Abstract The flat-jointed (FJ) contact model implemented in the particle flow code resolves the long-standing issue of the code producing unrealistically low ratios of uniaxial compressive strength (UCS) to direct tensile strength. Despite the improvements introduced with the FJ model, an FJ sample calibrated to the UCS still produces a crack initiation stress much lower than the expected value of approximately 0.4 UCS, as commonly observed in laboratory compression tests for most rocks. In this study, we investigated the role of initial crack volume on the crack initiation stress of a rock. We found that the microcracks among the mineral grains and their associated void space played a major role in controlling the stress magnitude associated with crack initiation. We also observed that the closure of these cracks between mineral grains was the primary driver of the crack closure phase in the compression test, and the elastic bimodularity was due to the crack density. We developed a methodology to incorporate the initial microcracks using the FJ contact model to match the crack closure stress and bimodularity of a laboratory rock sample. By introducing microcracks and voids among the mineral grains, we automatically capture the crack initiation stress of Lac du Bonnet granite measured at approximately 40% of the UCS.

中文翻译：

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初始裂纹体积对粘结粒子模型完整行为的影响

摘要 在粒子流代码中实现的平接 (FJ) 接触模型解决了代码产生不切实际的低单轴抗压强度 (UCS) 与直接拉伸强度比的长期问题。尽管 FJ 模型引入了改进，但校准到 UCS 的 FJ 样本仍会产生远低于预期值约 0.4 UCS 的裂纹起始应力，这在大多数岩石的实验室压缩测试中通常观察到。在这项研究中，我们研究了初始裂纹体积对岩石裂纹萌生应力的作用。我们发现矿物颗粒之间的微裂纹及其相关的空隙空间在控制与裂纹萌生相关的应力大小方面起着重要作用。我们还观察到，矿物颗粒之间这些裂缝的闭合是压缩试验中裂缝闭合阶段的主要驱动因素，而弹性双模性是由于裂缝密度造成的。我们开发了一种方法来使用 FJ 接触模型合并初始微裂纹，以匹配实验室岩石样品的裂纹闭合应力和双模性。通过在矿物颗粒中引入微裂纹和空隙，我们自动捕获了在大约 40% 的 UCS 处测量的 Lac du Bonnet 花岗岩的裂纹起始应力。