Supersonic fractures are fractures where the fracture propagation velocity is higher than the

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...

in the material. This phenomenon was first discovered by scientists from the

Max Planck Institute for Metals Research Founded on 18 March 2011, the Max Planck Institute for Intelligent Systems (MPI-IS) is one of the 86 research institutes of the Max Planck Society. With locations in Stuttgart and Tübingen, it combines interdisciplinary research in the growing ...

in Stuttgart (

Markus J. Buehler Markus J. Buehler is an American materials scientist and engineer at the Massachusetts Institute of Technology (MIT), where he holds the endowed McAfee Professorship of Engineering chair. He is a member of the faculty at MIT's Department of Civi ...

and

Huajian Gao Huajian Gao (, born December 7, 1963) is a Chinese-American mechanician who is widely known for his contributions to the field of solid mechanics, particularly on the micro- and nanomechanics of thin films, hierarchically structured materials, ...

) and IBM Almaden Research Center in San Jose, California ( Farid F. Abraham). The issues of intersonic and supersonic fracture become the frontier of dynamic fracture mechanics. The work of Burridge initiated the exploration for intersonic crack growth (when the crack tip velocity V is between the shear in wave speed C^8 and the longitudinal wave speed C^1.Brittle fracture mechanism
Eurekalert.org. Accessed May 19, 2012. Supersonic fracture was a phenomenon totally unexplained by the classical theories of fracture.

Molecular dynamics Molecular dynamics (MD) is a computer simulation method for analyzing the physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamic "evolution" of the ...

simulations by the group around Abraham and Gao have shown the existence of intersonic mode I and supersonic mode II cracks. This motivated a

continuum mechanics Continuum mechanics is a branch of mechanics that deals with the mechanical behavior of materials modeled as a continuous mass rather than as discrete particles. The French mathematician Augustin-Louis Cauchy was the first to formulate such m ...

analysis of supersonic mode III cracks by Yang. Recent progress in the theoretical understanding of

hyperelasticity A hyperelastic or Green elastic materialR.W. Ogden, 1984, ''Non-Linear Elastic Deformations'', , Dover. is a type of constitutive model for ideally elastic material for which the stress–strain relationship derives from a strain energy density ...

in dynamic fracture has shown that supersonic crack propagation can only be understood by introducing a new length scale, called χ; which governs the process of energy transport near a crack tip. The crack dynamics is completely dominated by material properties inside a zone surrounding the crack tip with characteristic size equal to χ. When the material inside this characteristic zone is stiffened due to hyperelastic properties, cracks propagate faster than the longitudinal wave speed. The research group of Gao has used this concept to simulate the Broberg problem of crack propagation inside a stiff strip embedded in a soft elastic matrix. These simulations confirmed the existence of an energy characteristic length. This study also had implications for dynamic crack propagation in composite materials. If the characteristic size of the composite microstructure is larger than the energy characteristic length, χ; models that homogenize the materials into an effective continuum would be in significant error. The challenge arises of designing experiments and interpretative simulations to verify the energy characteristic length. Confirmation of the concept must be sought in the comparison of experiments on supersonic cracks and the predictions of the simulations and analysis. While much excitement rightly centres on the relatively new activity related to intersonic cracking, an old but interesting possibility remains to be incorporated in the modern work: for an interface between elastically dissimilar materials, crack propagation that is subsonic but exceeds the Rayleigh wave speed has been predicted for at least some combinations of the elastic properties of the two materials.

References

Fracture mechanics {{classicalmechanics-stub

See also

References