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Large-Scale Cylindrical Isogrid Bay (Ø4 m): Heavy Axial Crushing with Beam Self-Contact
Geometric nonlinear arc-length buckling and beam-to-beam self-contact analysis of a 4-meter aerospace lattice interstage bay under 35 MN axial compression.
Full-scale aerospace interstage bays and diagrid space trusses (4-meter diameter, 8-meter length) carry massive launch vehicle thrust loads. When ultimate capacity is exceeded, progressive diamond-wave buckling folds adjacent ring frames together. WebCAE's spatial beam-to-beam self-contact algorithm (nlgeom beamcontact self=on) prevents interpenetration of converging ring tubes (Ø80x2 mm), capturing 24 active contact pairs during 2.28 meters of catastrophic axial contraction under 35 MN axial load.
1. Geometry & FEA Mesh
- •Full-scale cylindrical bay: diameter D = 4.0 m (R = 2.0 m), length H = 8.0 m (L/D = 2.0).
- •9 elevation rings (dz = 1.0 m), 16 sectors around circumference, 400 members subdivided into 10 elements each (4,000 beam elements, 22,464 DOFs).
- •Structural steel tubing: outer diameter 80 mm, wall thickness 2.0 mm (inner diameter 76 mm).
- •Line-to-line beam self-contact with radius ra = 40 mm, penalty = 3.5 MN/m, search radius = 200 mm.
2. Loads & Boundary Conditions
- •Bottom ring at z = 0 clamped in all degrees of freedom (ux = uy = uz = rx = ry = rz = 0).
- •Pure axial compression along Z (total load Fz = -35 MN = 16 × -2.1875 MN) applied to top ring nodes (z = H).
- •Zero lateral or radial forces; natural out-of-roundness imperfection (7.5 mm = 0.375% of radius) triggers physical buckling.
3. Simulation Results & Findings
- ✓Full arc-length convergence across 28 equilibrium increments (225 Newton iterations).
- ✓Top axial crush reaches uz = -2,275.78 mm (2.28 m contraction), peak total deflection |u| = 2,291.41 mm (2.29 m).
- ✓Opposite ring walls fold inward by 1.93 m from each side to meet at the center (y = ±70 mm) across 24 active beam self-contact pairs without interpenetration.
- ✓Fundamental natural frequency f₁ = 14.33 Hz.
Validates aerospace launch vehicle interstage capacity, emergency structural collapse limits, and beam-to-beam contact.
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