Mineral grain size heterogeneity is one of the fundamental reasons leading to differences in rock mechanical behaviours. Several indices have been proposed to quantify grain size heterogeneity, however, the applicability of the existing indices is limited due to various preconditions. An improved grain size heterogeneity index H_e was proposed in this study. By comparing with the previous index, the improved index was proved to be more applicable for analysing rock mechanical properties. Through a series of grain-based model (GBM), the grain size heterogeneity effect, material heterogeneity effect and mineral content effect were further discussed. For a simple grain size heterogeneity effect, the crack initiation stress, damage stress, peak stress and crack initiation stress ratio of rock decreased linearly as the improved index H_e increased. After accounting for the material heterogeneity effect, the above characteristic stresses and elastic modulus decreased. A significant material heterogeneity effect and mineral content effect will impact the linear correlation between the rock macro-mechanical parameters and the H_e index. When the axial stress was low, the grain size heterogeneity had little effect on the number of microcracks, but this heterogeneity became the main factor affecting the evolution of microcracks as the axial stress increased. The number of intragrain tensile cracks increases and the number of intergrain shear cracks decreases with increasing H_e, when the axial stress reached the rock peak strength. Besides, the combined effects of material heterogeneity and mineral content may control the type and number of microcracks, further weakening the effect of grain size heterogeneity.

矿物粒度的非均质性是导致岩石力学行为差异的根本原因之一。已经提出了几个指标来量化晶粒尺寸异质性，但是，由于各种先决条件，现有指标的适用性受到限制。一种改进的晶粒尺寸不均匀性指数ħ _ë本研究中提出。通过与以往指标的对比，证明改进后的指标更适用于岩石力学性质的分析。通过一系列基于晶粒的模型（GBM），进一步讨论了晶粒尺寸异质性效应、材料异质性效应和矿物含量效应。对于一个简单的晶粒尺寸不均匀性的效果，岩石的裂纹萌生的应力，破坏应力，峰值应力和裂纹萌生的应力比为改进的索引线性下降ħ _ë增加。考虑到材料异质性影响后，上述特征应力和弹性模量下降。显着的材料非均质效应和矿物含量效应将影响岩石宏观力学参数与^ h _É指数。当轴向应力较低时，晶粒尺寸不均匀性对微裂纹数量的影响不大，但随着轴向应力的增加，这种不均匀性成为影响微裂纹演化的主要因素。的晶内拉伸裂纹增加，并且数量的粒间剪切裂缝的数目随增加而减小ħ _é，当轴向应力达到岩高强度。此外，材料非均质性和矿物含量的共同作用可以控制微裂纹的类型和数量，进一步削弱晶粒尺寸非均质性的影响。