基于弯曲挺度法的缠绕用薄竹篾柔性表征

利用竹材的高柔性制造的竹缠绕复合材料是竹材创新利用的革命性产品。深入研究竹材柔性表征方法、评价指标和内在机理可为定向仿生制备高性能竹缠绕复合材料和优化竹缠绕管道工艺提供理论指导。探索弯曲挺度法表征缠绕用薄竹篾柔性的适用性,比较竹材维管束梯度结构和木材木射线组织微观结构差异对竹、木材柔性的影响机制。结果表明:弯曲挺度法适用于缠绕用薄竹篾的柔性表征,该法可快速、准确地获得不同竹篾薄层的柔度。适宜的测试条件为:跨厚比不小于100,加载角速率为600~1800(°)/min。竹材柔性具有梯度性:从竹黄到竹青,随着纤维比量增加,竹篾(50 mm×5 mm×1 mm)柔度从2.92×10-3 mN-1·m-1降低至1.07×10-3 mN-1·m-1,竹材柔性降低。利用混合定律获得竹材维管束和薄壁细胞的弯曲模量和柔度(厚1 mm)理论值分别为0.365 GPa、28.82 GPa和3.284×10-2 mN-1·m-1、0.42×10-3 mN-1·m-1。在相同含水率、尺寸和密度下,竹、木材比柔度排序为竹黄侧>竹青侧>木材,木材柔性低是横向木射线组织限制其柔性变形所引起的。

Flexibility characterization of bamboo slivers through winding-based bending stiffenss method

Bamboo-based winding composites(BWCs)made of bamboo with high flexibility are the revolutionary products for the innovative utilization in the forestry industry in China.In-depth study of the characterization methods of bamboo flexibility,evaluation indicators and internal mechanisms can provide theoretical guidance for the directional bionic preparation of high-performance bamboo-based winding composites and optimization of the winding process.The bending stiffenss method was used to characterize the flexibility of bamboo slivers,which can compare test conditions,such as loading angular rate(ω)and span thickness ratio(l/h),and the influence mechanism on the flexibility,between bamboo gradient structure of vascular bundles and wood ray microstructure.The results showed that the bending stiffenss method was suitable for the flexible characterization of bamboo slivers.This method could quickly and accurately examine the bamboo flexibility of different layers.The test conditions were l/h≥100 andωwas 600-1800(°)/min.The flexibility of bamboo had properties of gradient flexibility:from inner to outer parts,the flexibility of bamboo decreased as the fiber ratio increased.The theoretical values of flexural modulus and flexibility(thickness of 1 mm)of vascular bundles and parenchyma cells obtained by the mixing law were 0.365 GPa,28.82 GPa and 3.284×10-2 mN-1·m-1,0.42×10-3 mN-1·m-1,respectively.The flexible slivers prepared from the bamboo inner layer were used to wind to the inner layers of the BWCs,while the rigid bamboo outer layer was used to wind the outer layer of the pipe.This combination of soft inner and rigid outer layers helped to prepare wood plastic composites and optimize the processing of the pipe structure with its structural bionics purposes.Under the same water content,size and density,the order of specific flexibility of bamboo and wood was:bamboo inner layer>bamboo outer layer>wood.The low flexibility of wood was caused because its flexible deformation was limited by the lateral wood ray tissues.This advantage means that bamboo is one of the alternatives to wood for the preparation of BWCs and the range of bamboo utilization can be extended.