沥青混合料蠕变损伤模型与损伤演化

为定量描述沥青混合料的蠕变特性，考虑沥青混合料在整个蠕变过程中同时存在蠕变硬化机制和蠕变损伤劣化机制，基于分数阶微积分理论，发展了一种相对简单的分数阶蠕变损伤模型，用分数阶Maxwell模型来描述蠕变硬化机制，用损伤应变来表示蠕变损伤劣化机制，并从统计学角度推导出沥青混合料的损伤演化方程；对AC-13沥青混合料进行了不同应力水平(0.179、0.358、0.448、0.537和0.716 MPa)下的单轴压缩蠕变试验，通过Levenberg-Marquardt优化算法进行了非线性拟合，确定了不同应力水平下分数阶蠕变损伤模型的参数与损伤演化曲线；为构建不同应力水平下统一的损伤演化模型，提出了一种统计量化沥青混合料损伤演化的方法，建立了蠕变损伤与损伤应变之间的演化关系。研究结果表明:在不同应力水平下，提出的分数阶蠕变损伤模型与试验结果的判定系数均不小于0.995，适用于描述包括衰减蠕变阶段、稳定蠕变阶段和加速蠕变阶段的整个蠕变过程；在衰减蠕变阶段，不同应力水平下沥青混合料的损伤都小于1.0×10-3，相对于蠕变破坏时的损伤0.8可以忽略不计，而进入稳定蠕变阶段以后，损伤逐渐增大；当沥青混合料的蠕变应力超过一定值时会发生蠕变破坏，其流值时间取决于所施加的应力水平；用二参数Weibull分布函数拟合所得的蠕变损伤与损伤应变之间演化关系的判定系数为0.992，说明可以建立不同应力水平下的统一损伤演化模型，且其参数只与材料性能和温度有关，与施加应力大小无关。 

Creep damage model and damage evolution of asphalt mixtures

To quantitatively evaluate the creep characteristics of asphalt mixtures, the mechanisms associated with both creep hardening and creep damage and deterioration throughout the creep process of asphalt mixtures were considered. Based on the fractional calculus theory, a relatively simple fractional creep damage model was developed. In this model, a fractional Maxwell model was used to describe the creep hardening mechanism, and the damage strain was used to represent the creep damage and deterioration mechanism. In addition, a damage evolution equation for asphalt mixtures was statistically derived. Uniaxial compressive creep tests were performed on AC-13 asphalt mixtures at different stress levels (0.179, 0.358, 0.448, 0.537, and 0.716 MPa). The nonlinear fitting was carried out using the Levenberg-Marquardt optimization algorithm to determine the parameters of fractional creep damage model as well as the damage evolution curves at different stress levels. To construct a unified damage evolution model for different stress levels, a method to statistically quantify the damage evolution of asphalt mixtures was proposed, and the evolution relationship between the creep damage and the damage strain was established. Research results show that the determination coefficients between the proposed fractional creep damage model results and the test results at different stress levels are all not less than 0.995, indicating that the proposed model is suitable for describing the entire creep process including the decay, stable, and accelerated creep stages. In the decay creep stage, the damage of asphalt mixture at different stress levels is less than 1.0×10-3 and is negligible compared to the damage (0.8) at creep failure. In the stable creep stage, the damage gradually increases. Eventually, the asphalt mixture undergoes creep failure when the creep stress exceeds a certain value. The flow time depends on the applied stress level. The determination coefficient of evolution relationship between the creep damage and the damage strain fitted by the two-parameter Weibull distribution function is 0.992. This indicates that one damage evolution model can be developed for different stress levels. Its parameters are only related to material properties and temperature and are independent of the applied stress. 2 tabs, 10 figs, 32 refs.