基于同步辐射原位CT的水牛角结构性能关系研究

为探究水牛角的结构性能关系,基于上海同步辐射光源搭建了高分辨原位CT系统,对水牛角角鞘进行初始表征和准静态压缩下的实时表征,并通过Top-Hat方法提取了角鞘内孔洞三维形貌。结果显示,水牛角角鞘孔隙率在1%左右,椭圆柱状孔洞沿牛角生长方向排列成线,首尾相连却并未连通,均匀分布在波浪状片层之间。孔洞特征椭球的轴长分布满足对数正态分布,长轴和短轴的长度均值分别为7μm和3μm。原位CT结果表明,角鞘在屈服之后,初始孔洞首先扩张而形成微裂纹,随后微裂纹沿着片层界面由外向内发生桥接,片层发生局部屈曲和层间开裂,形成宏观裂纹,导致角鞘内裂纹密度急剧上升。片层之间不仅存在大量纤维黏接(提高了层间拉伸/剪切强度),而且孔洞互不连通,这些因素抑制了层间裂纹的快速传播,使得各处裂纹只能独立缓慢发展而无法贯通样品。波浪状片层使裂纹传播路径更加曲折,层间屈曲增加了片层摩擦耗能。这些机制使得牛角表现出加工硬化,也是牛角在纵向方向呈现优良韧性的主要原因。

Investigations on the structure-property relationship of buffalo horn based on in situ synchrotron CT

In order to explore the structure-property relationship of buffalo horn,a high-resolution in-situ CT system is implemented based on the Shanghai Synchrotron Radiation Source.The microstructural evolution of the buffalo horn under quasi-static compression and the initial microstructures are characterized.The three-dimensional(3D)pore networks are extracted by the Top-Hat method.The results show that the porosity rate of the horn is about 1%.Cylindroid holes are arranged in a line along the growth longitudinal direction,which are connected end to end without passage and distributed uniformly between wavy laminates.The characteristic length distributions of the pores satisfy a lognormal distribution,and the mean lengths of the major and minor axes are about 7μm and 3μm,respectively.In situ CT result shows that the initial pores begin to expand and develop into microcracks after yielding.Then,the microcracks are bridged from outward to inward along the laminate interface,followed by local buckling of laminates and interlaminar cracking,leading to macro cracks and a sharp increase in the crack density of the sample.However,there is a lot of fiber bonding between laminates which improves the interlaminar tensile/shear strength,and the tubular pores are not connected with each other,which prohibits the rapid propagation of interlaminar cracks,making cracks develop independently and slowly and unable to penetrate the sample.Meanwhile,the wavy laminates deflect the crack propagation path,and the laminar buckling increases the friction dissipation.These mechanisms have great contribution to the work hardening,leading to excellent toughness of the horn in the longitudinal direction.