Loading...

A Criterion for Detection of Delamination in Laminated Composite Beams and Plates Based on Modal Analysis of Damaged Structure

Kazemi Bazardehi, Roohollah | 2012

465 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42792 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Kouchakzadeh, Mohammad Ali
  7. Abstract:
  8. In this study, irregularities of the mode shapes are utilized to determine the delamination situation in a composite laminated beam. Modal analysis is used to obtain the mode shapes of the beam; afterwards, the mode shapes are filtered to extract their irregularities. Presence of any delamination and its situation (number, size and location along the length and thickness of the beam) affects the extracted irregularities. Here, detection of delamination is based on these irregularities of the mode shapes. One of the most important advantages of this method is that unlike many other similar methods, in many cases, the mode shapes of damaged structure are sufficient and the exact mode shapes of the intact structure are not required. In a delaminated beam, despite the constant time frequency through the beam, the spatial frequency of the delaminated part is higher than the other part. Utilizing a filter, the higher spatial frequency of the damaged part can be amplified. So, due to highlighted difference between two parts after filtering, one can recognize the damaged part. In real cases the experimental mode shapes are needed to judge about the damage situation; however to validate and show the ability of the method to determine the delamination situation, in addition the experimental mode shapes, the analytical and numerical mode shapes can be utilized. So, the method is validated utilizing the analytical, numerical and experimental data for different cases of beams with known delamination. As it will be illustrated, the method can be applied to obtain a reasonable approximation on the presence of delamination, its size, its location along the length, and number of delaminations for various boundary conditions. This method lacks the ability to locate the position of delamination through the thickness and the delamination should not be too close to the ends of the beam. When the analytical and numerical mode shapes are used in this method, the frequency separation is suitable but when the experimental mode shapes are used, due to noises, the spatial frequency separation is not perfect. To reduce the disturbing effects of the noises, we can use the higher order mode shapes to deduce the cut off spatial frequency. Also, considering the summation of normalized irregularities of the higher order mode shapes can be useful to detect the delamination. In the next section of the thesis, we try to figure out the situation of delamination in plates utilizing numerical and analytical mode shapes. Here, in addition to the direct utilization of the irregularity method, two new indicators named “Slope of the Smooth Part (SSP)” and “Irregularities in the Slope of the Smooth Part (ISSP)” are introduced to increase the clarity of detected damage and reduce the noisy effects. The SSP is obtained by differentiating the smooth part of the mode shape, and the ISSP is obtained by applying the filter on the SSP for another time. Using this method and the mentioned indicators, delaminations may be detected in the plates using the data of just the damaged structure. This is considered as an important advantage of the method as we do not need the intact structure data. The method is validated utilizing the numerical data for a delaminated plate model.

  9. Keywords:
  10. Lamination ; Plate ; Mode Shapes ; Composite Beam ; Filters

 Digital Object List

 Bookmark

No TOC