Date of Award

2016

Document Type

Open Access Thesis

Department

Mechanical Engineering

Sub-Department

Aerospace Engineering

First Advisor

Victor Giurgiutiu

Abstract

Ultrasonic guided waves are very attractive for the inspection of large structures using nondestructive evaluation (NDE) and structural health monitoring (SHM) technique. Combined analytical and finite element analysis (CAFA) has been introduced for the detection of butterfly cracks in the rivet hole of the aerospace lap joint. Finite element analyses have been performed on the local damage area in spite of the whole large structure. Fundamental Lamb wave modes (S0 and A0) have been strike on the local damage from multiple directions to analyze the cracks of multiple-rivet-hole lap joint. The rivet hole cracks (damage) in the plate structure gives rise to the non-axisymmetric scattering of Lamb wave as well as shear horizontal (SH) wave although the incident Lamb wave source (primary source) is axisymmetric. Hence, the damage in the plate acts as a non-axisymmetric secondary source of Lamb wave and SH wave. The non-axisymmetric scattering of Lamb and SH waves are described using the wave damage interaction coefficient (WDIC). The WDIC of scattered Lamb and SH waves depends on the azimuth directions of the rivet hole as well as the frequencies of excitation.

The WDIC involves scattering and mode conversion of Lamb waves occurred due to local damage. WDIC is captured around the damage for each direction of incidence over the frequency domain and “scatter cube” is formed for each incident Lamb mode. By analyzing the scattered cube of WDICs over the frequency domain and azimuth directions, the optimum parameters (frequency and location of sensor) can be determined for each angle of incidence. The scatter cubes are fed into the exact analytical framework to produce the time domain signal. This analysis enables us to obtain the optimum design parameters for better detection of the cracks in the rivet holes. The optimum parameters can be obtained for all possible cases of incident Lamb waves that would help to analyze the multiple-rivet-hole problem. Some examples of obtaining the optimum parameters are illustrated based on the most prominent time domain signal. The optimum parameters provide the guideline of the design of the sensor installation to obtain the most noticeable signals that represent the presence of cracks in the rivet hole.

The thesis finishes with conclusions, and suggestions for future work.

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