Mechanics of Time Dependent Materials Laboratory

The primary focus is on understanding the time dependent mechanical response of materials to mechanical, chemical and thermal loads. In essence we develop relations between quantities that describe the deformation and measures of the stress in a three dimensional setting in a thermodynamically consistent manner. Viscoelastic materials are of interest in variety of settings. We primarily work on modeling of polymer composites, biological tissues and sand asphalt mixtures.

Focus Area: Modeling of Soft Tissues

The goal here is to develop a class of constitutive relations within a thermodynamic framework to model the mechanical response of soft tissues when subjected to external stimuli (mechanical and chemical), and to validate it with experimental data from the literature. The external stimuli drives growth, remodeling and degradation. A phenomenological model, that can describe the growth and remodeling of soft tissue, within the framework of constrained mixtures has been developed. The model developed is applied to some simple boundary value problems. The assumption is that the production and removal of collagen is responsible for growth and remodeling of the tissue. Work is under way to extend the applicability of the model.

Focus Area: Modeling of Polymeric Composites

Robust models for polymeric composites are great interest in engineering. In this context, a study was undertaken to understand the coupling between mechanical loading and thermal response. Thermomechanical coupling offers the scope to non-invasively determine material characteristics. A model was developed and calibrated using available experimental data. Qualitative agreement was obtained between model predictions and experimental data for different ply orientations. The model predicts that temperature rise in glass-epoxy composites depends on the elongation rate.

Another area of interest within the context of modeling polymeric viscoelastic material, is the role of inhomogeneity and the possibility of approximating such materials by a homogenized model.

We have also studied the response of carbon fibre reinforced epoxy composites to cyclic loading. The response in the direction transverse to the loading direction is an important indicator of damage under certain conditions.

In another interesting study a model was developed and used to the study the mechanical response of rubber during vulcanization. The model predicts the expected improvement in the mechanical properties of rubber after vulcanization. Such models are potentially very useful in the tire industry.

Focus Area: Mechanics of Asphalt Based Materials

Asphalt is a widely used engineering material. It has a long history of usage. Asphalt is obtained as by-product of the petroluem refining process and is itself a mixture of several constituents whose composition depends on processing conditions and crude source. The asphalt in the field is mixed with fillers and larger aggregates of different gradations (depending on usage), and put to use for pavement making. The pavement endures large mechanical loads and other challenging environmental conditions. Under these conditions, prediciting its response is a diffcult task. The need for robust models cannot be over-emphasized in the current scenario of limited resourses and environmental constraints. We have developed a nonlinear viscoelastic model within a thermodynamic framework for sand-asphalt mixture.

Currently an area of importance is reclaimed asphalt pavement (RAP) material. Cold Inplace Recycling (CIR) is particularly promising technique due to its environmental friendly nature. We have also attempted to model such materials and understand their performance vis-a-vis traditional asphalt based materials.