Finite Element Analysis is only as reliable as the assumptions you put into it. You can have a perfectly meshed model and a powerful solver, but if your boundary conditions are wrong, your results are meaningless. After years of running simulations and reviewing other engineers’ models, I’ve seen the same mistakes come up again and again.
1. Over-Constraining the Model (Fixed Support Everywhere)
The most common mistake beginners make is applying a Fixed Geometry constraint to an entire face when only specific degrees of freedom should be restrained.
What goes wrong: A fixed support locks all six degrees of freedom — three translational, three rotational. Applied to the wrong face, it artificially stiffens the model and produces stress concentrations that don’t exist in reality.
The fix: Think physically. Ask yourself: what is actually stopping this part from moving in the real world? Use roller/slider constraints for surfaces that can slide, and pin constraints for holes that are bolted but free to rotate.
2. Applying Loads to the Wrong Geometry
Pressure loads applied to an entire face when the force only acts on a small region will spread the load incorrectly and underestimate peak stresses.
The fix: Use split lines in SOLIDWORKS to create a face that matches the actual contact area, then apply the load only to that region. This is especially critical for contact patches, weld joints, and localised thermal loads.
3. Ignoring Symmetry
Many engineers model the full geometry when a symmetry boundary condition would let them run a much finer mesh on half (or a quarter) of the model in the same compute time.
The fix: Identify planes of symmetry in both geometry and loading. Apply a Symmetry fixture to the cut face — this constrains normal displacement and the two in-plane rotations, correctly representing the cut surface behaviour.
4. Mixing Up Pressure and Force
SOLIDWORKS Simulation distinguishes between Force (total load distributed over a face) and Pressure (load per unit area). Using the wrong one gives results that are off by the area factor.
The fix: If you know the total reaction force (e.g., from a datasheet), use Force. If you know the contact pressure from a seal specification or hydraulic calculation, use Pressure. Never guess.
5. Forgetting Thermal Boundary Conditions in Coupled Analyses
In thermal-structural analyses, engineers often set mechanical constraints but forget to define thermal boundary conditions correctly — leaving surfaces adiabatic when they should be convecting to ambient air.
The fix: Define convection coefficients on all free surfaces. For natural convection on a vertical surface in still air, a value of 5–10 W/m²·K is a reasonable starting point. For forced convection, calculate from your CFD results or use correlations.
Getting boundary conditions right is not glamorous work — it’s methodical and requires a clear physical understanding of the problem. But it separates simulations that inform decisions from simulations that give false confidence.
If you’re working on a complex FEA setup and want a second opinion on your boundary conditions or mesh strategy, feel free to reach out.