Effects of loading waveforms on rock damage using particle simulation method

The particle simulation method is used to study the effects of loading waveforms （i.e. square, sinusoidal and triangle waveforms） on rock damage at mesoscopic scale. Then some influencing factors on rock damage at the mesoscopic scale, such as loading frequency, stress amplitude, mean stress, confining pressure and loading sequence, are also investigated with sinusoidal waveform in detail. The related numerical results have demonstrated that： 1） the loading waveform has a certain effect on rock failure processes. The square waveform has the most damage within these waveforms, while the triangle waveform has less damage than sinusoidal waveform. In each cycle, the number of microscopic cracks increases in the loading stage, while it keeps nearly constant in the unloading stage. 2） The loading frequency, stress amplitude, mean stress, confining pressure and loading sequence have considerable effects on rock damage subjected to cyclic loading. The higher the loading frequency, stress amplitude and mean stress, the greater the damage the rock accumulated; in contrast, the lower the confining pressure, the greater the damage the rock has accumulated. 3） There is a threshold value of mean stress and stress amplitude, below which no further damage accumulated after the first few cycle loadings. 4） The high-to-low loading sequence has more damage than the low-to-high loading sequence, suggesting that the rock damage is loading-path dependent.

Fatigue test setups and analysis methods for asphalt mixture: A state-of-the-art review

Fatigue performance evaluation on asphalt mixture provides an essential reference for asphalt mixture design and pavement structure design.Laboratory fatigue test has been widely used by researchers and engineers to assess the fatigue performance of asphalt mixture,due to its low cost,high efficiency,and strong operability.To ensure performance assessment reliability,fatigue test operated in the laboratory needs to simulate the loading and environmental conditions occurring in the field asphalt layer.As a result,loading setups in laboratory fatigue tests,including loading mode,loading frequency,loading waveform,temperature,and the controlled mode,have been carefully devised by researchers.This paper reviews the above common setups in fatigue tests,which aims to illustrate the classical and latest considerations as well as ideas proposed by researchers for improving fatigue test procedures.As fatigue response data of asphalt mixture is measured from fatigue test,an analysis method is required to process the data and identify fatigue behaviors of the material.Presently,the frequently-used fatigue data analysis methods include the fatigue life model,stiffness-modulus-based method,energy-based method,and viscoelastic continuum damage(VECD)method.This paper also provides a review survey on the main concepts,indicators,and models included in those methods to facilitate their applications.Meanwhile,the latest research progress and outputs related to the four methods are also introduced and discussed to reveal the state-of-the-art developments in this research area.