Non-destructive Testing Of Composite Panel Internal Defect

In recent years, the conflict between timber supply and demand became more and more serious; the shortage of wood resources has become a bottleneck in China’s forestry industry. Chinese researchers faced a pressing question is how to use resources rationally and save them. Wood composite material is a kind of eco-friendly materials, which is made from wood. It can realize the efficient utilization of wood resources and it provides a new way to ease the strain on the resources and protect the environment. The purpose of this research project is to find an effective non-destructive testing methods for accurately and quickly determining a variety of information within the composite panel, without damaging the original structure of the composite panels, and, to identify various defects that affect the processing of composite panels.Firstly, this paper did research on X-ray detection method that was commonly used in the nondestructive testing for wood composite board, and expounded the basic principle and system composition of this detection. According to different data acquisition and processing means, the methods of detection were divided into two parts, one was X-ray transmission detection and the other was Computerized Tomography (CT).By applying the Computerized Tomography (CT) to test a variety of Density Boards, and obtain their CT value data. Then we established the mathematical model of CT value-density for the Density Board through the result of their physical density measurement. Hence, using CT technology to measure the wood composites density was realized.Secondly, we applied the X-ray non-destructive detection method to test composite panels and obtain X-ray images of their internal defects, and then the digital image processing technology was used to image processing and analysis. First, we used the histogram gradation transformation and filtering processing on the image preprocessing to improve the image quality, highlight the target. Thereby, the effects of image segmentation and defect detection were ensured. Then we showed a variety of image defect detection methods, there were the classic gray threshold segmentation method, several image edge detection operators, more advanced edge detection method based on multi-fractal theory and a mathematical morphology processing technology. And information entropy theory is also applied to the detection of defects in composite panels. Based on these methods of non-destructive testing technology and analytical processing, we made defect details in the composite plate to be more obvious and easier for human eye recognition and computer analysis.In this paper, we gave a mathematical model for several types of defects. Then based on some image processing technologies such as minimum-perimeter polygon approximation and Hough transform, combined with data analysis and computer graphics, we designed a set of methods that were used to process, analyze and extract the internal defects of composite panels. And the purposes of identifying, describing and redrawing the internal defects of composite panels were reached.By analyzing and processing the experimental samples of density board, plywood and blockboard, the results showed that these methods could effectively detect internal defects of composite panels. Hence, it could provide effective help to optimize the production and processing of composite panels in the future. Finally, we will ensure the reasonable wood selection and timber utilization, saving timber resources effectively, and reach the goal of sustainable development of forest ecological environment.