Airframe vibration and damping characteristics: A study comparing flight structures to laboratory substructures with applications to vibration based structural health monitoring technology development

摘要

Vibration damping levels over a wide frequency band for complex built-up structures arevirtually impossible to predict. In this work, rotorcraft airframe structures were targetedfor vibration based Structural Health Monitoring (SHM) technology development andimplementation. Damping is a critical parameter for understanding the vibrationcharacteristics of a structure and realistic damping levels must be established for theapplication of relevant vibration based damage detection simulations and laboratory testbed assessments to be made. The goal of this investigation was to quantify the vibrationand damping characteristics of an actual flight system structure, compare / contrast theresults to laboratory development test structures and identify any important trends /discrepancies. Experimental modal analysis and decay techniques were applied to a UH-60Blackhawk airframe (in-flight configuration). Structural mobility, resonance frequencies,modal damping, and high frequency one third octave band decay based damping levelswere measured and quantified. Similar measurements were also made on laboratory teststructures used for technology development and verification testing. The measured (flightconfiguration) airframe damping loss factors varied from approximately 0.01 to 0.10 overthe frequency range 2 Hz to 10,000 Hz. The flight vehicle damping characteristics werecompared / contrasted with laboratory test structures, quantifying the damping effects dueto built-up structure complexity. Methods for enhancing the laboratory test structureswere also investigated showing positive results.