built-in, virtual instrumentation; and create and display animations and graphics to be used with other result presentation capabilities.

Tools for Result Interpretation

One important tool that aids the result interpretation process is the display of precision contours, which show a graphical representation of the stepped changes in results from one element to the next. This calculation checks the model for compliance with the assumptions of FEA theory and can be used to determine the effect of the mesh on result accuracy and as guidance for locating the areas needing localized mesh refinement.

Another useful result interpretation tool is the ability to specify allowable stress values and then display factor of safety contours to see where stresses in the model are below and above those allowables. Viewing factor of safety contours can help users properly exercise engineering judgment when balancing between material and cost reduction and ensuring a safe product.

In addition to checking result precision and the factor of safety for a design, engineers often need to know the distribution of stress through the thickness of a thin-walled part, particularly when relating 3-D solid FEA models of thin-walled pressure vessels to the relevant ASME codes. A stress linearization utility can help engineers easily evaluate their designs' compliance with industry standards such as the ASME Boiler and Pressure Vessel Code (BPVC). With this utility, a Stress Classification Line (SCL) is defined and then the software automatically calculates the linearized stress distribution and formats results for easy comparison with code requirements.

Result evaluation and interpretation capabilities such as precision contours, factor of safety contours and stress linearization help automate typical FEA or engineering processes so that engineers can focus on determining what the results say about the adequacy of a design. Supporting these tools is often a number of visualization features that make this process even easier:

• Annotations to highlight the location of minimum and maximum results make it easy and fast to locate the areas of interest. Zooming in on those areas and toggling between the result and precision contours then helps determine if the mesh is adequate in those areas or needs refined.
• A slider for controlling the display of elements based on a lower or upper result limit allows for a threshold value to be set so that only results within the specified range are displayed. This also lets engineers quickly see what areas need to be examined closer and where design changes may be needed.
• Transparent display capabilities (translucency) help engineers view and present results on complex assemblies while keeping the areas of interest in proper context.

Effect of Engineering Judgment

As mentioned earlier, an engineer must use his or her knowledge and experience to interpret FEA results and decide whether design changes need to be made. Often, this leads to an iterative process of redesigning, retesting and reevaluating, which is supported by ALGOR's InCAD technology featuring direct CAD/CAE data exchange including full associativity with each design change made in leading CAD packages.

When engineers make design changes in their CAD solid modeler, a new mesh is created and any surface-based loads or constraints, element types, material properties and analysis parameters are automatically updated with each change. Associating the FEA data directly with the CAD geometry saves engineers time by enabling them to more quickly perform the multiple iterations often needed to optimize product designs and, once again, focus their time on interpreting the FEA results.

Presenting Findings

Finally, once an engineer is satisfied with the results and design, they need to communicate their findings with others. ALGOR's report wizard automatically collects information related to an analysis and generates an organized, professional report, which is supported by a wide range of image and animation options along with report customization tools. These reports can then be instantly shared with managers, colleagues or clients by publishing them to any Internet or Intranet site. Alternatively, the generated report can be attached as an appendix within any design report.

Today's powerful, flexible result evaluation and presentation tools help engineers spend valuable time interpreting FEA results, making proper design decisions and changes and then communicating findings, which helps companies speed up time to market and make better, safer products at a lower cost.