The fracture and fatigue properties of cast irons used for trunk mains in the water industry
In order to assess the remaining life of cast iron assets in the water sector, an understanding of their fracture and fatigue characteristics is necessary. The present work is concerned with the toughness and Paris crack growth behaviour of cast iron materials with a range of micro-structures, taken from trunk mains currently in service. When considered with other data from the literature, the results from the present study enable the range of fatigue crack growth behaviour likely to be seen in service to be quantified. The role of microstructure in fracture and fatigue behaviour is discussed. Calculations of fatigue life based on integration of the Paris law are then carried out and compared with previously published data for samples from cast iron distribution mains. The results from these investigations support the development of asset management tools for use in the water industry.
Some observations on the strength and fatigue properties of samples extracted from cast iron water mains
The strength and fatigue properties of cast iron samples taken from water distribution mains have been investigated. Specimens were sourced from three sections of pipe which had experienced varying amounts of corrosion in service, enabling the variable of pipe condition to be incorporated within the study. The strengths in four-point flexure of small specimens from the pipes examined were described using Weibull statistics; different characteristic strengths and Weibull moduli were obtained, according to the pipe condition. A further set of samples from each pipe were subjected to flexural fatigue at a range of stress levels (different stress levels were chosen for each pipe based on the short-term strength properties) and residual strength tests were carried out on the surviving samples from one stress level for each pipe. There is evidence of a fatigue effect for all sample sets. There were slight differences in the residual strength behaviour - the residual strength of the survivors was reduced in the samples from the section in best condition while the residual strength of the survivors from the other two pipe sections was relatively unaffected. These trends are discussed with reference to condition and fatigue stress level. The results suggest that mechanical fatigue may be a factor in the failure of water distribution pipes. The results may have implications for large diameter trunk mains as well as the small diameter water distribution pipes tested here. To assess the effect in more detail, consideration needs to be given to scaling effects in fatigue and the likely levels of any fatigue stress seen in service.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.