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巴西圓盤劈裂二維及三維數值模擬研究

Numerical study of the Brazilian tensile test: 2D and 3D simulations

  • 摘要: 為揭示巴西圓盤起裂模式的變化規律及其破裂演化過程,運用連續介質彈塑性分析開展巴西圓盤劈裂二維及三維數值模擬研究。通過開展二維模擬研究,探究壓拉比及加載角對試樣起裂破壞模式的影響;通過三維模擬研究,探究圓盤試樣三維破裂面的形成及擴展過程。二維數值模擬結果表明,接觸加載角及壓拉比越大,巴西圓盤試樣越容易發生中心起裂;端部起裂由剪切破壞引起,而劈裂裂紋進一步擴展則由張拉破壞驅動。三維數值模擬結果表明,初始起裂點位于三維圓盤端面,隨加載角增大其逐漸向端面圓心移動;當圓盤發生端面中心起裂時,三維破裂面以弧形邊界向試樣內部發散擴展。無論圓盤試樣發生中心起裂還是端部起裂,由于三維效應巴西劈裂試驗可能都會低估巖石的抗拉強度。

     

    Abstract: The Brazilian splitting test is widely used to determine the tensile strength of rocks and rock-like materials due to its easy sample preparation and an easier compressive test setup as an indirect testing method compared with performing a direct uniaxial tensile test. However, the accuracy of this method has also been criticized for a long time in the literature since its introduction. This paper carried out two-dimensional (2D)/three-dimensional (3D) numerical simulations of the Brazilian tensile test using a continuum elastoplastic analysis to reveal the variation of fracture modes of the Brazilian disk and its fracture evolution process. The effect of compression-tension ratios and contact loading angles on the fracture modes of the disk specimens was studied through 2D simulations. Through 3D simulations, the initiation and expansion processes of the 3D fracture under different loading angles were explored. The simulated results of failure modes, stress distributions, and calculated tensile strengths were analyzed. The 2D numerical results show that the larger the contact loading angle and the compression–tension ratio, the more likely the Brazilian disk specimens crack first at the disk center. The fracture initiation under the loading rims is caused by shear failure, but further propagation of the split fracture is driven by tension failure. The 3D numerical simulation results show that the crack initiation point is always located on the end face of the disk and gradually moves to the center from the loading ends as the loading angle increases. When the central tensile cracking appears, the 3D fracture expanded toward the inside of the specimen with an arc boundary. Regardless of whether the disk specimen starts to fracture initially at the disk center or the loading points, the Brazilian tensile test may underestimate the tensile strength of rocks due to the 3D effect.

     

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