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3D CAFE modelling of ductile fracture in gas pipeline steel

Soberanis, Sabino Ayvar (2007) 3D CAFE modelling of ductile fracture in gas pipeline steel. PhD thesis, University of Sheffield.

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This thesis describes a series of experimental and computational studies carried out on Xl00 pipeline steel with the objective to characterise the tearing resistance of the material. A Cellular Automata - Finite Element(CAFE) technique was used in this work to develop a 3D numerical model to provide a more realistic description of the ductile damage mechanisms of the pipeline steel. In this model, the Rousselier micro-mechanisms damage theory and an appropriate cell size in a CA array represent the material behaviour. The experimental work consisted of laboratory tensile specimens in four different orientations of the material to determine the properties of the pipeline steel. Two novel designs were conducted to measure the deformation behaviour when loaded in the through wall direction. Compact C(I) and tear specimens were also tested to capture the crack growth, and the flat and shear fracture characteristics. The experimental data of laboratory samples were used to calibrate the continuum damage models. SEM (Scanning Electron Microscope) micrograph observations were carried out in tensile tests, standard C(f), slant notch C(f) and tear specimens. These observations revealed that spacing between large dimples of flat fracture are of the order of five times larger than shear fracture. It is important since the transfer of the material model parameters is made by modifying the cell size according to the average spacing between large voids in the material, d. Therefore 3D CAFE models for flat and shear fracture were created according to the microstructural characteristics to interpret the experimental findings. The main aim of the research reported here is to investigate transferability of the damage model parameters to gas pipelines steels from laboratory scale samples, and then to predict the fracture response of real structures. The CAFE technique has been shown to be a powerful tool in reducing simulation time whilst maintaining good predictions of shear damage and material resistance in terms of CTOA criterion. This was not achieved by classical FE methods where a very fine mesh is required to represent the characteristic dimension of ductile fracture. Similar reasonable results were obtained when anisotropic flat fracture was predicted but transferability of the damage parameters to CT specimens needs still further investigation.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Mechanical Engineering (Sheffield)
Other academic unit: Department of Mechanical Engineering
Identification Number/EthosID: uk.bl.ethos.486776
Depositing User: EThOS Import Sheffield
Date Deposited: 03 Mar 2016 11:55
Last Modified: 03 Mar 2016 11:55
URI: http://etheses.whiterose.ac.uk/id/eprint/10310

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