Product Development Simulation Results—More than Colorful Images

When analyzing simulation results, it is crucial to ask the right questions. This guide aims to help designers and developers examine key aspects to draw well-informed conclusions.

FEM simulations are now an indispensable tool in product development. However, the colorful result images are only as reliable as the models on which they are based. Designers don't need to simulate themselves—but they should know which questions to ask to assess the significance of the results.

Result Representation: When Images Deceive

Correctly interpret deformations

The visual representation of deformations is often greatly exaggerated to make effects visible. Figure 1 shows two representations of the same calculation—but which one is “correct”?

The key factor is not the visual differences, but the actual values:

• How much is the deformation scaled?
• Where is the zero point (clamping)?
• Do the absolute values meet the physical expectations?

Color scales: Red is not always "bad"

A particularly common pitfall is the choice of the color scale when red is intuitively considered critical, as shown in Figure 2. The reason for this is often the automatic scaling, which is based on the minimum and maximum—even if this maximum lies outside the displayed range.

• Was the color scale manually adjusted? If so, why?
• Are contour bands missing that make the transition between different stress regions visible?

Tip: For variation calculations, the same color scale should always be used to make changes directly comparable.

Types of stress: Which is relevant for your component?

Figure 3 shows three different stress distributions of the same calculation: the von Mises equivalent stress, the maximum principal normal stress, and the minimum principal normal stress.

Which one is relevant may depend on the material and the type of load:

• For ductile materials, the von Mises stress is often the first choice.
• Principal normal stresses are crucial for brittle materials or to distinguish between tensile and compressive areas.

Therefore, ask:

• Which type of stress is being displayed—and why?
• Is this stress actually meaningful for evaluating my component?

Meshing: The Invisible Framework of the Simulation

Meshing is often just a "black box." Yet, it plays a crucial role in determining the quality of the results.

Element types: Hexahedron vs. Tetrahedron

Figure 4 illustrates how different element types (hexahedron vs. tetrahedron) can lead to varying stress distributions. Both element types have their advantages and disadvantages:

• Hexahedrons often provide more accurate results for regular geometries with faster computation times.
• Tetrahedrons are more flexible for complex shapes but can produce local stress peaks with coarse meshing.

Questions for the simulation engineer:

• Which elements were used—and why?
• Are stress peaks caused by the element quality?
• How was mesh refinement ensured in critical areas?

Mesh density: When is the mesh fine enough?

The maximum stress increases in Figure 5 with increasing mesh refinement (from 183 MPa to 196 MPa). This highlights the consideration of stress convergence. However, not every analysis relies on complete convergence. For structural stress concepts for weld seams or investigations of deformations, coarser meshes are often sufficient. The key is that the mesh refinement matches the specific question at hand.

In general, mesh quality plays a significant role in nonlinear simulations, such as contacts.

Verify Modeling

As a customer, it is important to understand the basics of modeling.

Boundary conditions: Realistic or deliberately conservative?

The choice of boundary conditions is one of the most common sources of error in simulations. Figure 6 shows how different constraints lead to completely different stress distributions.

Since the differences are not always so obvious, you should ask the following questions:

• How realistic are the chosen boundary conditions? Do they correspond to the actual installation situation?
• Do overly rigid constraints lead to excessive or insufficient stresses?
• Would a more flexible support—for example, by including adjacent components—be more realistic?

Contacts: When components meet

Contacts can be modeled differently, as shown in Figure 7: On the left, a gap opens between the components, while on the right, the contact remains closed. Which variant is realistic?

• How were the contacts modeled (bonded, frictional, with clearance)?
• Was friction considered—and if so, with which coefficient of friction?
• What influence do the contact definitions have on the overall result?

When we look at the deformation pattern of the fixed-free bearing, the deformation appears similar to that of the open contact. Is a contact even necessary here?

Geometry: Why details matter

Figure 8 shows a classic singularity: a sharp edge leading to non-convergent stresses. If a radius is modeled instead—as usually present in reality—the stress converges with increasing mesh density.

• How detailed was the geometry modeled?
• Were geometric simplifications made? If so, what are their effects?
• How do details like holes or radii affect the result?

Evaluate Results Holistically

Plausibility: Does the result match the expectation?

A first step in evaluating simulation results is to compare them with physical intuition. Figure 9 shows the comparison of an FEM calculation with an analytical hand calculation for a simple beam. If the results agree, this is a good sign. If there are discrepancies, either the model or one's own understanding must be questioned.

• What physical principles underlie the results?
• Do the results align with your intuition and experience?
• For which conditions is the FEM model valid? Where are its limitations? What was not captured?
• Are the limitations of the simulation clear to all involved?

Result evaluation: The art of simulation

The critical evaluation of simulation results is crucial for the reliability and significance of the FEM analysis. Result evaluation means determining whether safety margins or specified limits are met, or whether optimizations are necessary.

• According to which methods, guidelines, or experiences do you want or need to evaluate?
• Critically question occurring stress peaks and singularities.
• Which evaluation criteria are being applied?

Validation: The reality check

The gold standard of simulation is the comparison with experimental data.

• Are there measurement data or tests? Is it necessary and possible to conduct experiments to verify the results?
• How well do simulation and reality align?
• How are deviations explained?

Conclusion: With Critical Questions to Well-Informed Decisions

FEM simulations are a powerful tool—but their significance depends on the quality of modeling, meshing, result representation, and evaluation. Engineers can assess the reliability of the results and make well-informed technical decisions by asking targeted questions. By understanding result representation, meshing, modeling, and the limitations of simulations, engineers are able to pose deeper and more focused questions. This enables them to better evaluate the quality and reliability of FEM analyses and make sound technical decisions.

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