dynamic fracture

World-renowned mechanician, Professor Freund at Brown University passed away on October 3, 2024. He was a member of the US National Academy of Sciences/Engineering and made significant contributions to mechanics research and the scientific community. Moreover, Prof. Fruend mentored many outstanding Ph.D. students including Prof. Yang Wei at Zhejiang University and my mentor Prof. Ares Rosakis at the  California Institute of Technology.  His famous works include two books: Dynamic Fracture Mechanics, Thin Film Materials co-authored with Subra Suresh.

The research — We use x-ray phase contrast imaging (XPCI) to study deformation and fracture of materials under dynamic loading on microsecond and sub-microsecond time scales. For example, we might like to measure the change in pore size distribution of a granular material such as sandstone under impact loading. Answering this question requires us to address theoretical and computational questions of XPCI image interpretation, and also poses an interesting challenge to the experimentalist.

It gives me great pleasure to announce the mini-symposium titled "Characterization and Modeling of Dynamic Fracture of Composites" at the 2021 Mach conference, to be held virtually from April 7 to April 9 2021.

The Mach Conference showcases the state of the art of multiscale research in materials, with an emphasis on advancing the fundamental science and engineering of materials and structures in extreme environments

Conference website: https://machconference.org/

Phase-field models for crack propagation enable the simulation of complex crack patterns without complex and expensive tracking and remeshing as cracks grow. In the setting without inertia, the crack evolution is obtained from a variational energetic starting point, and leads to an equation for the order parameter coupled to elastostatics. Careful mathematical analysis has shown that this is consistent with the Griffith model for fracture. Recent efforts to include inertia in this formulation have replaced elastostatics by elastodynamics.

Overview: The peridynamic formulation is a
spatially nonlocal derivative free model for simulating problems of free crack
propagation.Material points interact through short-range forces and the
formulation allows for discontinuous deformations. Here the short-range forces
are initially elastic and soften beyond a critical relative displacement. We
upscale this peridynamic model to find the macroscopic (a.k.a. small horizon)
limit. It is shown that the limiting macroscopic evolution has bounded energy
given by the bulk and surface energies of brittle fracture mechanics. The
macroscopic evolution corresponds to the simultaneous evolution
of the fracture surface and linear elastic displacement away from the crack

A new postdoctoral position in continuum mechanics is available at the Weizmann Institute of Science. Candidates should have a strong background in physics and/or theoretical mechanics, as well as experience with analytical and computational methods for solving partial differential equations. Possible projects include the mechanics of frictional sliding, the mechanics of biomaterials, the mechanics of glassy materials and dislocation-mediated plasticity. Highly motivated candidates are requested to send their CV, publications list and statement of research interests to Dr.

In this paper we first obtain the order of stress singularity for a dynamically propagating self-affine fractal crack. We then show that there is always an upper bound to roughness, i.e. a propagating fractal crack reaches a terminal roughness. We then study the phenomenon of reaching a terminal velocity. Assuming that propagation of a fractal crack is discrete, we predict its terminal velocity using an asymptotic energy balance argument. In particular, we show that the limiting crack speed is a material-dependent fraction of the corresponding Rayleigh wave speed.