Hydraulic fracture and toughening of a brittle layer bonded to a hydrogel
By Alessandro Lucantonio from SISSA
And
Biological crawling and swimming micro-organisms: a case study in shape control for locomotion purposes
By Giovanni Noselli from SISSA
Date: July 3rd 2015, Friday, 12:00 h
Location: Room 212, Building C2, Campus Nord UPC
Detailed information can be found at the following link: https://www.lacan.upc.edu/node/720
Alessandro Lucantonio:
Brittle materials propagate opening cracks under tension. When stress increases beyond a critical magnitude, then quasi-static crack propagation becomes unstable. In the presence of several pre-cracks, a brittle material always propagates only the weakest crack, leading to catastrophic failure. Here, we show that all these features of brittle fracture are fundamentally modified when the material susceptible to cracking is bonded to a hydrogel, a common situation in biological tissues. In the presence of the hydrogel, the brittle material can fracture in compression and can hydraulically resist cracking in tension. Furthermore, the poroelastic coupling regularizes the crack dynamics and enhances material toughness by promoting multiple cracking.
Giovanni Noselli:
Bio-‐inspired motility is a fascinating topic of active current research, with a significant potential for new technological applications. Cells and unicellular organisms provide striking examples of microscopic selfpropelled objects, with length scales in the range from one to one-‐hundred microns, that are able to move freely inside the human body. Learning these skills from biological organisms requires, in particular, that we learn how to move and control continuously deformable objects. Just like their biological templates, devices capable of large elastic deformations can exhibit superior dexterity and manoeuvrability than more standard robotic constructs based on the articulation of few rigid links. This is, in fact, an instance of soft robotics, a new paradigm in robotic science, where novel designs are inspired by the study of how animals exploit soft materials to move effectively in complex and unpredictable natural environments. We will report on some recent case studies on biological and bio-‐inspired locomotion in which, starting from the observation and the mathematical modelling of a motile organism (unicellular swimmers, snails, earthworms), we distill some of the key mechanisms at work in the biological templates with the aim of reproducing them in artificial bio-‐inspired devices.