Detecting Material Defects Using a Scanning Laser Beam

Abstract

A moving line-source laser beam was used to scan the entire surface of a rectangular plate, pursuant to locating defects. The laser generates a point beam of laser energy, which is transformed into a line-heating source using sheet-forming optical components. The heat source is then scanned across the sample by placing the sample in a vertical position on a moving servo table, which moves horizontally at a prescribed speed. A relatively small overall temperature rise of 10° is desired to allow the heat transfer to be modeled mathematically assuming constant thermal properties. A thermal camera was employed for recording the temperature distribution on the nonheated side of the sample. Once a mathematical model or other smoothing technique is fitted to the experimental data, the calculated temperature is subtracted from the measured temperature, and a residual temperature field is created. Additional features of this research include the use of simple spline fits, Bayesian techniques, and the mollification method. The results are provided, which allow for a comparison of the effectiveness of each technique.