Deformation and Failure of Concrete Splitting Based on DIC Method
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摘要: 混凝土是一种典型的拉压不对称准脆性复合材料，采用巴西劈裂试验研究其拉伸破坏时发现，不同加载方式对混凝土的变形和破坏特征的影响很大。通过直接加载、弧形垫块加载以及平台圆盘加载3种方式对混凝土圆盘试件进行准静态试验，基于数字图像相关法，研究混凝土拉伸劈裂破坏过程中的全场变形和局域化破坏特征。结果表明：(1) 标准圆盘直接加载时，试件顶部和底部附近的应力集中使试件端部先发生损伤，拉伸应变场中的高幅值区从加载端向中心迅速扩展；而采用弧形垫块或平台圆盘加载优化了应力集中问题，使得试件中心最先出现应变集中，继续加载时损伤向两端扩展，导致试件劈裂破坏。(2) 弧形垫块加载和平台圆盘加载满足了巴西劈裂试验的中心起裂假设。测得平台圆盘加载时混凝土试件的抗拉强度约为5 MPa, 比标准圆盘加载提高了31.2%左右，分析认为平台圆盘加载提高了试件中心的压拉比以及加载端处的摩擦力。(3) 3种加载方式下，混凝土试件中心位置变形的数字图像相关分析结果和应变试验测量结果吻合较好，验证了基于数字图像相关方法获得的混凝土试件全场变形的有效性。Abstract: Concrete is a typical quasi-brittle composite material with tension-compression asymmetry. When the tensile failure is studied by Brazilian splitting test, different loading methods have great impact on the deformation and failure characteristics of concrete. The quasi-static splitting tests of standard disk direct loading, arc loading and flattened disk loading are carried out. Based on the digital image correlation method, the full-field deformation and localized failure characteristics in the process of concrete tensile splitting are studied. The results are as follows. (1) For the direct loading of the standard disk, the stress concentration near the top and bottom of the specimen makes the damage concentration occur preferentially at the end of the specimen, and the high amplitude area in the tensile strain field expands rapidly from the loading end to the center; due to the improvement of stress concentration by the arc loading and flattened disk loading, the strain concentration firstly appears near the center of the specimen and continues to expand from the center to both ends until the crack penetrates the specimen. (2) Arc loading and flattened disk loading meet the central initiation hypothesis of Brazilian splitting experiment; the tensile strength of concrete specimen measured by the flattened disk is about 5 MPa, which is about 31.2% higher than the standard disk due to the greater friction at the loading position and greater central compression tension ratio. (3) Under the three loading methods, the DIC analysis results of the deformation at the center of the specimen are in good agreement with the measurement results of the strain gauge, which verifies the effectiveness of the full-field deformation of the concrete specimen obtained based on the DIC method.
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Key words:
- concrete /
- digital image correlation method /
- strain evolution /
- Brazilian splitting test
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图 2 混凝土试件正面散斑(a)和反面应变片(b)
Figure 2. Concrete specimen with speckle on the front (a) and strain gauge on the back (b)
图 5 弧形垫块加载下标准圆盘的载荷-时间曲线
Figure 5. Load-time curves of standard disks between loading arcs
图 6 弧形垫块加载下标准圆盘的拉伸应变场演化
Figure 6. Evolution of tensile strain field of standard disks between loading arcs
图 9 准静态劈裂试验得到的试样载荷-时间曲线
Figure 9. Load-time curves of specimen inquasi-static splitting test
图 10 DIC结果与应变计测量结果的对比
Figure 10. Comparison between tensile strain determined from DIC analysis and that measured by strain gauges
表 1 混凝土试件的配合比
Table 1. Mix proportion of concrete specimen
Material Proportion/(kg·m–3) Cement 398.93 Water 195.00 Fine aggregate 632.12 Coarse aggregate 1173.95 
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表 2 3种圆盘加载试验得到的抗拉强度
Table 2. Tensile strength of three disc loading test
No. Loading methods pc/kN Tensile strength/MPa Average tensile strength/MPa BD-01 Standard disk
direct loading31.868 4.058 3.836 BD-02 31.374 3.995 BD-03 29.806 3.795 BD-04 29.622 3.772 BD-05 29.382 3.741 BD-06 28.688 3.653 ArcBD-01 Standard disk
arc loading31.342 3.851 4.007 ArcBD-02 35.233 4.328 ArcBD-03 30.647 3.765 ArcBD-04 33.788 4.151 ArcBD-05 32.277 3.965 ArcBD-06 32.416 3.982 FBD-01 Flattened disk loading 40.400 4.914 5.031 FBD-02 38.235 4.651 FBD-03 39.753 4.836 FBD-04 44.417 5.403 FBD-05 43.854 5.334 FBD-06 41.511 5.050
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