Research On Cumulative Fatigue Damage Of Asphalt Mixture And Asphalt Layer Based On Multi-level Amplitude Loading

Fatigue damage which is one of the (destructive forms)of the asphalt pavent is also animportant issue to consider for the design of the asphalt pavent structure. Asphalt mixture asthe main building material of asphalt pavent, studying its process of cumulative fatiguedamage and predicting the fatigue life under the traffic loading is an important way to studyasphalt pavent fatigue damage and destruction. And it is a key issue which needs to be solvedThis project is part of "the study about the random accumulated fatigue damage of asphaltpavent", which is supported by the key program of national natural science foundation (GrantNo.51038004). Through four-point bending beam fatigue test under different loading ways, itreveals each variation of asphalt mixture performance paraters, carries out nonlinear fatiguedamage of asphalt mixture based on the stiffness modulus decay associated with the loadinghistory and order, and has important scientific reference value for improving the existingasphalt pavent fatigue design.Through four-point bending load beam fatigue test of a single-stage load under four kinds ofstrain levels, this paper proposes a thod to determine the initial stiffness modulus and failurecriterion. According to this, this paper which gives the prediction equation of the expectedfatigue life of asphalt mix under single-stage load related to stiffness modulus and strain andalso analyzes the attenuation regulation of the flexural tensile stiffness modulus under differentstrain levels, establishes the fatigue cumulative damage model of power function which isbased on load tis, load size and stiffness modulus. By this the nonlinear characteristicalevolution of asphalt mixture fatigue damage has been determined.Through the fatigue test under the multi-level amplitude load of different loading thods, thedecay law of indicators related to fatigue damage, such as,the flexural tensile stiffness modulusand energy dissipation change rate under varying load size, different load tis and different loadorder is obtained. Previous fatigue damage accumulation model can not accurately fit thecumulative fatigue damage of the asphalt mixture under multilevel loads, so there is a bigdifference between the predicted fatigue life and experintal results. Based on these, this paperproposes and establishes a new prediction equation of the fatigue life associated with the loadhistory and load order, whose prediction results are more accurate than the prediction model ofthe fatigue life of all ti, which suggests that using load history and load sequence as fatiguedamage parater has more advantages. Using digital speckle correlation asurent system (DSCM) and the program based on theMatlab platform combined with the nurical calculate thod of the fractal theory to study thedevelopnt law of crack which is macro reflect of fatigue damage accumulation in asphaltmixture under the multi-stage loading, reveals the change of the cumulative fatigue damagepathway when load converses. At the sa ti, through changing the proportion of low and highstrain level load tis, we conclude that asphalt mixture have "training effect" under low-highload mode. According to the research above, a reasonable explanation for the delayingphenonon of the fatigue damage is got when multi-level loads convert. We deeply analyze thefatigue damage accumulation law of asphalt mixture under multi-stage loads, and study theasphalt mixture damage based on the accumulated fatigue damage. Study shows that the loadhistory and load order have a great effect on the asphalt mixture fatigue damage; we try toestablish a new evaluation system on the basis of the nonlinear accumulated fatigue damagewhich can reflect the current situation injuries, loading history and load order. Case analysisshows that it can better reflect the actual fatigue damage of asphalt pavent layer than theexisting evaluation system based on Miner linear criteria.The results of this study can help people get a better understanding of the fatigue damageaccumulation laws of asphalt pavent under loads, and lay the foundation for the establishnt ofthe controlling indicator of the asphalt layers damage system using tensile strain at the end oflayer upon layer, which has great significance for perfecting the fatigue design thod of asphaltpavent and improving the design level for the durability of asphalt layer.