Concept and Development of an Accelerated Repeated Rolling Wheel Load Simulator (ARROWS) for Fatigue Performance Characterization of Asphalt Mixture.

Fatigue performance is one of the most important properties that affect the service life of asphalt mixture. Many fatigue test methods have been developed to evaluate the fatigue performance in the lab. Although these methods have contributed a lot to the fatigue performance evaluation and the development of fatigue related theory and model, their limitations should not be ignored. This paper starts by characterizing the stress state in asphalt pavement under a rolling wheel load. After that, a literature survey focusing on the experimental methods for fatigue performance evaluation is conducted. The working mechanism, applications, benefits, and limitations of each method are summarized. The literature survey results reveal that most of the lab test methods primarily focus on the fatigue performance of asphalt mixture on a material level without considering the effects of pavement structure. In addition, the stress state in the lab samples and the loading speed differ from those of asphalt mixture under rolling wheel tire load. To address these limitations, this paper proposes the concept of an innovative lab fatigue test device named Accelerated Repeated Rolling Wheel Load Simulator (ARROWS). The motivation, concept, and working mechanism of the ARROWS are introduced later in this paper. The ARROWS, which is under construction, is expected to be a feasible and effective method to simulate the repeated roll wheel load in the laboratory.

Analysis of the mechanical effects of defect shape on damage evolution of articular cartilage under rolling load.

To study the mechanical effects of defect shape on the damage evolution of knee cartilage and find the causes of fragments, so as to obtain damage evolution rules and determine the most appropriate shape used in a clinical repair. A porous viscoelasticity fiber-reinforced 2D numerical model with different micro-defect shapes was established which considered the depth-dependent Young's modulus, fiber distribution, porosity and permeability. The stress-strain relationship, interstitial hydraulic and interstitial flow velocity was obtained under rolling load. The results showed that damage developed at the bottom corner of the defect, preferentially deep within the cartilage tangential to the fibers direction, and then extended to the surface along adjacent fibers, finally forming fragments. In the early stages of damage, the shear stress and interstitial flow velocity within cartilage with a rectangular cross-sectional defect were the lowest, while interstitial hydraulic pressure was the highest, followed by 100° trapezoid and semicircle, and finally 80° trapezoid defects. In the later stage of damage, the results were very similar. The shear strain, interstitial flow velocity and interstitial hydraulic pressure decreased with increasing defect depth. Therefore, defect shape only affected damage evolution in the early stages. The fragments in cartilage were the result of the damage evolution which sizes were correlated with the initial defect depth. The damage velocity of cartilage with a rectangular section-incision was the slowest. Finally, we concluded that cylindrical incisions are optimal in clinical surgery. These results provide a theoretical basis for the clinical interpretation of pathological degeneration and repair therapy.