Date of Award
Program or Major
Doctor of Philosophy
Jo Sias Daniel
In this research, an existing uniaxial constitutive model has been extended to flexural loading mode and a new approach to predict fatigue behavior is proposed. The proposed methodology involves dynamic modulus testing to obtain viscoelastic properties and subsequent fatigue testing. Several asphalt concrete beams were tested according to the proposed methodology. The analysis of data indicates that there exists a unique relationship between the flexural pseudostiffness and amount of damage in the specimen. To verify the accuracy of the fatigue prediction model, fatigue tests were conducted on specimens that were not part of preliminary analysis. The fatigue life predictions made were comparable to actual measurements. The proposed methodology offers advantages like considerable savings in testing time and materials when compared to the existing AASHTO protocol.
An alternative approach for the determination of the fatigue endurance limit of asphalt concrete using the elastic-viscoelastic correspondence principle is proposed. The proposed testing procedure consists of applying stress or strain blocks of loading starting from low to high amplitude. The development of loops and changes in stress-pseudostrain loops is used to detect damage in the specimen. To verify the proposed methodology, tests were conducted under different modes (stress and strain controlled, uniaxial and flexure). When compared to strain controlled mode, the stress controlled mode required shorter testing time, had less noise and offered better control during testing.
The third part of this research is to study the effect of mode of loading on viscoelastic properties and damage characteristics. Several specimens were tested under uniaxial, biaxial and flexure mode to obtain fingerprints of viscoelastic and damage properties. It was found that viscoelastic and damage properties are dependent on loading mode and testing frequency. A systematic variation of viscoelastic properties was found between different loading modes. Several frequency dependent modular ratios are proposed which, in principle, can be used as modal correction factors. It was observed that the specimen undergoes damage at a faster rate under uniaxial mode when compared to flexure loading mode. At a given value of normalized pseudostiffness, the damage parameter ratio remained approximately same and is a function of material properties.
Krishna Swamy, Aravind, "Evaluating mode of loading effect and laboratory fatigue performance of asphalt concrete using viscoelastic continuum damage mechanics" (2011). Doctoral Dissertations. 571.