Study On The Bending Ductility Of Moso Bamboo

The ductility of materials refers to the deformation ability of material structure or the structural part that is selected beyond the elastic limit,without apparent stiffness or strength degradation.In this paper,the 4-year-old Moso bamboo(Phyllostachys edulis(Carr.)J.Houz)was selected to conduct a study on its bending ductility at cellular level.The morphology of the bamboo cells during bending tests was investigated by in situ electron microscopy,X-ray microscopy and environmental scanning electron microscopy.The morphological changes of the vessel,fibers,and parenchyma cells and their mechanical response were studied.The contribution of the vessel,fiber and parenchyma cells and the vascular bundle content to the ductility of the bamboo was analyzed.The mode of destruction and synergistic effect of different cells during the interactive loading process was systematically explored.This paper revealed the reasons for the good ductility of bamboo from the cellular level.The main conclusions of the study are as follows:(1)The ductility of bamboo can be represented by ductility coefficient and relative curvature which are positively correlated with each other.Image-Pro Plus can be used to study the deformation of bamboo cells directly.(2)Influences of vessels on bending ductility of bambooThe bending ductility of bamboo can be improved by the vessel with large apertures in the compression layer.The vessel recovered after unloading.The recovery and deformation in the length direction was bigger than that in the width direction.The recovery of vessels in different locations was that: macro recovery> length recovery > width recovery.The recovery of vessel was poor.The failure mode of vessel was divided into two types: perforation the pits on the vessel and near the pits on the vessel.(3)Influences of fibers on bending ductility of bambooDuring the process of interactive loading,the distribution of fiber affected the ductility of bamboo.When the distribution of fiber was in pattern of P-F-P(parenchyma cell/ fiber/ parenchyma cell),the ductility of bamboo was the best.When the distribution mode of bamboo fiber was in pattern of F-P-F,the ductility of bamboo was worse with higher fiber content.Fiber breakage had a significant impact on the recovery of bamboo.Overall,the recovery of the width of the fiber is less than that of the sample,indicating that the interface between fiber layers decreased the recovery of sample.The fiber in the compression layer was destroyed by extrusion,stretching and delamination devastation;the fiber damage mode in mesne layer and tensile layer was similar.They had two forms: smooth fracture and multi-level delamination.During the process of bending,the fibers first slip-delaminated and then ruptured.The destruction in fibers happened earlier than that in parenchyma cells.(4)Influences of parenchyma cells on bending ductility of bambooParenchyma cells recovered after unloading and had good ability of stretching and compressing which could contribute to large bending deformation without damage and improve the ductility of bamboo.The recovery of parenchyma cells in different locations was that: length recovery> macro recovery> width recovery.Parenchyma cells had a positive contribution to the ductility of bamboo in the length direction.From morphological parameters,the morphological changes of the long and short parenchyma cells in the same tensile layer were the same.However,the long parenchyma cells had larger length strain.The parenchyma in the tensile layer had plastic deformation in the late stage,while the parenchyma cells showed elastic deformation before destruction.The parenchyma cells had good elasticity.In the interactive loading test,the recovery was that: parenchyma cell> parenchyma> macro sample.The interface between parenchyma cells and the interface between the different tissues reduced the recovery of the bamboo and improved the ductility of the bamboo.Cracks extend along pits in parenchyma cells.The multi-layer cell wall structure of parenchyma cells hindered the propagation of cracks and sample destruction,and improved the ductility of bamboo.(5)Influences of vascular bundle content on bending ductility of bambooBamboo sliver sample with higher vascular bundle content had higher bending strength,bigger elastic deformation,smaller ductility,and higher recovery.The parenchyma cell of bamboo(at the outer side)in the compression layer were both compressed in the length and width directions.The parenchyma cell at bamboo(on the inner side)in the compression layer were compressed in the length direction and stretched in the width direction,respectively.The interface between the parenchyma cells decreased the recovery of the bamboo;the interface between the fiber and the parenchyma decreased the recovery of the bamboo.(6)The vessel,fiber and parenchyma cells had a good synergistic mechanism.When the sample was bending,the vessel with big hole and parenchyma cell with good elasticity can provide space for the deformation of fibers and support fiber having a stronger ability to deform.The pits in the vessel and parenchyma cells can relieve the stress which was benefit for large deformation of bamboo.This synergistic reaction can improve the ductility of bamboo.Bamboo has good ductility which not only comes from its behavior of vessel,fiber,and parenchyma cells,but also their reasonable distribution and synergistic mechanism.Further study on the ductility of bamboo would not only reveal the important mechanics and material composition principles behind the high strength and toughness of bamboo but also provide the scientific basis for its high value-added utilization.