This report investigates the application of the guided wave non-destructive damage detection technique to pitting corrosion in aluminium beams. This method utilizes the fact that ultrasonic waves propagating along a beam will partially reflect off discontinuities along the beam (such as indented damage); this reflected wave contains information pertaining to the shape of the damage. Through the use of a laser vibrometer, the propagating vibrations can be measured and recorded. Using a computer-aided simulation program previously developed which utilizes the Timoshenko wave propagation theory, the theoretical wave propagation in specific damaged beams can be predicted. A comparison program has been developed which extracts three characteristic parameters from the measured and simulated signals (the parameters being the width ratio between the initial and reflected pulse, the height ratio between the same two pulses, and the reflection time). These values have been compared to give an indication of the level of agreement between the two signals, and hence determine the accuracy of the simulation model when applied to circular-shaped damage. To begin with, simple single-step rectangular damage cases were analysed, before moving to multiple-step damage, and finishing with a circular damage case. Additionally, when modeling single-step rectangular damage, the parameters were observed for trends while the damage dimensions were varied.
A generally good level of agreement between simulated and measured signals was obtained. For the eight single- and multiple step approximations, the maximum error in length and amplitude ratios for six of the beams was less than 11%. The two exceptions had larger errors; these can be explained, but do demonstrate some limitations of this method. The circular damage beam was modeled very well when using a three-step approximation; errors if 0.53% and 17.2% were obtained in the amplitude and width ratios respectively. The simulation model was found to be an adequately accurate method of predicting the vibrational response of an aluminium beam. On varying the damage dimensions, some complex effects were observed which would make it very difficult to predict the damage simply from the reflected signal without the use of a simulation program.
As an extension, this model was applied to a single-step damage case in a composite beam (for the purpose of investigating the possibility of future development in delamination characterization). This gave a very low level of agreement, and it was concluded that the current model cannot be used to predict longitudinal waves in composite beams.