Study On Fault Reconstruction For Wood Defects Based On Cell-based Backprojection

With the continuous development and progress at home and abroad nondestructive testing technology, non-destructive testing technology is based on the stress wave wood more and more attention of researchers, its portability, low environmental requirements for measuring, testing process is simple, without prejudice to the health detection, and you can get the desired results, etc. advantage in a short time; therefore the use of stress wave technology to detect internal defects of wood defect reconstruction has very broad prospects.Many researchers around the world study the physical characteristics of wood stress wave detection and prove that wood are natural polymer materials, it has complex structure, anisotropy and non-uniform features. Even the material properties of the same species in different growth environment are different ether. Stress wave traveling in the living trees belongs to the category of elastic waves; its law is in line with the wave equation.This paper studies the reconstruction of wood defect fault. Based on the fluctuation theory, it studies the variation of wave resistance at the interface of different media by stress wave traveling in the radial and tangential woods, and. It shows, if the stress wave travels through defect site, since wave resistance increasing leads to stress wave amplitude decreasing, it determines that the wood has interior defects, thus it proves the feasibility of the wood defect detection of the stress wave. On the basis, firstly, we make a model of cell-based backprojection making use of the time, distance and speed which stress wave travels in the wood. Then we select 6 stress wave transmitting terminals on a cavity defective hard basswood sample, we measure the time it travels by subtle instrument in normal condition, construct quality numerical model by cell backprojection model, and equivalent to a two-dimensional image pixel gray value by speed of each cell unit value, achieve fault reconstruction by MATLAB programming. And then we compare reconstructed two-dimensional defect graphics with test samples, analyze the error rate and the goodness of fit by fault reconstructing under the number of different test points, different cell densities, different moisture content, then confirm the feasibility of the algorithm. Finally, we smooth the reconstructing image by morphology, analyze the selection criteria of shape and size of the different structural elements, then we get more accurate tomographic reconstructing image.Compare with Algebraic Reconstruction Technique (ART) and the Simultaneous Iterative Reconstruction algorithm (SIRT), reconstruction based on the wood defects of cell back-projection reconstruction has the advantage of speed calculation. Therefore, the reconstruction algorithm in this paper is particularly suitable for weak data computing data of processing embedded processors, and it provides a chance to develop the portable nondestructive testing instrument of stress wave.