Measurements of crack velocities in KC1 crystals an order of magnitude greater than the velocity of the fastest elastic wave are reported. Fracture was produced by irradiation with a giant impulse laser, and average crack propagation velocities of the order of 10 ~ to 105 m/sec were inferred from the sizes of cleavage cracks in photographs taken approximately 80 nsec after beginning of irradiation.These results are the first experimental observations which contradict the prediction of crack-propagation theories that crack velocities cannot exceed sound speeds. The supersonic speeds are attributed to the unusual experimental conditions, which permitted energy to be supplied to the crack front at unusually high rates. A plasma, induced within the specimen by the laser pulse, is shown to be capable of driving a crack at supersonic speeds.

No abstract

No abstract

A new inlet design for a scramjet engine has been designed at The University of Queensland, to be used as part of a propulsion system to launch small payloads into orbit.It is known as the CREST inlet, and was designed using similar streamtracing techniques used in the development of the REST inlet. The performance of the CREST inlet is undetermined. As this engine is designed to accelerate a vehicle from Mach 5 to Mach 10, it is important throughout the trajectory that the inlet provides suitable conditions to the combustor.One of the two major aims of this thesis is to provide a preliminary analysis of the inlet, using quasi one dimensional methods, to determine the general performance and highlight areas that may hamper performance. At the lower range of Mach numbers for which this engine must operate, dual mode combustion will be present, where both subsonic and supersonic flow occur in the combustor. This is difficult to sustain, and therefore the other main aim of the thesis is to determine the possibility of using an expansion ramp combustor to hold the dual mode combustion. A quasi one dimensional code was used to determine the performance over the trajectory. For the expansion ramp combustor preliminary investigation, the numerical simulation code Eilmer3 was used.Several sonic injection cases and a porous injection case were simulated.The one dimensional analysis demonstrated satisfactory performance of the inlet over the trajectory. It showed a method of providing heat is required for initial ignition at low Mach numbers, and for low angles of attack further compression is necessary. A significant portion of the flight can be in the dual mode combustion region, indicating it is necessary to provide a method to sustain this. The two dimensional analysis showed that the expansion ramp combustor is a viable option to sustain dual mode combustion.Several factors appear to affect the expansion ramp's ability to generate the recirculation zone and separation indicative of dual mode combustion. These were injection angle and location of the ramp; the boundary layer size being a large contributing factor.From this thesis, the CREST inlet is shown to be a promising candidate for the accelerator scramjet engine, providing good performance with a preliminary, nonoptimised combustor design. The issues identified in this thesis, including the low initial ii temperature, can be resolved by further work. Initially, the expansion ramp combustor appears to be a viable method of sustaining dual mode combustion, and further analysis of it may provide a unique solution to this problem.iii AcknowledgementsCompleting this thesis could not have been done without the support of several people.Chief among these is Dr Vincent Wheatley, who has been the major source of ideas, inspiration and advice, guiding the thesis; so I would like to extend a warm thank you to him. Thank you also to Professor Michael Smart for support (and use of dm_cycle).My parents, Stephen and Meryl Curran, are always more than happy to lend a re...

No abstract