沥青砂粘弹特性实验研究

进行了沥青砂在不同加载应力和不同实验温度下单轴压缩蠕变实验,得到其在不同实验条件下的蠕变曲线,选择Burgers模型,编制非线性拟合程序,求得模型参数值,通过相关性分析,得到了模型参数与温度和应力函数关系式,分析了模型参数对沥青砂蠕变性能的影响,最后进行模型预测值与实验结果对比,结果表明Burgers模型能够描述沥青砂蠕变过程的第一阶段、第二阶段,反映了其粘弹特性。     

基于Eshelby等效夹杂理论的沥青混合料有效粘弹性质分析

利用Eshelby 等效夹杂理论研究了沥青混合料的单轴压缩蠕变行为。通过时间域内的Laplace 变换将问题线性化, 得到了沥青混合料的蠕变本构关系。开展了不同温度、应力水平条件下沥青砂的单轴压缩蠕变实验, 根据数据拟合了沥青砂四参量流变模型的模型参数。在此基础上, 预测了沥青混合料在不同温度、应力水平下的蠕变曲线, 分析了温度、应力水平对沥青混合料蠕变行为的影响。结果表明:在相同的应力水平下, 沥青混合料的应变和应变率都随温度的升高而增大, 并且在沥青软化点附近发生明显突变;在相同的温度下, 沥青混合料的应变和应变率都随加载应力的增加而增大。     

沥青混合料非线性黏弹塑性蠕变模型

本研究采用非线性黏弹塑性蠕变模型,更好地来模拟沥青混合料蠕变全过程。该模型由Burgers模型和非线性黏塑性元件串联而成。通过对沥青混合料的单轴压缩蠕变实验,得到不同应力作用下应变随时间的变化规律以及不同温度条件下沥青混合料蠕变柔量随时间的变化规律。利用origin软件对实验数据进行拟合,得到非线性黏弹塑性蠕变模型的六个力学参数。模型模拟结果与实验结果一致,表明本文所建立的非线性黏弹塑性蠕变模型的正确与合理性。此模型可较好地描述沥青混合料加速蠕变阶段,弥补了Burgers模型的不足。     

沥青砂混合料粘弹塑力学特性研究

在0.1MPa、0.15MPa、0.2MPa、0.25MPa和0.3MPa下进行了沥青砂试样单轴压缩和蠕变实验,分析了其压缩和蠕变性质,根据变形机理提出了粘弹塑本构模型可由粘弹性和粘塑性的两个子模型串联构成,通过对粘塑性子模型中粘性系数进行改进,理论推导了模型蠕变本构方程,确定了模型参数,并求得模型参数与加载应力函数关系。进行模型预测与实验结果对比,结果表明:该模型能够描述沥青砂试样在不同应力下蠕变变形的3个阶段,反映了沥青砂混合料粘弹塑变形特点。     

考虑时效损伤劣化的变参数非线性蠕变损伤模型

应力长期作用下岩体内部损伤不断累积、扩展,导致部分承载单元丧失承载能力,使得岩体内部真实应力强度大于表观应力。该文以流变学理论为基础,将损伤因子引入弹性元件及黏性元件中,给出弹性损伤元件及黏性损伤元件的蠕变特征方程,用以描述持荷过程中由于损伤累积而呈现出蠕变与时间相关的非线性变形特征;然后以弹性损伤元件及黏性损伤元件的蠕变特征方程为基础,给出考虑损伤效应的经典组合模型的蠕变状态方程,并依据稳定蠕变过程中蠕变变形的组成特征,构建了用于描述软岩稳定蠕变的五元件变参数非线性蠕变损伤模型,同时给出了蠕变损伤组合模型的蠕变变形特征方程;最后以江西东乡铜矿砂质页岩稳定蠕变阶段实验数据为基础,分析并验证了蠕变损伤模型在描述软岩非线性蠕变特征方面的准确性及适用性,拟合结果表明:引入损伤因子的蠕变模型元件,能够很好的描述蠕变的时效-非线性特征。     

基于蠕变试验的沥青粘弹性损伤特性

通过BBR-弯曲梁流变仪在不同温度下进行沥青小梁蠕变试验,得到了不同温度下的蠕变柔量曲线。通过移位,按WLF公式推导得到了不同温度下的移位因子和各个温度下的蠕变柔量主曲线簇。用Weibull函数来描述沥青内部缺陷的分布,将Burgers粘弹性模型与连续损伤因子模型二者耦合建立了沥青的粘弹性损伤模型。理论模型和试验结果比较吻合,表明在沥青粘弹性性能评价过程中考虑损伤效应的影响是必要的。     

竹木复合层合板疲劳与循环蠕变的累积损伤研究

为了对疲劳与循环蠕变交互作用下的损伤进行定量描述,采用一种考虑应变比率和弹性模量2个参数共同描述损伤的变量,并建立了损伤力学模型,该模型能够综合表现疲劳循环过程中塑性应变变化和弹性模量变化规律。通过对竹木复合层合板在80%、75%和70%3种应力水平下的纯疲劳弯曲试验,得出其损伤变量变化规律的实验曲线。通过对力学模型进行分段求解的方法,得到了竹木复合层合板在疲劳与循环蠕变交互作用下的累积损伤的拟合曲线。结果表明,该损伤参量及损伤模型可以较准确的描述在疲劳与循环蠕变交互作用下竹木复合层合板的损伤累积变化规律。     

316L不锈钢的高温疲劳蠕变行为和寿命预测

进行316L不锈钢在单级和两级载荷作用下的高温疲劳蠕变试验,研究了载荷历程效应对材料行为的影响.在已有统一的疲劳蠕变损伤演化模型基础上,得到了316L高温单级载荷作用下非线性损伤演化曲线.同时,建立了一种耦合载荷历程效应的多级疲劳蠕变载荷作用下的材料破坏准则.基于该破坏准则,结合材料的非线性损伤模型对316L不锈钢高温两级载荷作用下的疲劳蠕变寿命进行了预测,预测结果与试验数据符合得比较好.     

基于全场等效损伤测试的累积损伤模型

在固定的一组循环数下，对其中每一预定循环数进行不同应力水平的疲劳试验，并测出材料的韧性变化率，以此为损伤变量得到该组循环数下损伤量与交变应力水平关系的曲线族。该曲线族可以转换成相同损伤量下交变应力与循环数关系的等效损伤线族，通过对三种材料等效损伤线族测试和分析，给出损伤线族方程表达式，由此得到的累积损伤模型可以计算复杂加载下材料的剩余寿命，多级加载实验结果与测试值较好符合。     

ECC单轴受拉损伤本构模型研究EI北大核心CSCD

通过单轴拉伸试验,讨论了PVA纤维体积掺入量和水胶比对工程用水泥基复合材料(ECC)受拉力学性能参数(开裂应变、开裂应力、峰值应变、峰值应力、极限应变以及应力-应变关系曲线)的影响规律。基于此,从损伤力学的角度讨论了ECC在单轴受拉过程的开裂前阶段、应变硬化阶段以及应变软化阶段的损伤演化机制。进而,基于ECC受拉损伤演化机制提出ECC受拉损伤本构模型,并给出模型相关参数的计算方法,分析表明:该文提出损伤模型得到的ECC受拉损伤演化曲线能更为合理的描述ECC的损伤演化全过程。最后,该文损伤模型计算的ECC受拉应力-应变关系曲线和试验曲线对比结果表明,所提出的模型能够合理的描述ECC受拉非线性应力-应变关系特征,且具有良好的精度。     

Mechanism and behavior of fiber-reinforced asphalt mastic at high temperature

Abstract

The rheological behaviour and reinforcement mechanism of asphalt mastic mixed with fibres at high temperature were investigated in this study. Fibres, including basalt, polyester and glass, were added to asphalt mastic. Repeated creep and multi-stress creep tests were conducted to characterise the high-temperature properties of the mastic, and numerical simulation was performed with ABAQUS software to analyse the reinforcement effect of fibres. Test results indicate that the fibres have excellent reinforced performance; for example, the accumulated strain and its change rate decrease, and its creep stiffness modulus increases after the fibres are mixed into the mastic. The creep recovery rate increases, and its creep residual value decreases at a high stress level. The creep stiffness modulus under different loading cycles can be expressed by a power function. Numerical simulation shows that the fibres effectively absorb mastic stress; hence, creep strain in the mastics decreases. The Burgers model was utilised to present the rheological behaviours of mastics with fibres; the model parameters were estimated.     

Development of a stress-mode sensitive viscoelastic constitutive relationship for asphalt concrete: experimental and numerical modeling

Asphalt binder is responsible for the thermo-viscoelastic mechanical behavior of asphalt concrete. Upon application of pure compressive stress to an asphalt concrete specimen, the stress is transferred by mechanisms such as aggregate interlock and the adhesion/cohesion properties of asphalt mastic. In the pure tensile stress mode, aggregate interlock plays a limited role in stress transfer, and the mastic phase plays the dominant role through its adhesive/cohesive and viscoelastic properties. Under actual combined loading patterns, any coordinate direction may experience different stress modes; therefore, the mechanical behavior is not the same in the different directions and the asphalt specimen behaves as an anisotropic material. The present study developed an anisotropic nonlinear viscoelastic constitutive relationship that is sensitive to the tension/compression stress mode by extending Schapery’s nonlinear viscoelastic model. The proposed constitutive relationship was implemented in Abaqus using a user material (UMAT) subroutine in an implicit scheme. Uniaxial compression and indirect tension (IDT) testing were used to characterize the viscoelastic properties of the bituminous materials and to calibrate and validate the proposed constitutive relationship. Compressive and tensile creep compliances were calculated using uniaxial compression, as well as IDT test results, for different creep-recovery loading patterns at intermediate temperature. The results showed that both tensile creep compliance and its rate were greater than those of compression. The calculated deflections based on these IDT test simulations were compared with experimental measurements and were deemed acceptable. This suggests that the proposed viscoelastic constitutive relationship correctly demonstrates the viscoelastic response and is more accurate for analysis of asphalt concrete in the laboratory or in situ.     

Micromechanical finite element framework for predicting viscoelastic properties of asphalt mixtures

A micromechanical finite element (FE) framework was developed to predict the viscoelastic properties (complex modulus and creep stiffness) of the asphalt mixtures. The two-dimensional (2D) microstructure of an asphalt mixture was obtained from the scanned image. In the mixture microstructure, irregular aggregates and sand mastic were divided into different subdomains. The FE mesh was generated within each aggregate and mastic subdomain. The aggregate and mastic elements share nodes on the aggregate boundaries for deformation connectivity. Then the viscoelastic mastic with specified properties was incorporated with elastic aggregates to predict the viscoelastic properties of asphalt mixtures. The viscoelastic sand mastic and elastic aggregate properties were inputted into micromechanical FE models. The FE simulation was conducted on a computational sample to predict complex (dynamic) modulus and creep stiffness. The complex modulus predictions have good correlations with laboratory uniaxial compression test under a range of loading frequencies. The creep stiffness prediction over a period of reduced time yields favorable comparison with specimen test data. These comparison results indicate that this micromechanical model is capable of predicting the viscoelastic mixture behavior based on ingredient properties.     

New achievements in visco-elastoplastic constitutive model and temperature sensitivity of glasphalt

This paper focuses on the experimental investigation on temperature sensitivity and visco-elastoplastic behaviour of glasphalt. Classic Burgers creep model could only describe the viscoelastic behaviour of materials before the third creep-phase, so a viscoplastic string is added in series with classic Burgers model in order to predict the visco-elastoplastic behaviour of glasphalt. In this research, the effects of loading stress and temperature on creep behaviour of glasphalt under dynamic loading are investigated. In addition, some methods were used to solve model parameters and then predictions from proposed model were compared with experimental results. It was shown that creep testing curves coincided well with theoretic curves, validating that modified Burgers model can completely characterise creep behaviour of glasphalt. Besides, temperature sensitivity of glasphalt was evaluated by using indirect tensile stiffness modulus test, and stiffness modulus behaviour model of glasphalt was presented based on the experimental results and numerical analysis.     

Dynamic modulus simulation of the asphalt concrete using the X-ray computed tomography images

The objective of this study is to predict the dynamic modulus of asphalt mixture using both two-dimensional (2D) and three-dimensional (3D) Distinct Element Method (DEM) generated from the X-ray computed tomography (X-ray CT) images. The 3D internal microstructure of the asphalt mixtures (i.e., spatial distribution of aggregate, sand mastic and air voids) was obtained using the X-ray CT. The X-ray CT images provided exact locations of aggregate, sand mastic and air voids to develop 2D and 3D models. An experimental program was developed with a uniaxial compression test to measure the dynamic modulus of sand mastic and asphalt mixtures at different temperatures and loading frequencies. In the DEM simulation, the mastic dynamic modulus and aggregate elastic modulus were used as input parameters to predict the asphalt mixture dynamic modulus. Three replicates of a 3D DEM and six replicates of a 2D DEM were used in the simulation. The strain response of the asphalt concrete under a compressive load was monitored, and the dynamic modulus was computed. The moduli of the 3D DEM and 2D DEM were then compared with both the experimental measurements results. It was revealed that the 3D discrete element models successfully predicted the asphalt mixture dynamic modulus over a range of temperatures and loading frequencies. It was found that 2D discrete element models under predicted the asphalt mixture dynamic modulus.     

Analytical modeling and experimental study of tensile strength of asphalt concrete composite at low temperatures

In this study, analytical modeling of the tensile strength of hot-mix asphalt (HMA) mixtures at low temperatures was developed. To do this, HMA mixtures were treated as a two-phase composite material with aggregates (coarse and fine) dispersed in an asphalt mastic matrix. A two-phase composite model, which was similar to Papanicolaou and Bakos's [J. Reinforced Plast. Compos. 11 (1992) 104] model with a particle embedded in an infinite matrix, was proposed. Unlike Papanicolaou and Bakos's model, an axial stress was introduced to the fiber end to consider the load transferred from the asphalt mastic the aggregate. Efforts were also made to consider the effect of aggregate gradation, asphalt mastic degradation, and interfacial damage between the aggregates and asphalt mastic matrix on the tensile strength of the HMA mixtures. Experimental investigations were conducted to validate the developed theoretical relations. A reasonable agreement was found between the predicted tensile strength and the experimental results at low temperatures. Parameters affecting the tensile strength of asphalt mixtures were discussed based on the calculated results.     

Shear creep response of an airport asphalt mastic

Two runways were resurfaced with 50–60 mm of typical airport asphalt at the same airport. One runway surface performed well while the other exhibited a lack of resistance to cyclic shear stress under heavy aircraft braking. Both runways had the same hydrated lime filler and coarse aggregate source. The fine aggregate (dust) used to manufacture the two runway surfaces was obtained from two different basalt quarries. The dust associated with the poorly performing asphalt contained a potentially detrimental clay mineral (Hisingerite). It was subsequently determined that the crude oil used to manufacture the feedstock for the acid-modified binder also changed at the transition from one runway to the other. The changes in dust and binder were confounded. A combination of viscosity testing and performance-based multiple stress creep recovery (MSCR) testing determined that the two runway binders responded significantly differently to shear stress and aged differently with sample storage time. The differences were magnified at higher temperatures. Further, mastic samples were manufactured from binder associated with both feedstocks, in combination with dust from both quarries. MSCR testing of mastic indicated that the dust containing significant Hisingerite had no adverse impact on the mastic response to shear stress. The change in binder feedstock was concluded to be the root cause of the lack of resistance to cyclic shear stress observed in one runway surface. This occurred despite all batches of binder meeting the viscosity-based Australian specification for paving grade bitumen. The specification has no mechanism to prevent similar changes in bitumen feedstock affecting airport bitumen performance in the future. Incorporating performance-based testing in the Australian bitumen specification is recommended.     

A continuum damage model for asphalt cement and asphalt mastic fatigue

An analytical model is developed for the mechanical degradation of asphalt cement and mastic under repeated loading. The model is derived by applying the strain decomposition principle to consider linear viscoelastic, nonlinear viscoelastic, and damage mechanisms. The experimental processes to isolate the behaviors and the analytical functions used to model each are described. It is found that the Schapery type damage approach is capable of modeling the fatigue process of these materials once appropriate consideration is taken for their nonlinear viscoelastic responses. Fatigue in asphalt mastics is also found to occur due to physical damage occurring in the asphalt cement.