Breakdown of Linear Elastic Fracture Mechanics near the Tip of a Rapid Crack

 

Ariel Livne, Eran Bouchbinder, and Jay Fineberg

Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel

(Received 30 July 2008; published 30 December 2008)

 

We present high resolution measurements of the displacement and strain fields near the tip of a dynamic

(mode I) crack. The experiments are performed on polyacrylamide gels, brittle elastomers whose fracture

dynamics mirror those of typical brittle amorphous materials. Over a wide range of propagation velocities

(0:20:8cs), we compare linear elastic fracture mechanics (LEFM) to the measured near-tip fields.We find

that, sufficiently near the tip, the measured stress intensity factor appears to be nonunique, the crack tip

significantly deviates from its predicted parabolic form, and the strains ahead of the tip are more singular

than the r1=2 divergence predicted by LEFM. These results show how LEFM breaks down as the crack

tip is approached.