No abstract

No abstract

No abstract

No abstract

No abstract

A B S T R A C T This study investigates the fatigue characteristics of typical bituminous materials used in road applications. Fatigue testing was performed in a four-point bending beam test apparatus under controlled strain and stress conditions. Fatigue life was defined using the classical approach as the number of cycles, N f , to 50% reduction in the initial stiffness modulus. It has also been defined in terms of macro-crack initiation, N 1 . A different approach, based on the linear reduction in stiffness during a particular stage of a fatigue test, was introduced to define a damage parameter, and the evolution of this damage parameter with number of cycles was used to characterize fatigue life. Furthermore, refinements to the linear damage model were introduced to take into account the difference in the evolution of dissipated energy between controlled strain and stress testing modes. These modifications have enabled the identification of a unique fatigue damage rate for both controlled strain and stress test modes.Keywords bituminous materials; dissipated energy; fatigue life; four-point bending test; linear damage model. N O M E N C L A T U R ED = damage parameter E = complex stiffness modulus (referred as stiffness) E 0 = initial stiffness E 00 = intercept of the fitted line for the stiffness data N = number of (load) cycles N f = number of cycles to 50% stiffness reduction N 1 = number of cycles to macro-crack initiation R n = energy ratio W = dissipated energy W 00 = intercept of the fitted line for the dissipated energy data ε n = strain at the n-cycle σ n = stress at the n-cycle φ n = phase angle at the n-cycle

No abstract

This research examines the hysteresis friction of a sliding elastomer on various types of stone surfaces. The hysteresis friction is calculated with an analytical model that considers the energy spent by the local deformation of the rubber due to surface asperities of the stone surface. By establishing the fractal character of the stone surfaces, one can account for the contribution to rubber friction of stone roughness at different length scales. A high-resolution surface profilometer is used to calculate the three main surface descriptors and the minimal length scale that can contribute to hysteresis friction. The rubber is treated as a Zener visco-elastic material model. Modeling of the contact between the elastomer and the stone surface is based on the analytical model of Klüppel and Heinrich, which is a generalization of the Greenwood and Williamson theory of contact between spheres that are statistically distributed about a mean plane. The results show that this method can be used in order to characterize in an elegant manner the surface morphology of various stone surfaces and to quantify the friction coefficient of sliding rubber as a function of surface roughness, load, and speed.