Definition of the Time of Fatigue Life and Dynamic Mechanical Properties of Materials of the Contacting Surfaces

The unexpected collapse of engineering structures is often caused by the fatigue phenomenon resulting from degradation of mechanical properties of materials due to multiaxial cyclic loadings. The interpretation of such degradation is a topic of intensive research in multiaxial fatigue. The fatigue strength is commonly evaluated by the equivalent stress based on the shear stress in the octahedral plane. However, the use of this kind of equivalent stress in the multiaxial fatigue criteria has been proven to be inappropriate. The degradation of mechanical properties of materials is dependent on several factors, e.g. the loading path has a strong influence on the fatigue strength. Non-proportional loadings cause higher damage in materials than proportional loadings for the same maximum equivalent stress. The purpose of this work is to study the effect of different multiaxial loadings on the 42CrMo4 steel and to improve the understanding about the relation between the fatigue strength and the sequential loading proportionality. The considered loadings were defined with the same history but with different load sequences and equivalent stress. To implement this work a biaxial servo-hydraulic fatigue machine was used. The fatigue life and crack angle were measured for each specimen. An analysis was made in order to correlate the crack initiation and fatigue life with the theoretical models, some remarks regarding these topics are presented.

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Research on Fractional Derivative Viscoelastic Constitutive Relation of Asphalt Mixture

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.446-449.2560 ◽

2012 ◽

Vol 446-449 ◽

pp. 2560-2566

Author(s):

Hua Yin ◽

Yi Li ◽

Nai Zhou Wang

Keyword(s):

Mechanical Properties ◽

Fractional Derivative ◽

Phase Angle ◽

Constitutive Relation ◽

Viscoelastic Model ◽

Asphalt Mixture ◽

Maxwell Model ◽

Dynamic Mechanical Properties ◽

Dynamic Mechanical ◽

Definition Of

Based on the definition of fractional derivative, the paper proposed a unique new idea to describe the viscoelastic property of asphalt mixture with fractional calculus. According to the SPT (Simple Performance Tests) test results, the dynamic modulus and phase angle of asphalt mixture were determined. The result of the test was fitted with the classical Kelvin model, the Maxwell model, the solid model with three elements, respectively. It showed that the classical viscoelastic model did not simulate the dynamic mechanical properties of asphalt mixture properly. Since the existing constitutive relation cannot describe well the dynamic viscoelastic properties of asphalt mixture, the fractional derivative viscoelastic model with three elements was adopted and its fitting effect analyzed. The result shown a good fitting for the fractional derivative viscoelastic model with three elements, and a few test parameters were required to build the mode. In addition, these simulating parameters were significant in physics. The order  of the fractional derivative has good correlation with the phase angle, incarnating the viscoelastic proportion of asphalt mixture. So the fractional derivative viscoelastic model with three elements can accurately describe the dynamic mechanical properties of asphalt mixture.

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