A methodology to calculate the residual initiation and propagation lives of fatigue cracks in oil... more A methodology to calculate the residual initiation and propagation lives of fatigue cracks in oil pipelines with corrosion-like defects is proposed and applied to predict the residual life of an old duct made of API 5L Gr. B steel, in service for more than 40 years. Since its inauguration, this pipeline has carried several heated products under variable temperatures and pressures. The calculated (nominal) service stresses are very high, due to thermal loads that induce significant bending in curved parts of the duct, with peaks close to the yield strength of the steel. The elastic-plastic fatigue damage at a notch or a corrosion pit root is calculated using the eN method, and the effects of surface semi-elliptical cracks in its internal (or external) wall is studied considering appropriate stress intensity factor expressions and the actual service loads. In the presence of surface flaws associated to stress concentration factors of the order of three, a fatigue crack likely will ini...
Fatigue crack propagation in complex two-dimensional structural components under constant and var... more Fatigue crack propagation in complex two-dimensional structural components under constant and variable amplitude loading is numerically predicted and experimentally verified. Cracks are fatigue propagated under constant and variable amplitude loading in standard CT specimens with holes specially positioned to attract or to deflect the crack. Therefore, the cracks do not follow a straight-line path, but curve toward the hole reaching it or not, depending on the hole positioning. A reliable and cost effective two-phase methodology is used in two pieces of software to numerically predict the fatigue crack propagation. First, the fatigue crack path and its stress intensity factor are calculated in a specialized finite-element software, using small crack increments. Numerical methods are used to calculate the crack propagation path, based on the computation of the crack incremental direction, and the stress-intensity factors KI, from the finite element response. Then, an analytical expre...
A reliable and cost effective two-phase methodology is proposed and implemented in two pieces of ... more A reliable and cost effective two-phase methodology is proposed and implemented in two pieces of software to predict fatigue crack propagation in generic two-dimensional structural components under complex loading. First, the fatigue crack path and its stress intensity factor are calculated in a specialized finite-element software, using small crack increments. At each crack propagation step, the mesh is automatically redefined based on a self-adaptive strategy that takes into account the estimation of the previous step stress analysis numerical errors. Numerical methods are used to calculate the crack propagation path, based on the computation of the crack incremental direction, and the stress-intensity factors KI, from the finite element response. An application example presents a comparison between numerical simulation results and those measured in physical experiments. Then, an analytical expression is adjusted to the calculated KI(a) values, where a is the length along the crac...
A methodology to calculate the residual initiation and propagation lives of fatigue cracks in oil... more A methodology to calculate the residual initiation and propagation lives of fatigue cracks in oil pipelines with corrosion-like defects is proposed and applied to predict the residual life of an old duct made of API 5L Gr. B steel, in service for more than 40 years. Since its inauguration, this pipeline has carried several heated products under variable temperatures and pressures. The calculated (nominal) service stresses are very high, due to thermal loads that induce significant bending in curved parts of the duct, with peaks close to the yield strength of the steel. The elastic-plastic fatigue damage at a notch or a corrosion pit root is calculated using the eN method, and the effects of surface semi-elliptical cracks in its internal (or external) wall is studied considering appropriate stress intensity factor expressions and the actual service loads. In the presence of surface flaws associated to stress concentration factors of the order of three, a fatigue crack likely will ini...
Fatigue crack propagation in complex two-dimensional structural components under constant and var... more Fatigue crack propagation in complex two-dimensional structural components under constant and variable amplitude loading is numerically predicted and experimentally verified. Cracks are fatigue propagated under constant and variable amplitude loading in standard CT specimens with holes specially positioned to attract or to deflect the crack. Therefore, the cracks do not follow a straight-line path, but curve toward the hole reaching it or not, depending on the hole positioning. A reliable and cost effective two-phase methodology is used in two pieces of software to numerically predict the fatigue crack propagation. First, the fatigue crack path and its stress intensity factor are calculated in a specialized finite-element software, using small crack increments. Numerical methods are used to calculate the crack propagation path, based on the computation of the crack incremental direction, and the stress-intensity factors KI, from the finite element response. Then, an analytical expre...
A reliable and cost effective two-phase methodology is proposed and implemented in two pieces of ... more A reliable and cost effective two-phase methodology is proposed and implemented in two pieces of software to predict fatigue crack propagation in generic two-dimensional structural components under complex loading. First, the fatigue crack path and its stress intensity factor are calculated in a specialized finite-element software, using small crack increments. At each crack propagation step, the mesh is automatically redefined based on a self-adaptive strategy that takes into account the estimation of the previous step stress analysis numerical errors. Numerical methods are used to calculate the crack propagation path, based on the computation of the crack incremental direction, and the stress-intensity factors KI, from the finite element response. An application example presents a comparison between numerical simulation results and those measured in physical experiments. Then, an analytical expression is adjusted to the calculated KI(a) values, where a is the length along the crac...
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