This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: We have all seen something suddenly break: a phone screen cracks, a plastic object snaps or a piece of glass shatters. To our eyes, the failure seems to happen all at once.
But what if the most important part of the break happens long before the final snap? A new study presents a physical picture of how materials fail. The researchers found that cracks can begin as tiny, two-dimensional patches that grow extraordinarily slowly, at speeds ranging from microns to millimeters per second.
Only after these patches grow to span the thickness of the material do they transform into the rapidly moving cracks associated with sudden, explosive fracture. The research, published in the journal Physical Review Letters, was conducted by Yuval Paz and Jay Fineberg of the Racah Institute of Physics at The Hebrew University of Jerusalem, together with Meng Wang of the Beijing Institute of Technology and Mokhtar Adda-Bedia of CNRS, ENS de Lyon and Université de Lyon. For decades, scientists have used linear elastic fracture mechanics, or LEFM, to understand why materials break.
Classical fracture theory says that a crack smaller than a certain critical size, known as the Griffith length, remains stable. Once it grows beyond that size, it becomes unstable and rapidly accelerates, eventually reaching speeds approaching the characteristic speed of sound in the material. The theory is remarkably successful at describing cracks once they are racing through a material.
But it leaves a fundamental question unanswered: How does the crack get started? The team set out to investigate this missing beginning of the fracture story. Their experiments revealed that, in three-dimensional materials, fracture can begin when the material reaches a critical stress.
A tiny broken region nucleates, not as the familiar line-shaped crack, but as a two-dimensional patch. That patch expands extremely slowly in a process known as creep. Using a specially designed experimental system and high-speed imaging, the researchers followed these fractured regions from their first appearance through slow creep and, finally, rapid rupture.
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