Study On The Detection Method Of Mesoscopic Crack Propagation In The Drying Process Of Larix Gmelinii

Wood drying stress is the main cause of cracking,warping and shrinkage in wood drying process.The study of drying stress can not only reveal the physical essence of wood drying and enrich the theory of wood drying,but also provide theoretical basis for formulating wood drying criteria and technical measures to reduce wood drying stress.At present,there are few studies on the measurement of drying stress at meso-scale and the release process of drying stress under the control of drying parameters.Based on the above problems,this paper makes a preliminary study on the detection method of microcracks caused by drying stress in drying process.The main research work is as follows:According to the requirement of microscopic observation of wood drying surface,the overall scheme of wood drying micro-crack propagation system was designed,and the image acquisition system of wood surface micro-crack was built.By reforming the traditional hot air drying chamber and setting a table in the observation hole above the chamber,the contradiction between the drying temperature of the specimen and the normal operation of the microscope directly placed in the drying chamber was solved.The common resin on the surface of larch was removed by soaking and cleaning with sodium palmitate solution,which facilitated the microscopic observation and provided experimental conditions for the study of wood drying microcrack detection methods.The extraction and processing of micro-crack image in drying process were studied.By graying the crack image,the storage space occupied by the image is saved.By median filtering,histogram equalization and image sharpening,the contrast of the image is improved and the useful information of the crack image is enhanced.Ostu and other threshold segmentation methods are used to extract the crack area with low gray value.Then the noise points in the binary image are filtered by morphological open-close operation.Finally,the equivalent area and length of the crack area in the binary image are obtained by using the pixel point method and chain code method.The size information of cracks can be calculated by calibrated pixels,which provides an effective method for quantifying crack data in drying experiments.Drying experiments under constant temperature and drying experiments under drying control parameters were carried out respectively.The microcracks that change with time during drying process were detected.From the experimental results,the microcracks detection method based on image processing technology can digitally express the occurrence of microcracks on the surface of Larch during drying process and the propagation of drying cracks under drying control parameters.The exhibition process provides an effective technical means for the fine control of wood drying.Drying experiments under constant temperature and adjusting drying parameters were carried out to detect the length of microcracks varying with time during drying.The experimental results show that the method based on image processing technology can effectively digitally represent the development of micro-crack length on larch surface during drying process.The change of crack propagation process was detected by changing drying parameters in the experiment,which provided experimental basis for fine control of wood drying.