An analytical method is being developed to determine the signature of an acoustic emission waveform from a growing crack and the results of this analysis are compared to experimentally obtained values. Within the assumptions of linear elastic fracture mechanics, a two dimensional model is developed to examine a semi-infinite crack that, after propagating with a constant velocity, suddenly stops...

The propagation of fractures during the drying of a colloidal silica suspension confined in a vertical microtube is investigated. During the drying process, the particle concentration increases until gel formation. In the gelled region, the tensile stresses increase and lead to the formation of two vertical perpendicular cracks propagating in the drying direction, dividing the tube into four eq...

We present an experimental study of the motion of a viscoelastic micellar fluid around a moving cylinder, which ranges from fluidlike flow to solidlike tearing and fracture, depending on the cylinder radius and velocity. The observation of crack propagation driven by the cylinder indicates an extremely low tear strength, approximately equal to the steady state surface tension of the fluid. At t...

We study an evolution model for fractured elastic materials in the 2-dimen-sional case, for which the crack path is not assumed to be known a priori. We introduce some general assumptions on the structure of the fracture sets suitable to remove the restrictions on the regularity of the crack sets and to allow for kinking and branching to develop. In addition we define the front of the fracture ...

This paper first examines the problems of using impact methods to achieve fast fracture of polymers. On-specimen gauges are employed to obtain the distribution of transient and other stresses in different parts of the specimen. A new method is then introduced that avoids transient forces and achieves crack velocities in small specimens of tough polymers of over 300 m s-l. It provides for the me...

We investigate the dynamic fracture of a close-packed monolayer of particles, or particle raft, floating at a liquid-gas interface induced by the localized addition of surfactant. Unusually for a two-dimensional solid, our experiments show that the speed of crack propagation here is not affected by the elastic properties of the raft. Instead it is controlled by the rate at which surfactant is a...

We study a theoretical model of mud cracks, that is, the fracture patterns resulting from the contraction with drying in a thin layer of a mixture of granules and water. In this model, we consider the slip on the bottom of this layer and the relaxation of the elastic field that represents deformation of the layer. Analysis of the one-dimensional model gives results for the crack size that are c...

The role of particle-toughening for increasing impact damage resistance in carbon fibre reinforced polymer (CFRP) composites was investigated. Five carbon fibre reinforced systems consisting of four particle-toughened matrices and one system containing no toughening particles were subjected to low velocity impacts ranging from 25 J to 50 J to establish the impact damage resistance of each mater...

Associate Professor, Graduate Aeronautical laboratories, California Institute of Technology, Pasadena, Calif. The tip velocity of a crack propagating through a vi scoelastic material depends on geometry, apptied toad and its history , and material properties. A consideration of the work done by the unloading tractions at the crack tip shows that, f or a large crack propagating throitgh an infin...

In 2004, a team comprised of researchers and service providers launched the Safer Crack Use, Outreach, Research and Education (SCORE) project in the Downtown Eastside of Vancouver, British Columbia, Canada. The project was aimed at developing a better understanding of the harms associated with crack cocaine smoking and determining the feasibility of introducing specific harm reduction strategie...