Velocity correlated crack front and surface marks in single crystalline silicon

Lv Zhao,Didier Bardel,Daniel Nelias,Anne Maynadier

doi:10.1038/s41467-018-03642-w

Abstract

Single crystalline silicon fractures on low-energy cleavage planes such as (111) and (110). The crack propagation cannot accurately be predicted by linear elastic fracture mechanics since it does not account for small scale and inelastic phenomena such as atomic lattice trapping. Here we show that, under pure bending load, (110) cleavage in silicon single crystal rapidly accelerates to 3700 m/s without crack path deviation or crack branching, contrasting previous observations. We highlight that the crack front shape involves strong velocity dependence and presents a curvature jump during very high-speed crack growth. In addition, we observe special marks—a kind of periodic surface undulation—that exclusively arise on the rapid fracture surfaces, and we suggest that they are front wave traces resulting from an intrinsic local velocity fluctuation. This finding gives insight to the wavy nature of the crack front in the absence of material asperity.

Highlights

Single crystalline silicon fractures on low-energy cleavage planes such as (111) and (110)
Thanks to meticulous fractographic analysis, it is for the first time highlighted that the crack front shape is strongly dependent on the crack velocity and involves a curvature jump when propagating faster than 2800 m/s
With the curvature jump, special surface marks (SSMs) have been observed on the fracture surface. These marks are periodic undulations and involve significantly different features from the Wallner lines, and we propose that they are front wave (FW) traces resulting from a fracture toughness induced local velocity fluctuation

Summary

Introduction

Single crystalline silicon fractures on low-energy cleavage planes such as (111) and (110). Another kind of large plane deflection—from (110) [110] to (111)—has been observed under 3-line bending condition11, 16 This deflection involved velocity dependence and occurred when the crack propagated faster than 1700 m/s. We show that (110) [110] cleavage neither involves cleavage plane deflection nor crack branching, even in an extremely high-speed fracture process (3700 m/s) This finding is contradictory with the aforementioned observations in 3-line bending tests. With the curvature jump, special surface marks (SSMs) have been observed on the fracture surface These marks are periodic undulations and involve significantly different features from the Wallner lines ( present), and we propose that they are FW traces resulting from a fracture toughness induced local velocity fluctuation

Methods

Results

Conclusion