Crack Front Waves in Dynamic Fracture

J. FINEBERG, E. SHARON and G. COHEN

Received 3 June 2002; accepted in revised form 23 March 2003

Abstract. A rapidly moving tensile crack is often idealized as a one-dimensional object moving through an ideal

two-dimensional material, where the crack tip is a singular point.When a material is translationally invariant in the

direction normal to the crack’s propagation direction, this idealization is justified. A real tensile crack, however,

is a planar object whose leading edge forms a propagating one-dimensional singular front (a ‘crack front’). We

consider the interaction of a crack front with localized material inhomogeneities (asperities), in otherwise ideal

brittle amorphous materials. We review experiments in these materials which indicate that this interaction excites

a new type of elastic wave, a front wave, which propagates along the crack front. We will show that front waves

(FW) are highly localized nonlinear entities that propagate along the front at approximately the Rayleigh wave

speed, relative to the material. We will first review some of their characteristics. We then show that by breaking

the translational invariance of the material, FWeffectively act as a mechanism by which initially ‘massless’ cracks

acquire inertia.

Key words: Brittle fracture, crack front waves, localized waves, solitary waves.