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Certain applications have recently appeared in industry where a traditional bar code printed on a label will not survive because the item to be tracked has to be exposed to harsh environments. Laser direct-part marking is a manufacturing process used to create permanent marks on a substrate that could help to alleviate this problem. In this research, a 532 nm laser was utilized to create a direct-part marked Data Matrix symbol onto carbon steel substrates with different carbon content. The quality of the laser marked Data Matrix symbol was then evaluated according to the criteria outlined in the ISO/IEC 16022 bar code technology specification for Data Matrix. Several experiments were conducted to explore the effects that different parameters have on the quality of the laser direct-part marked symbols. First, an experiment was conducted to investigate the effect of two different laser tool path patterns. In later experiments, parameters such as type of carbon steel, percent of laser tool path overlap, profile speed, average power and frequency were found to have significant effects on the quality of laser direct-part marked Data Matrix symbols. The analysis of the results indicated that contrast and print growth were the critical standard performance measures that limited laser direct-part marked Data Matrix symbols from achieving a higher final grade. No significant effects were found with respect to other standard performance measures (i.e., encode, axial uniformity, and unused error correction). Next, the experimental data collected for contrast and print growth was utilized as training, validation and testing data sets in the modeling of artificial neural networks for the laser direct-part marking process. Two performance measures (i.e., mean squared error and correlation coefficient) were employed to assess the performance of the artificial neural network models. Single-output artificial neural network models corresponding to a specific performance measure were found to have good learning and predicting capabilities. The single-output artificial neural network models were compared to equivalent multiple linear regression models for validation purposes. The prediction capability of the single-output artificial neural network models with respect to laser direct-part marking of Data Matrix symbols on carbon steel substrates was superior to that of the multiple linear regression models. / Graduation date: 2004

Laser ultrasonics can be used to nondestructively evaluate structures to determine the existence and location of surface and interior flaws. The goal of this research was to determine if laser ultrasonic techniques can be applied to the inspection of aluminum plate. titanium tubes, and large welded plate structures. The research was carried out with a Q-switched pulsed ruby laser emitting light of 694 nm wavelength. Ultrasonic waves were experimentally generated and recorded in the aluminum plate and the titanium tube. A comprehensive literature study was completed to determine if the technique can be applied to welded structures. For the two experimental cases, the ultrasonic waves were received by a piezoelectric pinducer which was located on the opposite side of the plate. and on the outside of the tube. A digital oscilloscope captured the signals from the pinducer. The signals were then analyzed to determine echo spacing and frequency content. The physical characteristics of the laser pulse such as the energy and full-width-half-height and amplitudes were measured via a photodiode system and a calorimeter. The aluminum plate confirmed that the system was functioning properly, as the ultrasonic echoes that were generated matched the expected results from previous experimentation. The titanium tube data turned out to be difficult to interpret due to the complex geometry and mode conversion. The welding research showed that ultrasound can be used to identify many types of flaws in a welded joint. Currently, few researchers have applied the laser based ultrasound to flaw detection in finished welds, although several have looked at using the laser ultrasound as an input to a control system for a weld in progress. The literature research uncovered the need for further studies on the application of laser based ultrasound to flaw detection in completed welds. / Graduation date: 1997

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