Parag Ravindran

Modelling Sand–Asphalt Mixtures Within a Thermodynamic Framework: Theory and Application to Torsion Experiments

Sand–asphalt mixtures are difficult to model, partly due to their composition and partly due to the complex interplay among their constituents. This work is concerned with the development of an anisotropic model to describe the nonlinear behaviour of sand–asphalt mixtures. A general thermodynamic framework is used, which allows for the material to have multiple natural configurations corresponding to its underlying structure. The evolution of the natural configuration takes place in a thermodynamically consistent manner. The model developed is corroborated using experimental results published by Ravindran et al. (2007a,b) on torsion tests of sand–asphalt specimens over a range of conditions.

Steady free surface flow of a fluid-solid mixture down an inclined plane

The present work is an extension of the investigations performed by Massoudi and Anand (2001). The free surface flow problem is studied here. Numerical solutions for steady free surface flow of a solid-fluid mixture down an inclined plane are presented. The problem is formulated using the mixture theory framework. The resulting set of three coupled nonlinear differential equations is nondimensionalized. A parametric study is conducted to understand the influence of the dimensionless numbers on the velocity and volume fraction. The maximum fluid velocity is found to decrease with increase in the ratio of the drag force to the viscous forces within the fluid phase (D1). The fluid phase velocity was found to decrease with increase in the ratio of the drag force to viscous force within the solid component (D2), and the corresponding solid phase velocity was found to increase.

An Experimental Investigation into the Influence of Fillers on the Development of Normal Stresses and Stress Relaxation in Asphalt Mixtures Due to Torsion

This study documents the measurement of normal stresses and stress relaxation in sand-asphalt mixtures fabricated with different fillers and asphalts during torsion. Hydrated lime and limestone fillers and asphalts graded as PG64-22 and AC-30 (from Sinclair (Wyoming), Crown (Nevada), and Crown (Canada)) are used in the fabrication of the sand-asphalt mixtures. The specimens are tested in a torsional rheometer. The experimental results clearly show that the normal stresses that are developed are quite significant even for specimens tested at very low rotational rates. Also, asphalts from different sources show differences in peak normal stresses and in their relaxation pattern. The measurement of significant normal stresses is a reflection of the nonlinear character of the material and warrants the development of nonlinear constitutive models for describing their behavior.

A Constitutive Model for Soft Tissue and its Application to a Boundary Value Problem

Mechanical loading induces changes in the structure and function of soft tissue. Growth and remodeling results from the production and removal of constituents. We consider a tissue constituted of elastin and collagen. The collagen turns over at a much higher rate than elastin. In this work we propose a two-constituent, constrained mixture model for this soft tissue. One constituent is modeled as a viscoelastic material and the other as an elastic material. It is assumed that the collagen turns over depending on the stress applied and the elastin does not turn over. The standard mixture theory approach is followed and the balance equations are set-up. The model is studied in simple uni-axial loading to test its efficacy.Copyright

Investigation on the Influence of Air Voids and Active Filler on the Mechanical Response of Bitumen Stabilized Material

AbstractCold in-place recycling technology for reclaimed material in pavement rehabilitation holds promise as a solution to resource scarcity. This paper reports results of a systematic experimenta...

Evolution of energy dissipation during four-point bending of bituminous mixtures

In this investigation, the fatigue life of bituminous mixtures is characterised using the four-point bending test. Two sets of bituminous concrete samples, one produced with unmodified binder and other with plastomer-modified binder, are subjected to repeated strain-controlled sinusoidal loading at 10 Hz frequency and 20°C. The test is conducted for three different strain amplitudes of 200, 400 and 600 microstrain and the corresponding stress and strain data are collected at 1/1000 second interval. In the first approach, these data are used to calculate total energy dissipation. The dissipation due to damage is determined by separating viscoelastic dissipation from the total dissipation. For this purpose, a linear viscoelastic model is used. In the second approach, the discontinuity in the evolution of phase lag determined from the stress–strain plot is taken as the onset of fatigue damage. The fatigue failure, as quantified by these two approaches, was found to be closer to the fatigue life computed using energy ratio method.

Aging in Soft Tissues: Influence of Chemical Reactions on Mechanical Response

Aging of soft tissues occurs through various mechanisms, which involve biochemical reactions, like glycation, oxidation and calcification of proteins in the extracellular matrix of the soft tissue. Aging leads to changes in the microstructure of the soft tissues which results in changes in its mechanical behavior. In this paper, a mixture theory based model that is thermodynamically consistent and applicable for chemically reacting systems is developed. The tissue (elastin) is modeled as a viscoelastic material. The model is simulated for uni-axial loading to study the effect of chemical reactions occurring in the tissue (elastin) on its mechanical response.Copyright