To highlight the advantages of autonomous vehicles (AVs) in modern traffic, it is necessary to investigate the sensing requirement parameters of the road environment during the vehicle braking process. Based on the texture information obtained using a field measurement, the braking model of an AV was built in Simulink and the ride comfort under typical braking scenarios was analyzed using CarSim/Simulink co-simulation. The results showed that the proposed brake system for the AV displayed a better performance than the traditional ABS when considering pavement adhesion characteristics. The braking pressure should be controlled to within the range of 4 MPa similar to 6 MPa on a dry road, while in wet road conditions, the pressure should be within 3 MPa similar to 4 MPa. When steering braking in dry road conditions, the duration of the "curve balance state" increased by about 57.14% compared with wet road conditions and the recommended curve radius was about 100 m. The slope gradient had a significant effect on the initial braking speed and comfort level. Overall, the ride comfort evaluation method was proposed to provide theoretical guidance for AV braking strategies, which can help to complement existing practices for road condition assessment.

为改善路面结构抗反射裂缝能力,提升沥青路面材料循环利用率,将复合改性橡胶沥青与路面循环利用技术综合运用于应力吸收层中,设计制备了复合改性橡胶沥青再生混合料AC-10。通过沥青胶结料试验研究比较了复合改性橡胶沥青、SBS改性沥青、

A new method, the notched specimen cracking test (NSCT), is presented to directly measure the thermal stress and critical temperature of asphalt binders at low temperatures. The NSCT contains a notched specimen that contraction deformation is limited by special invar steel fixtures exposed to a continuous cooling temperature field provided by a programable environmental chamber. To simulate the actual thermal contraction state-strain level of asphalt pavement in the laboratory, the geometry of the binder specimen was carefully designed by theoretical computation based on the superposition principle. The preliminary test result shows that NSCT for evaluation of the potential cracking risk of modified or non-modified binders at low temperatures is reliable and easy to operate. The coefficient of variations of thermal stress results is at least 50% smaller than the traditional thermal cracking measurement method.

轮胎与路面间的附着特性是影响车辆行驶安全性的最重要因素之一.雨天条件下沥青路面容易产生水膜,由于流体动力润滑作用使得轮胎相对于粗糙路面发生了一定距离的滑移,产生滑水现象,在很大程度上影响胎路之间的附着特性.根据雨天情况下

As the main objective influencing factor on the brake safety of autonomous vehicles, pavement texture information is directly related to road surface antiskid performance. However, in the brake system of autonomous vehicles, the influence of road surface adhesion characteristics on braking stability is seldomly considered. To study the braking stability of autonomous vehicles on curved sections under different road conditions, the advanced close-range photogrammetry system was utilized to extract the road surface texture information. Thereafter, the power spectral density (PSD) of the road surface was calculated by MATLAB to obtain the pavement adhesion coefficient curves based on the Persson friction theory model under different road conditions. Considering the pavement adhesion characteristics, the braking model of autonomous vehicles was built in Simulink, and then, the braking performance on curved sections was analyzed with CarSim/Simulink cosimulation. The results indicate that, according to the adhesion coefficient of different asphalt pavement types under different road conditions, the ranking order is open-grade friction course (OGFC) > stone matrix asphalt (SMA) > dense-graded asphalt concrete (AC). In addition, both the maximum lateral offset distances and the maximum lateral forces of the tires decrease as the curve radius gradually increases under different road conditions. It can also be found that there is a relatively uniform vertical forces distribution of the tire when the curve radius is no less than 100 m, and the limit speed of the vehicle varies parabolically with increasing in curve radius. Compared with dry road, the reduction of vehicle braking deceleration is more significant and the yaw rate is greater on wet road. Last but not least, the braking comfort with a radius of 200 m is the best according to the comfort index (CI) in International Standard ISO, in which the comfort level can be sorted into six levels.

为合理表征沥青混合料的细观特性，并深入研究沥青混合料低温开裂过程中温度应力积累和裂缝扩展的细观机理，基于离散元程序PFC2D建立沥青混合料约束试件温度应力（TSRST）模拟试验方法。根据逆向体视学原理和概率论方法，引入沥青混合料三维体积级配与二维数量级配的转化关系，建立二维离散元虚拟试件；结合沥青混合料各组分之间的接触行为特点，赋予不同的接触本构模型，借助室内试验测定集料和沥青砂浆的宏观参数，推导得到不同温度下各相材料间的细观接触参数；通过TSRST模拟试验，分析试件内部温度场变化规律、温度应力曲线、细观接触力的分布特征以及低温开裂的细观机理。研究结果表明：TSRST离散元模拟和室内试验的结果具有较高的吻合度，断裂温度相对误差为3.7%,断裂强度相对误差为4.8%,TSRST模拟试验具有较高的准确性，能够作为试件低温抗裂性评价的可靠方法；试件的破坏可以分为3个阶段：（1）起裂阶段，在转化点温度前，试件内部个别接触点接触失效，对结构整体受力状况影响较小；（2）稳定扩展阶段，温度达到断裂温度前，随着温度的降低，接触力增加，裂缝沿试件薄弱部位发展，微裂缝数量缓慢稳定增长；（3）不稳定扩展阶段，温度达到断裂温度后，短时间内温度应力下降了66%,裂缝总量增加了132条，微裂缝已汇聚成可见的宏观裂缝，并沿着构造相对薄弱的位置快速扩展，导致试件失去整体承载力。

To clarify the intrinsic relationship between the mechanical properties of asphalt and its fraction composition, the SARA fraction composition and six macroscopic mechanical properties (critical cracking temperature (TCR), fatigue life (Nf), non-recoverable creep (Jnr3.2), penetration, ductility, and softening point) were investigated for 16 asphalt samples. Fraction contents of asphaltene and aromatic are strongly correlated with TCR and ductility (R2 > 0.92) that characterize the ability of asphalt to adapt to deformation at low and medium temperatures. Heavy fraction (asphaltene and resins) content is also strongly correlated with (R2 > 0.90) penetration and Jnr3.2 that characterize the resistance of the asphalt to overall deformation at medium and high temperatures. To express the changes in the four fractions simultaneously with one indicator, a statistic, average deviation of the fractions between the given asphalt and its original (marked sigma), is introduced in this study to characterize the degree of asphalt aging based on the fraction changes. It normalizes the four simultaneous change indicators (percentage of SARA fractions) during asphalt aging into one indicator. This new indicator has a strong correlation with several mechanical performance indicators of asphalt, where it is strongly correlated with TCR (R2 > 0.90), ductility, and penetration, which are also well correlated with Jnr3.2 (R2 > 0.85), Nf (R2 > 0.75), and softening point (R2 > 0.75).

To investigate the flow characteristics of pore water in asphalt pavement and the variation law of the pore water pressure under vehicle loading, a novel method based on BA network and quartet structure generation set method was proposed to reconstruct the three-dimensional (3D) pavement model with pores. The permeability coefficient and the gradation curve were adopted to evaluate the reliability and stability of the random growth pavement model. Then, the tire-fluid-pavement coupling model was established with FLUENT 3D based on the fluid Mie-Gruneisen state equation. According to the built fluid-solid coupling model, the pressure-velocity coupled finite volume algorithm was applied to study the distribution of the pore water pressure in asphalt pavement. Results show that the pore water pressure in asphalt pavement decays periodically with time under vehicle loading. For different types of asphalt pavement, the pore water pressure in open-graded friction course (OGFC) pavement is the smallest during the whole process. Moreover, the peak values of the pore water pressure decrease in the order of asphalt concrete (AC) pavement, stone mastic asphalt (SMA) pavement, and OGFC pavement. The maximum negative value of the pore water pressure is generally less than 0.3 times the maximum positive values. As for saturated pavement pores, the pore water pressure is hardly affected by the water film thickness. The positive peak value of the pore water pressure increases on an approximate parabolic curve as the vehicle speed improves gradually, while the negative one remains largely unchanged. The results are expected to help reduce tire hydroplaning risk and provide guidance for the selection of asphalt mixtures of drainage asphalt pavement.