MechE Seminar: Probing cracks and contact at obscured interfaces with 3D microscopy

Abstract: 

The macroscopic properties of materials and structures are used in the engineering design of myriad systems that are in fact controlled by processes at microscopic scales. Examples include the initiation and propagation of cracks, which govern the ultimate strength of structures, and the dissipation at the edge of an advancing contact line that determines overall fluid motion. These are examples of `propagating singularities,’ where the stress diverges to infinity at the advancing crack or contact front. Fracture and contact processes invoke motion and stress across scales, and are typically obscured by the bulk; as a consequence, such systems are challenging to characterize experimentally. In this talk, I describe how we surmount these challenges with 3D imaging methods at the micro-scale. With these methods, we identify the conditions required for contact formation beneath an impacting droplet, and discover a quantitative connection between crack front geometry and material toughness. I conclude with a discussion of how our observations about fundamental mechanical processes may be used in an engineering context.  



Biography:

Dr. Kolinski studied Applied Mathematics (Sc.M.) and Applied Physics (Ph.D.) at Harvard University under the supervision of L. Mahadevan and Shmuel Rubinstein, completing his thesis on the role of air in droplet impact. After completing his thesis, John moved to the Hebrew University to continue research on interfacial instabilities as a post-doc with Jay Fineberg and Eran Sharon. Currently, Kolinski is a tenure-track assistant professor at EPFL, where his lab probes the microscopic mechanisms governing the mechanical behavior of materials through 3D imaging of cracks and contact lines.