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Aerospace Mounting Bracket: Random Vibration Spectral Fatigue & 3σ Peak Stress Mapping
High-precision 7075-T6 aluminum aerospace equipment bracket subjected to wideband random base acceleration power spectral density (PSD) with Miles-equation modal synthesis and 3σ statistical stress assessment.
Avionics brackets and payload fittings on launch vehicles and aircraft undergo severe random acoustic and mechanical turbulence best characterized by acceleration spectral density (ASD, g²/Hz). In this case, an aluminum 7075-T6 bracket is subjected to a 4.36 G_rms Z-axis base vibration spectrum. WebCAE computes modal participation across 5 eigenspaces and evaluates 1σ and 3σ stress distributions for high-cycle fatigue clearance according to MIL-STD-810H.
1. Geometry & FEA Mesh
- •3D B-Rep CAD model (`aerospace_bracket.step`, 15 CAD faces, 80 × 60 × 68 mm).
- •2,299 TET4 elements, 808 nodes, 2,424 DOFs.
- •Aluminum 7075-T6: E = 71 GPa, ν = 0.33, ρ = 2,810 kg/m³, modal damping ratio ζ = 0.02 (2% critical damping).
2. Loads & Boundary Conditions
- •Mounting base flange (`surface number 29`, 80 × 60 mm) and bolt holes (`surface number 36 & 37`, Ø8 mm) rigidly constrained.
- •Z-axis random base acceleration PSD applied: [(20 Hz, 0.01 g²/Hz), (100 Hz, 0.05 g²/Hz), (1000 Hz, 0.01 g²/Hz)], yielding 4.36 G_rms overall excitation.
- •5 eigenmodes extracted and synthesized (`solve psd dir=z zeta=0.02 modes=5`).
3. Simulation Results & Findings
- ✓Fundamental resonance occurs at f₁ = 6,200 Hz with higher modes at 7,914 Hz, 8,048 Hz, 17,712 Hz, and 20,377 Hz.
- ✓1σ root-mean-square displacement is 0.090 mm; peak 3σ displacement is 0.270 mm (99.73% probability boundary).
- ✓1σ RMS von Mises stress is 0.146 MPa, scaling to a 3σ peak of 0.439 MPa at the base fillet stiffener.
WebCAE's random vibration PSD module provides aerospace payload designers with rapid certification metrics (MIL-STD-810 / NASA GEVS) directly from 3D CAD without third-party desktop licenses.
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