Study On The Poisson’s Ratio And Its Variation Pattern Of Bamboo

Poisson’s ratio,as an important performance parameter characterizing the elasticity of materials,is of great significance to the processing of materials and the stiffness and stability of their finished products.The systematic scientific study of Poisson’s ratio of bamboo provides important theoretical data for the research and development of bamboo composites with special functions,especially considering Poisson’s effect,and is of great importance to promote the development of the scientific and theoretical system of bamboo in China.In this thesis,the Poisson’s ratio of Moso bamboo was studied by electrostatic resistance strain meter and Nanoindentation tester at different growth height,age and radial part of bamboo wall,and the variation pattern of Poisson’s ratio of Moso bamboo was analyzed.Also,the structural characteristics,such as density,crystallinity,content of three elements and microfilament angle,and were analyzed by modern analytical methods,and their influence on Poisson’s ratio and the internal relationship between structural characteristics and Poisson’s ratio were discussed.The main conclusions are as follows.(1)The macroscopic Poisson’s ratio of Moso bamboo with different bamboo ages,different growth height and different radial parts of the bamboo wall was measured by electrical measurement,and its variation law was analyzed.The results showed that the maximum value of Poisson’s ratio was0.334 at 1.5m near bamboo outer layer of 2-year-old bamboo,and the minimum value of Poisson’s ratio was 0.180 at 5.5m near bamboo inner layer of 6-year-old bamboo;The Poisson’s ratio showed a decreasing trend with the increase of bamboo age,a decreasing trend with the increase of growth height,and a decreasing trend from near bamboo outer layer to bamboo inner layer in the radial direction;The correlation analysis showed that there was a negative correlation between Poisson’s ratio and bamboo age and growth height,but the correlation degree was weak;The radial part of bamboo wall had a negative correlation with Poisson’s ratio,and the correlation degree was medium;The regression analysis showed that the growth height,the radial part of bamboo wall and bamboo age were all important factors affecting the Poisson’s ratio of bamboo,and the correlation degree of the radial part was the highest,and the linear regression equation established by the three had a high degree of fitting.(2)The Nanoindentation technique was used to measure the Poisson’s ratio of bamboo cell wall at different bamboo ages,different growth height and different radial parts of the bamboo wall,and to analyze its change law,so as to explore the correlation between the Poisson’s ratio of bamboo cell wall and the macro Poisson’s ratio.The results showed that Nanoindentation technique was feasible in the measurement of Poisson’s ratio of bamboo cell wall,and the dot position should be in S2 layer of cell wall;The Poisson’s ratio of bamboo cell wall was 0.288～0.347,and in the same part of bamboo,the Poisson’s ratio of bamboo cell wall was greater than its macro Poisson’s ratio;With the increase of bamboo age,the decrease of bamboo axial stiffness is greater than that of bamboo transverse stiffness,which makes the Poisson’s ratio of bamboo cell wall decrease with the increase of bamboo age;With the increase of bamboo growth height,the increase of bamboo axial stiffness is slightly smaller than that of bamboo transverse stiffness,which makes the Poisson’s ratio of bamboo cell wall decrease with the increase of bamboo growth height;From near bamboo green to near bamboo yellow,the decrease of axial stiffness of bamboo is higher than that of lateral stiffness,which makes the Poisson’s ratio of bamboo cell wall decrease from near bamboo green to near bamboo yellow along the radial direction.(3)Modern analytical methods were used to test and analyze the influence of different factors on Poisson’s ratio and their internal connection.The results showed that: density of bamboo was positively correlated with Poisson’s ratio;cellulose content was positively correlated with Poisson’s ratio,lignin content was negatively correlated with Poisson’s ratio and hemicellulose content was not significantly correlated with Poisson’s ratio,this is due to the fact that cellulose and lignin affect the axial strain and transverse strain of bamboo respectively;crystallinity influenced Poisson’s ratio by affecting the axial strain of bamboo;microfibril angle(MFA)was positively correlated with Poisson’s ratio,and the correlation was strong.