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 thick-walled cylinder fabricated by Laser Powder Bed Fusion (LPBF) additive manufacturing from AlSi10Mg aluminum alloy. 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 23,014 quadratic hexahedral elements (105,109 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 a 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.