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The near-tip field at high crack velocities

  • K. B. Broberg

Abstract

Several velocity regions, distinctly different as regards crack edge propagation characteristics, can be distinguished. The simplest case is mode III with only the subsonic and the supersonic regions. For modes I and II four different regions can be recognized. When analyzing the near-tip field at leading and trailing edges it is found that some velocity regions are forbidden. The most important field characteristic is the energy flow to or from the edge. A clear difference exists between modes I and II: for mode I the whole region between Rayleigh and irrotational wave velocities is forbidden, for mode II only the subsonic super-Rayleigh region.

In attempts to provoke crack edge propagation at a velocity in a forbidden region, the result appears to be edge propagation at velocities alternating between velocities in non-forbidden regions, above and below the attempted velocity. A study of the stresses ahead of the edge region of a mode II crack expanding in both directions indicates that the edge might accelerate (by a jump) spontaneously from a sub-Rayleigh to an intersonic velocity.

A study of the stresses ahead of the edge region of a mode II crack expanding in both directions indicates that the edge might accelerate (by a jump) spontaneously from a sub-Rayleigh to an intersonic velocity.

Keywords

Energy Flow Crack Edge Mass Velocity Displacement Gradient Supersonic Region 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Résumé

Selon les caractéristiques de propagation du bord d’une fissure, on peut distinguer divers registres distincts de vitesses de fissuration. Le cas le plus simple est celui du Mode III, où Ton ne rencontre que les vitesses subsoniques et supersoniques. Les Modes I et II conduisent a distinguer quatre vitesses differentes. Lorsqu’on analyse le champ du voisinage de l’extrémité de la fissure en ses bords moteurs, on trouve que certaines vitesses sont proscrites. La caractéristique la plus importante du champ est le transfert d’énergie depuis ou vers le bord. II existe une distinction claire entre les Modes I et II: en Mode I, toute la gamme comprise entre les vitesses des ondes de Rayleigh et d’une onde irrotationnelle sont prescrites; en Mode II, seule est proscrite la gamme subsonique supérieure à l’onde de Rayleigh.

Lorsqu’on tente de provoquer une propagation des bords d’une fissure à une vitesse dans une gamme proscrite, le resultat semble etre une propagation de bord à des vitesses oscillant entre deux gammes non proscrites, de part et d’autre de la vitesse visée.

En étudiant les contraintes en avant du bord d’une fissure de Mode II se developpant selon les deux directions imposees, on constate que le bord peut spontanement s’accélérer suivant un ressaut, en passant d’une vitesse inferieure a une onde de Rayleigh a une une vitesse transonique.

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Copyright information

© Kluwer Academic Publishers, Dordrecht 1989

Authors and Affiliations

  • K. B. Broberg
    • 1
  1. 1.Department of Solid MechanicsLund Institute of TechnologyLundSweden

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