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立方体劈裂试验的应力公式借鉴于传统圆盘巴西试验,忽略了其三维效应,有效性难以保证。为了保证试验的有效性,得到更准确的应力公式,通过三维数值计算方法模拟立方体劈裂试验,结合Griffith强度理论分析其三维效应。分析得出,垫条比(垫条宽度和立方体边长的比值)和泊松比对立方体内应力分布影响较大。当垫条比取值一定时,泊松比取值越大,立方体内应力分布受应力集中影响越大,越难保证中心点起裂,而中心点起裂是立方体劈裂试验有效的前提,从而导致试验所测抗拉强度偏小;当泊松比取值一定时,垫条比取值越小,立方体内应力分布受应力集中影响越大,越容易在加载点附近出现应力凸起点,从而无法保证试验的有效性。为了保证试验的有效性,结合数值试验分析结果,对于不同的泊松比,推荐相应的垫条比取值范围,并在推荐范围内,建立考虑垫条比和泊松比的立方体劈裂强度修正公式。
The stress formula of cubic cleavage test is based on the traditional Brazilian test of Brazilian disc, ignoring its three-dimensional effect and its validity is difficult to guarantee. In order to ensure the validity of the experiment, a more accurate stress formula is obtained. The cubic cleavage test is simulated by three-dimensional numerical calculation method, and the three-dimensional effect is analyzed according to the Griffith intensity theory. The analysis shows that the ratio of the mat width (the ratio of the width of the mat to the length of the cube) and the Poisson’s ratio have a greater influence on the stress distribution in the cube. When the ratio of the strips is constant, the bigger the value of Poisson’s ratio is, the more the stress distribution in the cube is affected by the stress concentration, the more difficult it is to guarantee the initiation of the central point. The initiation of the central point is an effective prerequisite for the cube splitting test, Resulting in a small test tensile strength; when the Poisson’s ratio for a certain value, the smaller the value of the mat section, the stress distribution within the cube is more affected by the stress concentration, the more prone to stress in the loading point convex point, Thus can not guarantee the validity of the test. In order to ensure the validity of the experiment, combined with the results of numerical experiments, we recommend the corresponding range of cushion ratio for different Poisson’s ratio and establish the cube splitting strength correction considering the ratio of cushion and Poisson in the recommended range formula.