Dr.-Ing. Kumar, Paras

SoftFrac will revolutionise geometrically nonlinear fracture mechanics of soft materials (in short soft fracture) by capitalising on configurational mechanics, an unconventional continuum formulation that I helped shaping over the past decades. Mastering soft fracture will result in disruptive progress in designing the failure resilience of soft devices, i.e. soft robotics, stretchable electronics and tissue engineering applications. Soft materials are challenging since they can display moduli as low as only a few kPa, thus allowing for extremely large deformations. Geometrically linear fracture mechanics is well established, nevertheless not applicable for soft fracture given the over-restrictive assumptions of infinitesimal deformations. The appropriate geometrically nonlinear, finite deformation counterpart is, however, still in its infancy. By combining innovative data-driven/data-adaptive constitutive modelling with novel configurational-force-driven fracture onset and crack propagation, I will overcome the fundamental obstacles to date preventing significant progress in soft fracture. I propose three interwoven research Threads jointly addressing challenging theoretical, computational and experimental problems in soft fracture. The theoretical Thread establishes a new constitutive modelling ansatz for soft in/elastic materials, and develops the transformational configurational fracture approach. The computational Thread provides the associated novel algorithmic setting and delivers high-fidelity discretisation schemes to numerically follow crack propagation driven by accurately determined configurational forces. The experimental Thread generates and analyses comprehensive experimental data of soft materials and their geometrically nonlinear fracture for properly calibrating and validating the theoretical and computational developments. Ultimately, SoftFrac, for the first time, opens up new horizons for holistically exploring the nascent field soft fracture.

The mechanical properties and the fracture toughness of polymers can be increased by adding silica nanoparticles. This increase is mainly caused by the development of localized shear bands, initiated by the stress concentrations due to the silica particles. Other mechanisms responsible for the observed toughening are debonding of the particles and void growth in the matrix material. The particular mechanisms depend strongly on the structure and chemistry of the polymers and will be analysed for two classes of polymer-silica composites, with highly crosslinked thermosets or with biodegradable nestled fibres (cellulose, aramid) as matrix materials.

The aim of the project is to study the influence of different mesoscopic parameters, as particle volume fraction, on the macroscopic fracture properties of nanoparticle reinforced polymers.