Author: Mitali G. Shah

Publisher:

Published: 2005

Total Pages: 354

ISBN-13:

"The enormous potential that the composite materials can offer to civil infrastructure, mechanical and aerospace industries, and many other sectors has been hindered due to the lack of reliable Structural Health Monitoring (SHM) system capable of detecting damage occurrence and predicting its related effect. Implementation of SHM techniques could substantially reduce the maintenance cost and minimize the likelihood of catastrophic failure of the structures. The main objective of this study is to evaluate the dynamics-based damage detection techniques for the beam-type composite structures using smart piezoelectric materials and modern instrumentation like Scanning Laser Vibrometer (SLV). The study comprises of testing six E-glass/epoxy composite beams with different damage configurations (i.e., delamination, saw-cut and impact damage) using two different sensor systems: (1) Polyvinylidenefluoride (PVDF) sensors and PZT (lead-zirconate-titanate) actuator patches, and (2) SLV system. The experimental tests are conducted using the two sensor systems, and the numerical finite element (FE) analysis is also performed to complement the damage detection. Eight different damage detection algorithms (i.e. absolute difference method (ADM), Damage Factor Method (DFM), Modified Damage Factor Method (MDFM), Damage Index Method (DIM), Uniform Load Surface (ULS), Gapped Smoothing Method (GSM), Strain Energy Method (SEM) and Generalized Fractal Dimension (GFD)) are employed to analyze the experimental and numerical data. Of the eight algorithms, the GSM, SEM and GFD using the ULS curvature mode shapes are emphasized, and a combined static-dynamic approach is further used to magnify the effect of damage. From the damage detection outcomes, it is observed that the PVDF sensor system in which the curvature mode shapes are directly acquired exhibited good sensitivity to damage and could locate damage accurately; while the SLV system proved to be more convenient and effective, and it was capable of scanning large number of points over the entire beam specimens. The damage detection algorithms like the GSM, SEM and GFD based on the utilization of ULS curvatures successfully identified the presence and location of damage without considering the data from the healthy beams as the reference. The GFD provided fairly good results; however, it showed extra peaks at locations other than the actual damage location. The employment of the static-dynamic approach apparently increased the effect of damage (e.g., the delamination), and the application of GSM, GFD and SEM further facilitated to quantify the magnifying effect. In conclusion, dynamic response measurement using two proposed sensor systems and related modal analysis and damage evaluation are demonstrated in this study. The successful implementation of the damage detection techniques, such as GSM, GFD, SEM and combined static-dynamic approach, validates the effectiveness and accuracy of the two sensor systems in damage detection, and they can be integrated with SHM application."--P. iii-iv.