基于离散元的C-S-H凝胶微观徐变加速模拟方法

ACCELERATED DISCRETE ELEMENT MODELING METHOD FOR MICROSCALE CREEP OF C-S-H GEL

  • 摘要: 该文针对水化硅酸钙(C-S-H)凝胶的纳米压痕徐变性能,建立了一种离散元加速模拟方法。将速率过程理论(RPT, Rate Process Theory)引入C-S-H凝胶颗粒的接触本构,以描述切向粘性滑移速率与接触处切向/法向力的关系,并提出时间缩放算法,实现在离散元极小临界时间步长条件下对纳米压痕徐变试验仿真的加速计算。基于PFC(Particle Flow Code)构建不同堆积密度(0.74、0.64、0.58)的C-S-H凝胶颗粒集合体,通过墙体应力伺服施加等效内聚力,开展使用Berkovich压头的纳米压痕徐变试验仿真并完成参数标定。结果表明:该方法可再现压痕模量、硬度、接触徐变模量随堆积密度变化的标度关系;模拟结果揭示了压痕区颗粒运动和局部应力集中现象,从颗粒力学角度为纳米压痕徐变试验方法用于表征C-S-H凝胶长期徐变性能提供了合理性解释。该研究可为其它多孔颗粒/凝胶类材料的徐变性能加速模拟提供可借鉴的离散元建模框架。

     

    Abstract: This study develops an accelerated discrete element method (DEM) for simulating the nanoindentation creep behavior of calcium-silicate-hydrate (C-S-H) gel. Rate process theory (RPT) is incorporated into the contact constitutive law of C-S-H particles to relate the rate of tangential viscous slip to the tangential/normal contact forces. In addition, a time-scaling algorithm is proposed to accelerate the DEM simulation of nanoindentation creep under an extremely small critical time step. Using PFC3D, C-S-H particle assemblies with different packing densities (0.74, 0.64, and 0.58) are generated. An equivalent cohesive confinement is applied via wall-stress servo control, and nanoindentation creep simulations with a Berkovich indenter are performed for parameter calibration. The results show that the proposed method reproduces the scaling relationships of indentation modulus, hardness, and contact creep modulus with packing density. The simulations further reveal the evolution of particle motion and local stress concentration in the indentation zone, providing a particle-mechanics-based explanation for the rationality of using nanoindentation creep tests to characterize the long-term creep of C-S-H. This work offers a transferable DEM modeling framework for creep simulation of other porous granular/gel-like materials.

     

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