IMX Colloquium - Defects in cracks and contact: enhancing toughness and suppressing wetting

Cracks can destroy structures. Contacts drive countless industrial processes. Though these seem very different, the underlying mechanics are surprisingly similar: stress builds up and diverges at a single moving point — the tip of a crack or the edge of a forming contact — driven by external forces. These regions are notoriously hard to study because they’re obscured within the surrounding material. Using high-speed 3D imaging, we capture these dynamics in real time. Our work reveals that tiny defects and random noise strongly influence both crack growth and contact formation. Two case studies highlight this: how geometry affects toughness in brittle hydrogels, and how defects shape the formation of contacts. Despite their differences, both systems show universal behaviors that emerge from these local, nonlinear dynamics. We’ll conclude with a demonstration of how these insights can be applied — from boosting material toughness to precisely manipulating liquid droplets.

Bio: Kolinski heads the Engineering Mechanics of Soft Interfaces laboratory in the Institute of Mechanical Engineering in STI at EPFL, where he currently mentors five PhD students. The group’s research activities span the domain of continuum mechanics, with research into liquid-solid wetting, mechanics of viscoelastic solids and fracture of hydrogels. With colleagues, Kolinski organized two international workshops in 2023 and 2024 on fracture mechanics, at CECAM in Lausanne and at PCTS in Princeton. The impact of the group’s research can be perceived from publications in leading journals, international, interdisciplinary collaborations with leading scholars, several grants from Innosuisse and SNSF, invited lectures and awards to the group’s students on the international stage. Prior to starting his group at EPFL in 2017, Kolinski was a Fulbright fellow at the Hebrew University of Jerusalem in the Physics department, where he worked on dynamic fracture in hydrogels. Kolinski defended his PhD thesis on the role of air in droplet impact on a smooth solid surface at Harvard in 2013, with support from the NSF GRFP and NDSEG fellowships.