Investigation of Static Load Effects on Active Vibration Based Structural Health Monitoring

Open Access
- Author:
- Long, Justin Allan
- Area of Honors:
- Aerospace Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Stephen Clarke Conlon, Thesis Supervisor
Dennis K Mclaughlin, Thesis Honors Advisor
Dr. George A Lesieutre, Faculty Reader - Keywords:
- structural
health
monitoring
static
loading
aerospace
structures
airplane
helicopter - Abstract:
- The need for improved maintenance and inspection methods for aircraft has led to an increase in the development of vibration based Structural Health Monitoring (SHM) systems. In this thesis, the single tone active interrogation Nonlinear Structural Surface Intensity (NSSI) damage detection method is used on a stiffened aluminum panel test bed, in order to establish the uncertainty of measurements and to study the effects of static loading on the damage detection technique. Optimal drive frequency and amplitude conditions (2100 Hz, 0.3 N) were selected in order to perform a baseline damage progression (34 dB detection sensitivity at the largest damage increment). Repeated measurements showed some variation, allowing the construction of confidence intervals around NSSI measurements. The largest damage increment studied was easily detected, but smaller increments were sometimes difficult to distinguish using fixed drive (interrogation) conditions. After obtaining a baseline result, static tensile and compressive loads (2 lbs., 4 lbs. and 6 lbs.) were added into the system to observe the effects on NSSI, and other detection metrics. The full 6 lb. loading caused a 14 dB decrease in NSSI detection sensitivity under tensile loading, and a 17 dB decrease under compressive loading. Frequency sensitivity and amplitude hysteresis studies were conducted in an attempt to regain lost detection strength, by re-optimizing drive conditions under the applied loads. It was found that tension and compression change the optimal active interrogation frequencies to 2200 Hz and 2300 Hz respectively, signifying that the damage “looks” smaller under applied loads. At 2100 Hz, greater force is required to trigger the nonlinear response under loading. Re-optimizing the drive conditions improved the detection sensitivity by 15 dB in the tensile case and 35 dB in the compressive case, indicating that some or all of the initially lost sensitivity due to static loading can be regained. The results suggest that the active NSSI technique could be successfully translated to real airframe structures, and maintain detection performance when these structures are subjected to static or quasistatic loading.