Single crack propagation

Pre-cracked specimens are sometimes useful for other reasons than the analysis that they afiford in relation to stress-intensity factors. Such applications may be associated with the simulation of service situations, the relative ease with which stress-corrosion cracks can be initiated at pre-cracks or the advantages that sometimes accrue from the propagation of a single crack. The claim that has sometimes been made of pre-cracked specimen tests-that they circumvent the initiation stage of cracking in plain specimens, erroneously assumed invariably to be related to the creation of a corrosion pit that provides a measure of stress concentration approaching that... 

Based on a model for crack propagation in a single crack-tip craze [50], verified by more detailed treatments [51, 52, 53], it is shown that under conditions of SSY, where the crack propagation is determined by the far field stress intensity K ... 

Aveston, J., Cooper, G.A., Kelly, A. (1971), Single and multiple fracture , in The Properties of Fiber Composites, IPC Science Technology Press, Guildford, UK, 15-22 Bahr, H.A., Weiss, H.J., Maschke, H.G., Meissner, F. (1988), Multiple crack propagation in strip caused by thermal shock , Theor. Appl. Fract. Mech., 10, 219-226. Bannister, M.K., Swain, M.V. (1990), Thermal shock of a titanium diboride based composite , Ceram. Int., 16, 77-83... 

Figure 17 Fracture mechanics data plotted as log apparent crack velocity vs. stress intensity. Each point represents the exposure of a single specimen. The specimens were immersed in a simulated impregnation zone liquor at 115°C for 151 days. No crack propagation was observed at anodic protection potentials (—730 mVSCE). (From Ref. 10.)...

A brittle behavior. The force-displacement (F-d) curves are linear elastic. The crack propagates in an unstable way. The damage mechanisms have not been initiated before failure. The fracture surfaces are very smooth and mirror-like. At the microscopic scale, they are believed to be associated with the development of a single crack. 

From the present results, and as long as the crack propagates by a single craze, the calculations indicate that thermal blunting alone cannot be invoked as the explanation of the brittle-to-ductile transition observed at high load-... 

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