Checklist to Ensure Validity of Your Finite Element Structural Analysis
Posted by Bhaumik Dave on February 9th, 2016
It is a common phenomenon across most of the manufacturing firms to employ simulation into multiple stages of product development to improve efficiency and achieve cost reduction. Simulation tools have stood the test of time and have supported design engineers proactively.
However, it is important that organizations use techniques like FEA and CFD with strict accountability and integrate the process of verification and validation, most commonly known as V&V into the design process.
Verification and Validation are backbone for simulation, providing assurance about the safety and reliability of the product designs determined virtually. Ignoring the V&V process will have harmful repercussions and might take the design process in the wrong direction, increasing the cost and time significantly.
Why Verification and Validation is Important?
To understand the importance of V&V, it is important to understand the FEA solvers always give approximate solutions and are not robust. There always chances of errors while modeling or defining boundary conditions which together can lead to massive errors in the final results. As an example, consider performing a structural analysis on an automobile connecting rod subjected to loads resulting from piston and crankshaft movements. You might develop a clean CAD model to perform the analysis and feed in all the boundary conditions using slightly incorrect force direction or magnitude and solve the geometry.
Looking at the stress plot generated, you then look for possible optimization opportunities and finalize the design. The error generated might not provide large variations with hand calculations, but might affect the fatigue life considerably. These types of errors are very common and sometimes these errors might be so small to even identify, but will have major impact on the performance or service life. Verification and validation is thus important to ensure that simulation help does not turn into a problem.
Checklist to Verify Structural Analysis
Here’s a checklist or a set of questionnaire to help you out in verifying your analysis:
- Has the dimensions of FEA model been verified against the actual part dimensions?
- Are the material properties correct and assigned to appropriate model regions?
- How good is the mesh quality and is it refined enough to generate accurate results?
- Have you verified the model for mesh-sensitivity?
- Are the element properties and types like beam and shell properly associated with the model regions?
- Do the selected elements pass the shape distortion test criteria?
- Are the applied loads and constraints accurate in terms of location, magnitude or direction?
- Has the free thermal expansion and rigid body motion tests been done for the model?
- Do the reaction forces balance the applied loads in each direction?
- How well the deformation and stress values agree with hand calculations?
- Is shear or volumetric locking a problem? Is your numerical integration scheme too low?
- Are stresses continuous across elements?
This isn’t a complete list but can help you pinpoint many error-generating possibilities and rectify them before finalizing the design. It is important to know that errors are inevitable in FEA; the chances of errors increases with increasing model complexity. What is important is to deploy a process that can help in identifying these errors before doing any damage, which is what the verification and validation is all about.