The Dynamics of Fast Fracture

By Eran Sharon and Jay Fineberg

 

What determines the strength of the materials around us?

We know that the chemical bonds connecting the molecules

that compose a given material hold it together, but to what

degree do the bond strengths themselves determine the

strength of a given structure? In order for a structure to

separate, one must at least supply enough energy to break the

bonds along a plane that cuts through it. The cumulative energy

of these bonds provides an energy barrier that ensures the

structure's mechanical stability. The existence of a crack in an

otherwise perfect solid is Nature's way to efficiently supply the

energy to overcome this barrier. In a material under stress, a

nearly singular stress field occurs at the tip of a crack. This large

stress concentration at the tip of a crack serves as an energy

¬funnel║ that can enable a crack to propagate by efficiently

severing bonds in only the immediate vicinity of its tip. Thus,

the ultimate strength of any material is governed by the

existence of the cracks within it.