Speaker
Description
We explore experimentally and computationally an unconventional class of fractures in elastomers: sideways cracks. Under certain conditions, a crack propagates in a (sideways) direction parallel to the loading direction rather than perpendicularly in the (forward) direction of the notch. Then, the crack arrests, and the material ahead of the crack can be further deformed enabling giant stretchability. This fracture mode results from higher resistance to propagation perpendicular to the principal stretch direction, driven by deformation-induced anisotropy. Our research efforts show that the tendency of a crack to propagate sideways in the two components of Elastosil P7670 increases with the degree of cross-linking. We show that fracture anisotropy can be modulated during the synthesis of the polymer through the mixing ratio of the raw phases. To assist the investigations, we construct a novel phase-field model for sideways fracture where the critical energy release rate is related to the crosslinking degree. Unlike existing approaches in the literature, we propose a phenomenological model that integrates deformation-induced fracture anisotropy as the fundamental mechanism driving lateral cracking. Our approach renders a crack surface density (γ) unaltered and introduces an anisotropic critical energy release rate in the format of a material function Gc = Gc (F, ϕ), with F and ϕ deformation gradient and damage order parameter, respectively. Eventually, we propose a roadmap with composite soft structures with low and highly crosslinked phases that allow for control over fracture, arresting and/or directing the fracture. The smart combination of the phases enables soft structures with enhanced fracture tolerance and reduced stiffness.
References:
M.A. Moreno-Mateos, P. Steinmann. “Crosslinking degree variations enable programming and controlling soft fracture via sideways cracking”. Accepted, In Press in Npj Computational Materials.
