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 A jargon-free introduction to what we do 

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Mechanics of squishy sticky things

Engineering traditionally deals with materials that are ultra stiff. Steel and Aluminium both have moduli in the range of 100 GPa. Most plastics, commonly considered 'flexible', still have moduli well over 100 MPa. Materials like lightly frozen butter, which has a modulus of about an MPa, may not seem very useful to the engineer.

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Yet, in recent times, a very large number of applications have emerged where soft materials (with moduli well below an MPa) have found their niche. Soft robotics and stretchable electronics are two areas that have seen especially prolific and enthusiastic applications of ultra-soft materials. Models and ideas associated with synthetic soft materials have also proved useful in understanding the role of mechanics in biological processes.

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The spurt of interest in soft materials is undoubtedly aided by two parallel technological developments. First is the rapid progress in 3D printing technology which allows us to conceptualise functional engineering designs involving shapes far removed from the usual regular ones that we traditionally use. Secondly, polymer scientists have come up with clever techniques to synthesise ultra-soft materials with designer properties. Examples are materials like hydrogels constituted mostly of water molecules trapped within macromolecular cages. We also have several elastomeric materials available today where the molecules are arranged in pre-designed ways to impart very specific gradation in mechanical properties. Not only are these materials soft, they often have unique capabilities to respond to external stimuli like humidity or pH of their surroundings and electric fields.

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Modelling the deformation behaviour of soft materials on a computer has thrown up new challenges. Since they have very low values of stiffness, the luxury of linear elasticity is no longer available to us --- even under very small forces, the deformations can turn out to be very large and the non-linear behaviour of the material inevitably manifests itself. In fact, often, gradually increasing forces do not necessarily lead to smoothly evolving deformations. Sudden, large adjustments to the shape of a soft solid body often throws simulations off guard.

 

Moreover, soft solids often are influenced by their surroundings in ways that their stiffer counterparts are not. This makes the surrounding pH, humidity, electric or magnetic fields as much a player in the deformation process as the applied mechanical

forces. Forces may also arise because the solid is 'growing' (as biological tissues do) or surface tension --- a property we associate generally with fluids --- competes with bulk elasticity.

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We try to computationally model deformation of soft solids under various multi-physical situations while being mindful of their 

quirks. 

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Understanding material behaviour in silico

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We specialise in building and implementing models for material behaviour in the computer. This means that we devise mathematical equations that determine how a particular material deforms and breaks when subjected to forces so that, in the computer, the material behaves as closely as possible to a real one. When the models are correct, they allow us to understand things about the material in ways that experiments cannot.

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We have built, used, and supplemented models for various kinds of materials --- metals, polymers, elastomers, composites, plant stems, brain tissues!! Also look at interfaces where two different materials meet. 

 

 The material or material systems are often subjected to mechanical loads that vary slowly with time. But we also look at situations where the loads vary very fast or when the loads are not of mechanical origin at all. 

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Modelling materials leads us to look at materials at different levels. Clues to their deformation behaviour are often found only if we view them at the microscopic level where they appear as discrete systems of interconnected atoms. Sometimes, treating the material as a continuum suffices. Depending on how we look at the material, models that are built or used, also change.

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Tracking cracks

We are also interested in how materials fail. Failure generally is a inevitability, a eventual last and quick step in the life of a deforming material over which a crack starting from somewhere deep inside the material rips through its volume. However, models for predicting the path that the crack will take are far from perfect.  

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Sometimes a good engineering approach is to accept that a material is infested with cracks and our task is to ensure that none of them grow. Also, often, we more or less know the path that a crack will take if it grows and our job is to estimate how much energy we need to supply so that it does.

 

The hardest problem is when you have no idea about the path a crack will take and still want to figure out how much energy you can pump into a material before it splits into pieces.  We work on this problem using various methods that others have suggested. Unfortunately, none of them are universal and every situation calls for a different strategy. 

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