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XXI ICTAM, 1521 August 2004, Warsaw, Poland BRANCHING INSTABILITY OF BRITTLE FRACTURE
 

Summary: XXI ICTAM, 15­21 August 2004, Warsaw, Poland
BRANCHING INSTABILITY OF BRITTLE FRACTURE
M. Adda­Bedia
Laboratoire de Physique Statistique, Ecole Normale Supérieure
24 rue Lhomond, 75231 Paris Cedex 05, France
Summary A new method for determining the elastodynamic stress fields associated with the propagation of antiplane branched cracks
is presented. The exact dependence of the stress intensity factor just after branching is given as a function of the stress intensity factor
just before branching, the branching angle and the instantaneous velocity of the crack tip. The jump in the dynamic energy release rate
due to the branching process is also computed. Applying a growth criterion for a branched crack, it is shown that the minimum speed
of the initial single crack which allows branching is equal to 0.39c, where c is the shear wave speed. At the branching threshold, the
corresponding bifurcated cracks start their propagation at a vanishing speed with a branching angle of approximately 40 degrees. Using
these exact results, the branching of a single propagating crack under mode I loading is also considered and the critical velocity for
branching is computed.
INTRODUCTION
An issue of great interest in crack dynamics is the question of understanding the instabilities associated with the appear-
ance and evolution of kinked or bifurcated cracks. We are particularly interested in this phenomenon in brittle materials,
in which several experiments [1, 2, 3] have shown evidence of these instabilities. A main experimental distinction can
be made between micro­branches and macro­branches. The fact is that over a crack velocity threshold, the so called
micro­branching instability sets in : the broken surface left by the crack shows a dense array of micro­kinks that were
incipient cracks that aborted quickly their inroad into the material. The angle that these micro­cracks make with the main

  

Source: Adda-Bedia, Mokhtar - Laboratoire de Physique Statistique, Département de Physique, École Normale Supérieure

 

Collections: Physics