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拉伸荷载条件下新型NPR锚杆韧性材料宏观变形特征分析

Macroscopic analysis of deformation characterization of a novel NPR bolt ductile material under tensile action

  • 摘要: 岩土工程在受到复杂地质条件的综合作用时极易产生大变形灾害响应,传统金属支护材料因不能够忍受大变形而发生失效破坏现象。为应对大变形灾害,研发了新型NPR锚杆韧性材料( Negative Poisson’s Ratio bolt)。为了探索新型NPR锚杆韧性材料的宏观变形特征,开展了NPR锚杆室内拉伸对比试验。采用NPR锚杆专用试验机,并利用相机进行全过程变形特征记录。结果发现:NPR锚杆具有更好的均匀变形特性,且在拉伸变形失效全过程早期阶段就开始发生均匀变形;对不同钢筋进行失效断口分类:主要分为“分层型断口”和“纤维−基体之间的界面破坏类断裂型断口”;通过力学机制分析NPR锚杆均匀变形特性及颈缩现象不显著的原因:发现NPR钢在拉伸变形失效后的颈缩处曲率半径更大,使其颈缩现象不明显,这是由于其最大均匀应变与最大应变差值相对较小所致;通过LS-DYNA算法对螺纹肋结构和光圆结构对于钢筋变形的影响进行数值模拟分析,结果证明螺纹肋结构使得钢筋在拉伸过程中能够更好地均匀变形,吸收变形能。综上所述,通过对新型NPR锚杆韧性材料的变形特征的宏观分析,有助于更好地揭示其静力拉伸性能,为准静态工程实践提供了有价值的参考。

     

    Abstract: According to the research, geotechnical engineering is easy to produce large deformation disasters when subjected to complex geological conditions, and the conventional support materials are unable to tolerate the large deformation and failure damage occurs. To cope with the large deformation disaster, the author’s team developed a novel ductile material NPR (Negative Poisson’s ratio) bolt. In this paper, in order to explore the macroscopic deformation characteristics of the novel ductile material NPR bolts, indoor tensile comparison experiments of NPR bolts were carried out. The experiment adopts a universal testing machine for NPR bolts, and utilizes a camera to record the deformation characteristic of the whole process. The experimental results found that: NPR bolts have better uniform deformation characteristics, and uniform deformation begins to occur in the early stage of the whole process of tensile deformation failure; The failure fractures classification of different steel bars, which were mainly divided into “delamination-type fracture surfaces” and “fracture-type fracture surfaces” where the interface between the fibers and the matrix breaks down; Analyzing the uniform deformation characteristics of the NPR anchors through the mechanical mechanisms and the reason for the insignificant necking phenomenon: it is found that the radius of curvature of NPR steel is larger at the necking place after tensile deformation failure, so that the necking phenomenon is not obvious, which is due to the relatively small difference between the maximum uniform strain and the maximum strain; Numerical simulation of the effects of the threaded-rib structure and the light-circle structure on the deformation of the steel bars is carried out by the LS-DYNA algorithm: the analysis results show that the threaded-rib structure makes the steel bars better deformed during the tensile process, which is the result of the numerical simulation. The results show that the threaded rib structure makes the steel better deformed uniformly and absorbs the deformation energy in the tensile process. In summary, the macroscopic analysis of the deformation characteristics of the novel NPR bolt ductile material helps to better reveal its static tensile properties, which provides a valuable reference for quasi-static engineering practice.

     

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