Ares J. Rosakis Ares J. Rosakis
Theodore von Kármán Professor of Aeronautics and Mechanical Engineering

Research Interests

Dynamic Shear-Dominated Intersonic Crack Growth in Homogeneous Systems with Weak Crack Paths of Various Geometries
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Collaborator: Student: G. Lykotrafitis, Caltech

Dynamic, shear dominated cracks propagating in the interfaces between materials characterized by a high mismatch in wave speeds (e.g. metal/polymer) are studied using optical techniques (CGS and Photoelasticity) and high-speed photography. These cracks accelerate, within microseconds, to the shear wave speed, (c ~ 1000 m/s), of the more compliant of the two solids (solid -1). At this speed they propagate in a stable manner until enough excess energy is supplied to the system. Subsequently, they further accelerate to supersonic speeds, (v > c ~ 2000 m/s), with respect to the polymer side, eventually reaching the Rayleigh wave speed of the metal, c ~ 3100 m/s. Such cracks become almost completely shear dominated and exhibit large scale frictional contact between the crack faces. They also feature the distinct (shear) shock wave structure expected of intersonically or supersonically moving disturbances. Intersonic crack growth along the fibers of unidirectional graphite/epoxy composite plates is also investigated. Here also, shock waves are visible and the crack speed is as high as 6,000 m/s. Finally, intersonic shear cracks propagating along the interface between two identical homogeneous and isotropic solids bonded by means of bonds of various strengths are also studied. This is the first time that intersonic and supersonic crack growth has ever been reported in a laboratory setting. However, in a much larger scale, such processes are known by geophysicists to occur in stratified layers within the earth's crust (shallow crustal earthquakes). The similarities between the laboratory observations and crustal earthquakes are a subject of intense interest and are systematically pursued.

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