Research Projects

Solids with moduli ranging between 10 − 1000 kPa (silicone elastomers and hydrogels are synthetic examples) are generally characterised as ‘soft’. Gel, creams, food products and most biological tissues can be categorised as soft solids. It has long been realised that the mechanics of deformation and failure of such soft materials is fundamentally different from their stiffer counterparts. Soft solids are now being used in varied applications like soft robotics and flexible electronics. Reliable design and deployment of soft solid based applications require a better understanding of and ability to model deformation and failure of these materials. Moreover, mechanics of soft materials is important for understanding many biological problems involving morphogenesis of soft tissues. Models must consider the following: 1. Most soft materials behave as hyperelastic solids, and often are visco-hyperelastic. Moreover, owing to their low stiffness, finite deformations must be taken into account even though the levels of applied forces may be small, rendering their mechanistic descriptions both materially and geometrically non-linear. 2 It has recently been established that surface stresses influence the deformation behaviour of soft solids at the micrometer or even millimeter length scale. This is because, for many soft solids, the elastocapillary length, i.e. the ratio between a surface stress measure γ and the bulk modulus µ, is often large and of the order of characteristic dimensions. Large elastocapillary lengths lead to unusual deformation behaviour. 3. Soft solids often possess very high toughness and are extremely resistant to growth of pre-existing defects. Our objectives in this proposal are the following 1. Develop and demonstrate combined experimental characterisation techniques for bulk and surface elastic properties of soft solids with moduli in the range of 10 − 1000 kPa and failure stretch greater than 5. 2. Develop Finite Element (FE) modelling tools for simulating deformation, fracture and instabilities in soft solids within the framework of large deformation visco-hyperelasticity and incorporating elastocapillarity. 3. Determine suitable failure initiation criteria for soft solids.