Modal Analysis of an Additively Manufactured AlSi10Mg Thick-Walled Cylinder: Finite Element Simulation, Experimental Validation, and Non-Conservative Damping Characterization

Abstract

This paper presents a systematic experimental and computational investigation of the free-vibration characteristics of a Laser Powder Bed Fusion (LPBF) AlSi10Mg thick-walled cylinder, a geometry relevant to electric-machine housings, hydraulic sleeves, and pressure-carrying components exposed to resonance-critical service loads. The specimen has an outer diameter of 94 mm, an inner diameter of 64 mm, a wall thickness of 15 mm, and a height of 90 mm, placing it firmly in the thick-walled regime (d/D=0.68). A three-dimensional finite element model comprising 23,864 total elements (23,236 SOLID186 solid elements and 628 surface/contact elements) and 106,015 nodes was constructed in Ansys Mechanical using the AlSi10Mg material database entry (E = 75 GPa, ρ = 2670 kg/m3, ν = 0.33) and solved with the Block Lanczos eigensolver under free–free boundary conditions. Experimental modal analysis (EMA) was conducted using Brüel & Kjær software with an impact hammer with a 260-node measurement grid covering the outer surface and both end rings; frequency response functions were acquired over 0–22,500 Hz. Fourteen flexible modes were identified in simulation; nine corresponding experimental modes were resolved with frequency deviations ranging from 0.13% to 1.10%. In addition to frequency correlation, this paper introduces a non-conservative damping characterization framework comprising: (i) Rayleigh (proportional) damping coefficient extraction from EMA data and assessment of its frequency-domain validity; (ii) a viscoelastic complex-modulus model relating the real storage modulus E′ and imaginary loss modulus E″ to the modal loss factor η and damping ratio ζ; and (iii) a practical design workflow for resonance mitigation of future AM structures including electric machine frames. Experimental damping ratios (ζ=0.013–0.311%) are converted to per-mode E″ values and loss factors, revealing that energy dissipation in LPBF AlSi10Mg is strongly mode-shape-dependent and cannot be accurately represented by a single Rayleigh model.