Study On Degradation Of Mechanical Properties Of Decay Wood

The wooden structure of ancient architecture is an important carrier of the history and culture of the Chinese nation and a rare treasure left to us by our ancestors.However,as a special kind of biomass building material,wood will be eroded by decay bacteria in the natural environment,which will cause the bearing capacity of the component to decline and the structural safety will be seriously threatened.The scientific protection of structure is of great significance.Most of the current research on wood decay is carried out from the perspective of forestry science,and most of them focus on the classification of decay fungi and the exploration of decay mechanism.The research on the changes of mechanical properties after decay is relatively insufficient.This article is devoted to studying the degradation law of the mechanical properties of wood after decay,and revealing the microscopic mechanism that causes the degradation of its mechanical properties.The main research contents and relevant conclusions are summarized as follows:(1)A 14-week laboratory accelerated brown rot test was carried out for the specimens in the wood material property test specifications(test specimens for compressive along the grain,bending,tensile,and compressive elastic modulus along the grain).The test procedure includes,the transformation of the decayed specimen simple incubator,the preparation of the vermiculite scobs culture medium,the preparation before inoculation,the whole inoculation process,etc.(2)The surface color appearance and weight loss rate of the specimen after brown rot were analyzed.After brown rot,the color of the surface of the specimen changed obviously.With the increase of decay time,the color of the surface gradually changed from light yellow to yellowish brown.The greater the degree of decay,the softer the surface of the specimens,the more serious the loss of the surface fibers,and some of the specimens even have obvious missing corners.The weight of the specimen also suffered a significant loss after brown rot.With the increase of the decay time,the rate of weight loss of the specimen is roughly increasing.(3)The brown rot treated specimens were tested for mechanical properties.The compressive strength along the grain,bending strength,and tensile strength along the grain of the red pine specimens after brown rot have a significant decrease,and the strength loss rate is positively correlated with the decay time and weight loss rate.The bending elastic modulus also decreased after decay,but the degree of decrease was lower than the bend strength.After 14 weeks of decay,the average loss rates of compressive strength along the grain,bending strength and tensile strength along the grain were 32.13%,40.81%,and 41.13%,respectively.With the increase of decay time,the degradation of compressive elastic modulus along the grain is not obvious.(4)In order to explore the micro-mechanism of the degradation of the mechanical properties of the wood after brown rot,the specimens that have undergone the wood property test were followed by scanning electron microscope observation,chemical composition analysis,and crystallinity determination.Scanning electron microscopy observations showed that the specimens with higher strength loss caused by decay were severely degraded in the cell wall,the hyphae accumulated in large amounts,and the ability of the cell wall to resist external forces decreased compared with the blank control specimens.The greater the degree of brown rot and the greater loss of strength,the lower the brown cellulose,cellulose,and hemicellulose content.After brown rot,the crystallinity of the specimen decreased,but the unit cell structure did not change,and the more strength loss,the lower the crystallinity.Studies have shown that the main reason for the decline of mechanical properties after decay is the degradation of the wood cell wall and the reduction of important chemical components that make up the cell wall.(5)The correlation between different micro indexes and strength loss was summarized.According to different mechanical properties and microscopic mechanism of decay damage,the best microscopic index was selected to establish the mathematical regression model for quantitative prediction of the strength degradation after decay,which realizes the connection between the micro mechanism and the macro mechanics.