The present work studies the Park–Paulino–Roesler (PPR) model, a unified potential-based cohesive zone model (CZM), for mixed mode I/II fractures in different rank coals, including weakly caking coals, fat coals and anthracite, by using disk-shaped compact tension (DC(T)) tests and punch-through shear (PTS) tests. The PTS experiments show that with the increase in coal rank, the initial shear stiffness and shear peak loads grow and the maximum tangential crack opening displacement (δ_t) decreases gradually. Additionally, the post-peak softening curve tends to have a linear shape, and the shear crack surface is rougher and more tortuous for the lower rank coals. The mode II fracture energy (Φ_t) was evaluated by calculating the area under the shear load–displacement curves. Φ_t is remarkably higher than mode I fracture energy (Φ_n) for the same coal rank, and the average value of Φ_t decreases from 145.54 J/m² to 70.11 J/m² as the coal rank of the specimens increases from weakly caking coals to anthracite. In order to verify the obtained PPR CZMs, mixed mode I/II single-edge notched beam (SENB) tests were performed and the experimental results are in good agreement with the numerical simulation. Moreover, we conducted SENB tests with different-size specimens, and the established PPR CZM model demonstrated its ability of describing the size effect of the mixed mode I/II fracture in coals.

目前的工作研究了Park-Paulino-Roesler（PPR）模型，这是一个基于势能的统一的粘聚带模型（CZM），用于通过不同等级的煤（包括弱结块煤，肥煤和无烟煤）的I / II混合模式裂缝。使用圆盘形紧凑拉伸（DC（T））测试和穿通剪切（PTS）测试。该PTS实验表明，与在煤级的增加，初始剪切刚度和剪切峰值负荷增长和最大切向裂纹开口位移（δ_吨）逐渐减小。另外，峰后软化曲线趋向于具有线性形状，并且对于较低等级的煤，剪切裂纹表面更粗糙且更曲折。模式II破坏能量（Φ_吨通过计算剪切载荷-位移曲线下的面积来评估）。Φ_吨是显着高于模式I断裂能量（Φ _Ñ对于相同的煤级），和的平均值Φ_吨从145.54焦耳/米减小²至70.11焦耳/米²随着样品的煤级从弱粘结煤增加到无烟煤。为了验证所获得的PPR CZM，进行了混合模式I / II单边切口光束（SENB）测试，实验结果与数值模拟吻合良好。此外，我们对不同尺寸的样本进行了SENB测试，并且已建立的PPR CZM模型证明了它能够描述煤中I / II型混合模式裂缝的尺寸效应。