A BIT MORE ABOUT OUR WORK

Soft Solids

Soft Solids in Electric fields


Soft materials with very low stiffness (not more than a few kPa) but high dielectric permittivity (relative permittivity above ~4) and high breakdown strength (above about 40 MV/m), can deform, often by large amounts, when placed in a strong electric field. We are performing both sophisticated Finite Element simulations as well as some simple experiments to characterise the performance of devices made with such soft solids. There are several computational challenges involved:

Natural Materials: Plant stems/tall grasses

Plants have evolutionally perfected a microstructure that performs specific structural functions very effectively. For example, tall grasses like bamboo can withstand very high fluctuating wind loads over many many cycles without uprooting or breaking. The microstructure that most of these tall grasses have adopted can be described as a functionally graded composite with a foamy matrix reinforced by short stiff fibres. No synthetic material has a microstructure that fits this description. Is there a good reason to try and emulate this microstructure in engineering materials? This is an unanswered question. To answer this, we first need to figure out how this microstructure helps a plant withstand cyclic bending loads. We are trying to do this through a series of experiments, mechanical characterisation exercises and simulations.

Surface effects in soft solids

Ultra soft solids are a bit like fluids. Surface energies in soft solids are high and effects of strain on surface tension become very important in small sized structures made of these soft materials. For example, a short, soft cylinder may form a meniscus even when it is not loaded. Very small voids in a matrix filled with a soft solid may lead to an overall stiffening. We are computationally exploring a number of problems that involve surface elasticity in soft solids.

Polymers

Polymers are probably the most suitable candidate for ‘designer materials’. Polymer chemists have immense control over architectures of the macromolecules. We are, through Molecular Dynamics and non-linear Finite Element simulations, trying to figure out if molecular architectures can be connected to mechanical properties. The ultimate goal will be to reverse design the architectures that leads to a material with a given combination of mechanical properties. We work with amorphous thermoplastic and thermoset polymers. The work is primarily classified into

Multifunctional Materials

Demands on modern materials are often diverse and contradictory. For instance, aerospace materials need to be stiff, tough, light, thermally conducting, able to withstand lightning strikes and reflect incoming electromagnetic waves. Windshields of cars must be tough, transparent and light. We are looking at a nano-reinforced composites which offer a combination of diverse properties. In fact, combining nano reinforcements like nanoparticles, nanotubes and graphene flakes in an optimal manner can indeed lead to composite materials than can perform a number of functions effectively. We are looking at two specific possibilities:

Failure in metals

Accurate prediction of failure in ductile metals is a long standing technological problem, in spite of the fact that ductile fracture is probably the most studied and understood mode of fracture. We are working on developing computational techniques for predicting yield and failure surfaces of ductile materials under monotonic as well as non-monotonic loading.