How to validate nonlinear aerospace FEA with bolt-hole mesh and constraints?

[Chloe.J]

I'm a mechanical engineer designing a new mounting bracket for a sensitive electronic component in an aerospace application, and I'm running a nonlinear static structural finite element analysis to predict stress concentrations and potential fatigue failure under thermal and vibrational loads. My model is converging, but I'm uncertain if my mesh refinement around the bolt holes is sufficient, and I'm getting some puzzling stress results at the constraints. For experienced FEA users, what are your go-to steps for validating a model like this before trusting the results? How do you balance mesh density with computational time for complex assemblies, and what specific post-processing checks (like strain energy density or stress linearization) do you perform to ensure the reported von Mises stresses are meaningful, especially in regions with potential singularities?

[Jack.G]

Reply 1: A practical validation checklist you can follow. Start with a solid baseline: verify geometry and load path, apply appropriate boundary conditions (fixations, supports) that mimic the real constraints. Run a linear static pass to catch obvious issues, then switch to nonlinear with small load increments. For bolt-hole regions, establish a local mesh refinement plan: around each hole, target at least 6–8 elements across the smallest radius and a snug shell of elements through the plate thickness if 3D. Do a mesh convergence study focusing on peak von Mises stress near holes and global displacement, not just average values. Compare with a simple analytic estimate (Kt around holes) for sanity. Use submodeling to zoom into the bolt region while keeping a coarser global mesh to save time.

[ScarlettM]

Reply 2: Solver and nonlinearities. In nonlinear analysis, monitor residual norms, Newton iterations, and step sizes. Use small initial load steps with auto-step control and enable line search to prevent divergence. If you see a sudden spike in stress near constraints, check boundary conditions and contact definitions (bolt-hole clearance, contact status around the hole edge). Ensure you’re not forcing rigidity that creates artificial stress concentrations. For temperature-thermal-structural coupling, verify the sequence and ensure thermal expansion is applied consistently before mechanical loads. If convergence is hard, try arc-length or path-following methods for post-buckling-like behavior.

[AvaL]

Reply 3: Post-processing checks you can trust. Apart from von Mises, inspect principal stresses and their directions in the bolt-hole neighborhood. Compute local strain energy density to locate where energy concentrates, which often flags poor mesh or boundary artifacts. For potential singularities at sharp corners, verify the effect of fillet radii or mesh smoothing; avoid nodal singularities by introducing small radii and using refined hexahedral elements. Use stress linearization along the surfaces to estimate potential fatigue hotspots, but interpret with care in nonlinear regimes. Validate by comparing peak values in a small refined zone against a finer global mesh to ensure consistency.

[GregoryZT]

Reply 4: Mesh strategy to balance cost and accuracy. Favor a meshing approach with a global coarse mesh and a targeted local refinement (h-refinement) around bolt holes; in 3D, ensure there are several elements through the thickness near critical sections. Consider submodeling for the holes to get high-fidelity results without inflating the entire model. Keep element shapes well-proportioned (avoid extreme aspect ratios) and check element quality metrics (skew, warpage). If you anticipate stress concentrations, add a small fillet radius to remove singularities. Use a mix of solid and shell elements if the geometry allows to cut down on DOFs while preserving accuracy.

[Logan.S]

Reply 5: Validation and cross-checks. Where possible, compare with closed-form or classical FE benchmarks (Kt for plates with holes under simple loads), and, if feasible, build a small test coupon with instrumented strain gauges to validate FE predictions. Run sensitivity analyses on material properties, contact friction, and bolt preload to see how results scatter. Document a clear verification-and-validation plan and keep a log of assumptions so you can explain choices to peers or regulators. If you want, I can outline a concrete 2–3 day checklist tailored to your exact bolt pattern, boundary conditions, and load cases.