School of Mechanical Engineering Prof. Dov Sherman

School of Mechanical Engineering Seminar
Monday, March 12, 2018 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

When crack meets defects-

Atomistic scale Jog like surface instability

Dov Sherman

School of Mechanical Engineering

Tel-Aviv University, Tel-Aviv 69978, Israel

This talk is the second in a series of talks about fracture in the atomistic scale. In the first talk we discussed the interaction between the external driving force and bond breaking mechanisms along the curved crack front. In this talk we will describe and model the interaction between dynamic crack and point (atomistic) defects, and the generated surface instabilities.

Recently, we generalized the interaction in brittle cubic crystals by cleaving silicon and germanium doped with boron, oxygen, phosphorous, and gallium. At certain crack speed and chemical local strain energy induced by the dopant, the crack will deflect to generate an atomistic height wedge like jog (like in dislocations) to diminish the local chemical strain energy. Jogs are pile-up up to initiate a micron scale ridge.

A theoretical model was developed, based on continuum energy minimization law (even in this scale), where the crack speed and the local chemical strain energy play a major role. The model predicts the maximal crack speed at deflection.  The major outcome of the model is that even the densest jogs have only limited influence on crack speed.