Mechanical and Civil Engineering Seminar

Mechanical and Civil Engineering Seminar Series

Title: Modeling Ductile and Brittle Fracture of Polycrystals

Abstract:

Ceramics and metallic alloys, at the micro-scale, are composed of grains whose crystallographic nature induce a local anisotropy of the micromechanical properties of these heterogeneous materials. A fundamental understanding of anisotropic elasto-plastic and fracture mechanisms and their link with macroscopic strength and toughness properties of polycrystalline materials will open the path to the design of better performing microstructures. In this talk, I will present recent developments in micromechanical modeling of ductile and brittle fracture of engineering and model materials. I will first focus my presentation on the derivation of a ductile fracture model accounting for the anisotropic character of crystal plasticity. Stressing the need for mesh-dependency regularization in the fracture-induced softening regime, I will present numerical results of ductile crack growth in single- and poly-crystals. Then, shifting to brittle materials, I will show how models based on a phase-field representation of cracks can be improved in order to account for the fracture anisotropy of crystals. First, a new model based on multiple phase-field variables is proposed in order to capture cracks along several cleavage planes. Then, another approach based on the coupling between small-scale yielding at the crack tip and phase-field brittle fracture is introduced to study the fracture anisotropy of quasi-brittle materials. I will conclude with some thoughts on how these models can be calibrated and validated with experiments before being applied to guide the design of new materials.

Bio:

Jean-Michel Scherer is a postdoctoral scholar in the Bhattacharya group at the California Institute of Technology. He received his M.Sc. from Mines Nancy (Nancy, France) in 2017 and his Ph.D. from Mines ParisTech (Paris, France) in 2020 for research conducted at the French Alternative Energies and Atomic Energy Commission (CEA). Before joining Caltech in 2022, Jean-Michel was as postdoctoral scholar at École Polytechnique (Palaiseau, France) and at École des Ponts ParisTech (Champs-sur-Marne, France). His research interests focus on the micromechanical behavior of metallic and ceramic materials. At the interface of theoretical modeling, numerical simulation and small-scale experimental techniques, he studies the interactions between the material microstructure and mechanisms of plasticity and fracture in order to design new materials with increased mechanical properties.

NOTE: At this time, in-person Mechanical and Civil Engineering Lectures are open to all Caltech students/staff/faculty/visitors.