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 arernvirtually impossible to predict. In this work, rotorcraft airframe structures were targetedrnfor vibration based Structural Health Monitoring (SHM) technology development andrnimplementation. Damping is a critical parameter for understanding the vibrationrncharacteristics of a structure and realistic damping levels must be established for thernapplication of relevant vibration based damage detection simulations and laboratory testrnbed assessments to be made. The goal of this investigation was to quantify the vibrationrnand damping characteristics of an actual flight system structure, compare / contrast thernresults to laboratory development test structures and identify any important trends /rndiscrepancies. Experimental modal analysis and decay techniques were applied to a UH-60rnBlackhawk airframe (in-flight configuration). Structural mobility, resonance frequencies,rnmodal damping, and high frequency one third octave band decay based damping levelsrnwere measured and quantified. Similar measurements were also made on laboratory testrnstructures used for technology development and verification testing. The measured (flightrnconfiguration) airframe damping loss factors varied from approximately 0.01 to 0.10 overrnthe frequency range 2 Hz to 10,000 Hz. The flight vehicle damping characteristics wererncompared / contrasted with laboratory test structures, quantifying the damping effects duernto built-up structure complexity. Methods for enhancing the laboratory test structuresrnwere also investigated showing positive results.