Application of Laser Scannung Thermography and Regression Analysis to Determine Characteristics of Defects in Polymer Composite Materials

The method of laser point scanning thermography is highly sensitive and allows for reliable detection of surface and subsurface defects in products made of polymer composite materials. When implementing this method, the use of robotic manipulators as a scanning device makes it possible to inspect small-sized curved surface objects or to further examine questionable areas identified by other methods. The article provides information about the layout of a robotic complex for laser scanning thermography based on a five-axis robotic manipulator, laser power up to 3 W and wavelength 405 nm, as well as a COX CG640 thermal imager. A technique for processing experimental data has been proposed and regression models have been developed to make it possible to measure the size of defects along the trajectory and determine their location. To test the protocol, a control sample was made from fiberglass laminate, including artificial defects of the “delamination” type, in the form of squares of various sizes. The coefficient of determination R² of regression models turned out to be no worse than 0.94, the root mean square error of the defect model and the transverse size were no worse than 0.2 and 1.5 mm², respectively.