Investigating nonlinear fatigue damage accumulation of asphalt binders considering loading sequence effect

Abstract

The fatigue damage accumulation of asphalt materials under variable amplitude loading exhibits an obvious nonlinear characteristic. The traditional Miner’s linear fatigue damage accumulation rule fails to characterize the nonlinear fatigue damage accumulation (NLFDA) of the asphalt binders under different variable amplitude loading sequences. This study aims to develop an NLFDA model considering the loading sequence effect for accurately characterizing the effect of different loading sequences on the fatigue damage accumulation of asphalt binders. The fatigue damage of asphalt binders was characterized using dissipated pseudo strain energy (DPSE), and the fatigue damage accumulation laws of the asphalt binders under constant amplitude loading were analyzed by carrying out the stress-controlled constant amplitude fatigue tests of asphalt binders. The fatigue damage accumulation laws of the asphalt binders under variable amplitude loading were analyzed by carrying out the stress-controlled variable amplitude fatigue tests of asphalt binders under the loading sequences of low-high and high-low. The NLFDA model considering the loading sequence effect was developed using the damage equivalent criterion to investigate the effect of loading sequence on the fatigue damage accumulation. This study concludes that the fatigue damage of the asphalt binders under stress-controlled model exhibits an nonlinear evolution trend, which increase slowly initially and then increase sharply. The fatigue damage of asphalt binders under constant amplitude loading accumulates linearly obeying the Miner’s rule, and the cumulative fatigue life fractions are equal to one. The fatigue damage of asphalt binders under variable amplitude loading does not obey the Miner’s rule and accumulates nonlinearly. The accumulative fatigue life of asphalt binders under the variable amplitude loading sequences of low-high and high-low increases and decreases with the increasing first life fraction, respectively. The corresponding cumulative fatigue life fractions are greater than one and less than one, respectively. The developed NLFDA model can address the defects of Miner's rule and can effectively characterize the effect of variable amplitude loading sequence on the fatigue damage accumulation of the asphalt binders. 变幅加载下沥青的疲劳损伤累积具有明显的非线性特征，传统的Miner’s线性疲劳损伤累积准则无法表征不同变幅加载次序下沥青的非线性疲劳损伤累积(NLFDA)。该研究旨在建立考虑加载次序影响的NLFDA模型，准确表征加载次序对沥青疲劳损伤累积的影响。通过开展应力控制的沥青恒幅加载疲劳试验，采用耗散伪应变能(DPSE)表征沥青疲劳损伤，分析恒幅加载下沥青的疲劳损伤累积规律；采用低-高和高-低两种加载次序，开展应力控制的沥青变幅加载疲劳试验，分析变幅加载下沥青的疲劳损伤累积规律；基于损伤等效准则，建立考虑加载次序影响的NLFDA模型，分析加载次序对疲劳损伤累积的影响。结果表明：应力控制模式下的沥青疲劳损伤，呈先缓慢后急剧的非线性增加演化趋势；恒幅加载下沥青疲劳损伤服从Miner’s准则发生线性累积，且累积寿命分数等于1；变幅加载下沥青疲劳损伤不服从Miner’s准则而发生非线性累积。低-高和高-低变幅加载次序下，沥青累积疲劳寿命随一级寿命分数的增大而分别增加和减小，累积寿命分数分别大于1和小于1；建立的NLFDA模型可克服Miner’s准则缺陷，并较为准确地表征加载次序对沥青疲劳损伤累积的影响。