基于间接拉伸模式的沥青混合料内部力链分布特征

为了表征沥青混合料在间接拉伸模式下的力链分布特征，成型3种骨架结构沥青混合料的马歇尔试件，以及旋转压实试件和相应3种类型的沥青砂浆静压试件。利用简单性能试验分别测试不同温度条件下沥青混合料和沥青砂浆的动态模量、相位角，在获取沥青混合料旋转压实试件和马歇尔试件截面图像的基础上，结合数字图像处理技术和MATLAB编程，借助离散元方法重构了3种类型沥青混合料的旋转压实和马歇尔数字试件。对旋转压实数字试件进行虚拟简单性能试验，运用反演算法计算数字试件的细观参数，校验细观模型的准确性和合理性。对马歇尔数字试件开展虚拟间接拉伸试验，提取颗粒间接触力力链信息，以力链概率分布和角度分布作为量化指标进行分布特征分析。研究结果表明：利用离散元方法重构的3种骨架结构沥青混合料黏弹性细观模型具有较高的预测精度，动态模量和相位角的实测与预测最大差异分别为9.64%、0.24°；间接拉伸荷载模式下，3种骨架结构沥青混合料的内部法向压力力链概率分布均随f(接触力与平均接触力的比值)的增大而衰减，强力链(f≥1)的概率分布较小，而弱力链(f＜1)的概率分布较大，随着温度的升高，力链的最大概率分布基本呈增大的趋势；不同温度的压力力链角度分布差异较大，呈沿0°-180°水平线和90°-270°垂直线的非对称分布，0°-180°水平线以上分布占主导，随着温度的升高，角度分布均向外延伸，但延伸幅度不大，最大仅为3.954%；不同截面的沥青混合料具有一致的法向力链概率分布和角度分布。研究结果为从细观角度认知沥青混合料的非均匀力学响应及荷载传递演化提供了理论依据。

Distribution Characteristics of Force Chains in Asphalt Mixtures Based on Indirect Tensile Pattern

To characterize the distribution characteristics of force chains in asphalt mixtures subjected to indirect tensile loading pattern, Marshall specimens and gyratory compacted specimens of asphalt mixtures with three types of skeleton structures and the corresponding asphalt mastics specimens by static pressure method were prepared. Dynamic moduli and phase angles of asphalt mixtures and asphalt mastics were measured by the simple performance tests at different temperatures. On the basis of obtaining the section images of asphalt mixture specimens, the three digital specimens of Marshall and gyratory compacted asphalt mixtures with three skeleton structures were reconstructed using the discrete element method, combining the digital image processing technology and MATLAB programming. The meso-parameters of digital specimens were calculated using the inversion algorithm through the virtual simple performance test on the gyratory compacted digital specimens. Then the accuracy and rationality of the meso-models were verified. Additionally, virtual indirect tensile tests were carried out on Marshall digital specimens. The force chain information of contact force among particles was extracted, and the probability distribution and angle distribution of force chains were used as quantitative indexes to analyze the distribution characteristics. The research results show that the viscoelastic mesoscopic models of asphalt mixtures with three skeleton structures reconstructed by the discrete element method have high prediction accuracy. The maximum differences between the measured and predicted dynamic modulus and phase angle are 9.64% and 0.24°, respectively. Under the indirect tensile loading pattern, the probability distribution of normal compressive force chains attenuates with the increase of f (the ratio of the contact force to the average contact force). The strong force chain (f≥1) has a smaller probability distribution, while the weak force chain (f<1) has a larger probability distribution. The maximum probability distribution of force chains basically increases with the increase of temperature. Moreover, the angle distribution of compressive force chains is quite different at different temperatures, and has asymmetrical distribution along the 0°-180° horizontal line and 90°-270° vertical line. The angle distribution above the 0°-180° horizontal line dominates, and extends outward as the temperature increases, but the extent of extension with the maximum value of only 3.954% is not large. Different cross-sections from asphalt mixtures have consistent probability distribution and angle distribution of normal force chains. The research results provide a theoretical basis for understanding the heterogeneous mechanical responses and loading transmission evolution of asphalt mixture from a mesoscopic perspective.