Does refining the mesh of the 3D eigenbuckling check change how the closed-form bracket-arm buckling factors compare?
research/simdesign-shellconverge
Mesh refinement of the 3D eigenbuckling check of the bracket arms (stylised): refining length, width and thickness lowers every FE/closed-form ratio by 0.9–1.3 points, so the governing vertical arm agrees with the closed form to within 1% (ratio 0.99–1.00 at the finest mesh).
What it found
A stylised, preliminary mesh study of the model in simdesign-webshell. Refining the quadratic-hexahedron mesh in length, width and thickness lowers the finite-element critical load every time, by 0.9–1.3 percentage points of the closed-form value in total at web widths 8, 16 and 25 mm (2 mm gauge); thickness and width refinement dominate and length refinement contributes under 0.1 point. On the finest mesh (72×8×2) the governing vertical arm sits at 0.992, 0.996 and 1.002 of the closed form, so the two agree within about 1% and the earlier fine-mesh ratios were slightly high. The horizontal-arm closed form stays conservative (ratios 1.046, 1.135, 1.279). Only two refinement levels per direction, so no convergence rate or extrapolated limit is claimed. Simulated only.
Paper, code and results
More in Simulation-first design
- At what bar slenderness does the 3D eigenbuckling model agree with the slender-beam closed form?How the 3D eigenbuckling model compares with the slender-beam closed form as a bar gets longer (stylised): the finite-element load is 14.5%, 7.4%, 3.8% and 2.1% above it at l/w = 3, 6, 12, 24.
- How much stiffer than a uniformly thinned plate is a topology-optimised part, and how does that depend on volume fraction?How much stiffer a thresholded topology-optimised part is than a uniformly thinned plate across volume fractions (stylised): 26–31% lower compliance at v = 0.3–0.5, shrinking to 14% at 0.8, and disconnected designs below that on coarse grids.
- At what rate does the 3D eigenbuckling model converge under uniform mesh refinement?Observed convergence order of the 3D eigenbuckling model on a short bar (stylised): three uniform meshes give order ≈ 2.6 and a Richardson limit FE/closed-form ratio 1.137, so the gap to the closed form is not discretisation error.
- What does it cost to replace the w/b ≤ 8 rule of the laser-cut bracket with a buckling-factor guard?Replacing the w/b ≤ 8 slenderness rule of the laser-cut bracket with a lateral-torsional buckling factor ≥ 3 lets the optimiser use the 1.5 mm gauge at w ≈ 18.7 mm, 31.3 g instead of 35.9 g (about 12% lighter), and the guard does not bind at that optimum; the result depends on the assumed factor (no feasible design for factors ≥ 5 at that gauge); stylised, preliminary.
- When does the buckling guard of the laser-cut bracket start to bind as load and arm length change?Sweeping tip load (50–400 N) and arm length (60–120 mm) of the laser-cut bracket: the buckling-factor ≥ 3 guard binds only at 120 mm arms (unguarded optimum has factor 1.9; 69 g vs 59 g), while the old w/b ≤ 8 rule costs 14–25% in mass in five of six cases (stylised, two seeds).
- How sharp is the feasible edge of the 2 mm laser-cut bracket web at 0.1 mm resolution, and is it mesh noise?A 0.1 mm scan of the feasible edge of the gauge-2 bracket web (nine mesh/radius cases): peak stress is not monotone in w, with residual jitter of 0.9–2.4 MPa about a quadratic trend, the same size as the 0.1–1.7 MPa gap to the 100 MPa limit just below each edge, so the edge is a band of about 0.5 mm and the earlier refinement shift is not separated from mesh noise; stylised, preliminary.
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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.