外力作用下竹材不同尺度的断裂行为及机制

doi:10.11707/j.1001-7488.LYKX20220116

摘要/Abstract

摘要：

目的: 聚焦于探究在顺纹劈裂和径向横纹压缩力作用下，竹材在宏观、组织和细胞等不同尺度的断裂行为，剖析外力作用下竹材断裂机制，为竹材新技术、新工艺、新产品开发提供理论依据。方法: 以毛竹为研究对象，对其施加顺纹劈裂和径向横纹压缩作用，利用场发射扫描电镜（FESEM）观察维管束和薄壁组织及导管、纤维和薄壁细胞的断裂形貌和裂纹扩展路径，结合纳米压痕仪测量纤维和薄壁细胞2类细胞壁的微观力学强度，探索竹材在顺纹劈裂和径向横纹压缩力作用下不同尺度的断裂破坏特性。结果: 竹材在顺纹劈裂力作用下，宏观上呈顺纹劈裂破坏，断裂形貌近乎为直线状；在组织层面，维管束中纤维鞘和薄壁组织中沿顺纹劈裂，维管束中导管的细胞壁呈撕裂破坏；在细胞层面，纤维和大部分薄壁细胞为胞间层破坏，有少数薄壁短细胞的细胞壁被撕裂。竹材在径向横纹压缩力作用下，宏观上呈压溃破坏，在顺纹方向形成系列不规则裂纹；在组织层面，维管束受到明显破坏，纤维鞘中形成不规则裂纹，导管的细胞壁被压溃，薄壁组织呈阶梯状分层破坏；在细胞层面，与顺纹劈裂力的破坏模式相似，纤维和大部分薄壁细胞为胞间层破坏，不同的是裂纹在部分薄壁短细胞交接处会发生转向，沿径向拓展，使断裂面呈阶梯状。竹材纳米压痕结果显示，纤维和薄壁细胞的胞间层硬度和模量均低于次生细胞壁。结论: 竹材在不同外力作用下，其宏观破坏行为不同，在顺纹劈裂力作用下呈顺纹劈裂破坏，在径向横纹压缩力作用下呈压溃破坏，但在细胞层面上无论纤维还是薄壁细胞均以胞间层撕裂破坏为主。裂纹在纤维和薄壁细胞的胞间层产生，并沿细胞之间界面的横向和纵向传播，使纤维细胞剥离，纤维鞘被分散成纤维束，薄壁细胞脱落，薄壁组织分层。结合纤维和薄壁细胞壁层的微观力学性能发现，由于胞间层的微观力学强度小于细胞壁层，顺纹劈裂和径向横纹压缩作用引起的胞间层断裂及裂纹在横向和纵向的传播，能实现纤维和薄壁细胞分离。

关键词: 竹材, 断裂, 劈裂力, 压缩力, 微力学性能

Abstract:

Objective: The purpose of this study was to investigate the crack behavior and mechanism of gradient structure in bamboo under grain splitting and radial compression to provide a theoretical basis for the application in engineering materials. Method: The external force of grain splitting and radial compression were applied on bamboo to induce initial crack. Field emission scanning electron microscope (FESEM) was conducted to observe the fracture appearance and crack propagation in vascular bundles, parenchyma and cells along the transverse and longitudinal direction. Micro-mechanical properties of fibers and parenchymal cells wall were measured to further illustrate the fracture mechanism stemming out from the bamboo’s hierarchical configuration. Result: The FESEM results were as follows: grain splitting-induced cracks appeared and grew in the middle lamellae (ML) of fiber and parenchymal cells along the transverse and longitudinal direction, which resulted in the transverse tearing of vascular bundles and parenchyma. Radial compression-induced cracks also appeared and grew in the middle lamellae (ML) of fiber and parenchymal cells along the transverse and longitudinal direction. In the transverse direction, dendritic cracks occurred on the surface of the fibrous sheath and make the vascular bundles disperse into fibrous bundles. In the longitudinal direction, fibers separated and parenchymal cells exfoliated. The nanoindentation results showed that the indentation modulus and hardness of middle lamellae were lower than that of cell wall layer in fiber and parenchymal cells, which was prone to fracture. Conclusion: In this study, by observing the fracture morphology and crack propagation path of vascular bundles and parenchyma under grain splitting and radial compression, it was found that the vascular bundles split into fiber bundles and interlaminar fracture occurred in the parenchyma. It was found that the fiber and parenchymal cells could be separated by the transverse and longitudinal fracture of the middle lamellae (ML) under the grain splitting and radial compression because of the lower mechanical strength.

Key words: bamboo, fracture, splitting force, radial compression force, micro-mechanical properties

中图分类号:

TB301

郝秀,李澍农,杨春梅,于文吉,余养伦. 外力作用下竹材不同尺度的断裂行为及机制[J]. 林业科学, 2023, 59(11): 118-123.

Xiu Hao,Shunong Li,Chunmei Yang,Wenji Yu,Yanglun Yu. Crack Behavior and Mechanism of Gradient Structure in Bamboo under Grain Splitting and Radial Compression[J]. Scientia Silvae Sinicae, 2023, 59(11): 118-123.

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