2010
|
Nonn, A.; Erdelen-Peppler, M.; Kalwa, C. Numerical and experimental investigation of the influence of HAZ on the fracture behavior of longitudinal welded linepipes Werkstoffsimulation Proceedings Article In: Fracture of Materials and Structures from Micro to Macro Scale, 18th European Conference on Fracture, Dresden, Germany, 2010. @inproceedings{,
title = {Numerical and experimental investigation of the influence of HAZ on the fracture behavior of longitudinal welded linepipes},
author = {A. Nonn and M. Erdelen-Peppler and C. Kalwa},
year = {2010},
date = {2010-08-30},
booktitle = {Fracture of Materials and Structures from Micro to Macro Scale, 18th European Conference on Fracture},
address = {Dresden, Germany},
abstract = {The present paper deals with the influence of heat affected zone (henceforth HAZon the fracture performance of longitudinal welded linepipes in dependence on constraint level. It has been shown that toughness values of HAZ obtained from standard fracture mechanics tests lead to uneconomic linepipe design for two reasons. The first reason is that laboratory specimens with higher constraint level generally exhibit lower fracture resistance compared to flawed linepipes. The second one has to do with a higher probability of cleavage failure occurrence in the laboratory specimen than in the linepipes due to larger areas of lower toughness (so called local brittle zones (LBZintersected by crack front. In recent years numerous studies have been initiated with the objective to quantify the constraint level and thus to allow for less conservative linepipe safety assessment by applying constraint corrected toughness values. However, the main focus of these studies has hitherto been on the homogeneous materials, failing to account for the possible effects of different microstructures within the heterogeneous HAZ. This paper seeks to close this gap by reporting on results from tests on fracture mechanics specimens of a high strength X80 steel, i.e. SENB and SENT specimens as well as results from ring expansion tests. Both, deep and shallow cracks are inserted in the fracture mechanics specimens and rings targeting the fusion line (FL. By varying the initial crack size and sample type, different constraint levels are achieved and subsequently quantified using numerical methods. Besides constraint observations, post metallographic analyses are performed to identify exact HAZ microstructure involved at the crack tip. Finally, the influence of HAZ properties, flaw size and geometry on the failure behaviour of the linepipes has been demonstrated and assessed. Based on the combination of the results from constraint studies and the post metallographic analyses, the methodology is proposed which enables simple quantitative prediction of toughness values for safe and economic design of linepipes with flaws located in HAZ.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The present paper deals with the influence of heat affected zone (henceforth HAZon the fracture performance of longitudinal welded linepipes in dependence on constraint level. It has been shown that toughness values of HAZ obtained from standard fracture mechanics tests lead to uneconomic linepipe design for two reasons. The first reason is that laboratory specimens with higher constraint level generally exhibit lower fracture resistance compared to flawed linepipes. The second one has to do with a higher probability of cleavage failure occurrence in the laboratory specimen than in the linepipes due to larger areas of lower toughness (so called local brittle zones (LBZintersected by crack front. In recent years numerous studies have been initiated with the objective to quantify the constraint level and thus to allow for less conservative linepipe safety assessment by applying constraint corrected toughness values. However, the main focus of these studies has hitherto been on the homogeneous materials, failing to account for the possible effects of different microstructures within the heterogeneous HAZ. This paper seeks to close this gap by reporting on results from tests on fracture mechanics specimens of a high strength X80 steel, i.e. SENB and SENT specimens as well as results from ring expansion tests. Both, deep and shallow cracks are inserted in the fracture mechanics specimens and rings targeting the fusion line (FL. By varying the initial crack size and sample type, different constraint levels are achieved and subsequently quantified using numerical methods. Besides constraint observations, post metallographic analyses are performed to identify exact HAZ microstructure involved at the crack tip. Finally, the influence of HAZ properties, flaw size and geometry on the failure behaviour of the linepipes has been demonstrated and assessed. Based on the combination of the results from constraint studies and the post metallographic analyses, the methodology is proposed which enables simple quantitative prediction of toughness values for safe and economic design of linepipes with flaws located in HAZ. |
Nonn, A.; Kalwa, C. Modeling of damage behavior of high strength pipeline steel Werkstoffsimulation Proceedings Article In: Fracture of Materials and Structures from Micro to Macro Scale, 18th European Conference on Fracture, Dresden, Germany, 2010. @inproceedings{,
title = {Modeling of damage behavior of high strength pipeline steel},
author = {A. Nonn and C. Kalwa},
year = {2010},
date = {2010-08-30},
booktitle = {Fracture of Materials and Structures from Micro to Macro Scale, 18th European Conference on Fracture},
address = {Dresden, Germany},
abstract = {The worldwide growing importance of oil and gas transport has led to increasing application of high strength steels, e.g. X100, for pipelines. Although the development of the new high-strength steel grades has been recently intensified, detailed comprehension of fracture performance of high strength linepipe is still missing. Hence, outdated methods are used for the design against fracture resulting in insufficient utilization of material reserves. This paper aims to provide overall characterization of mechanical properties of X100 pipeline steel and to allow for more precise estimation of failure process by taking the microstructure into account. By conducting metallographic analyses, the microstructure of X100 has been characterized with objective to identify variables, e.g. size and distribution of voids, inclusions and precipitations relevant for damage process. Subsequently, these variables have been linked to damage parameters of the micromechanics-based Gurson-Tvergaard-Needleman (henceforth GTN) model. This model adequately describes ductile failure for arbitrary crack and component geometry by incorporating the influence of local damage on the yielding behavior. However, it requires besides microstructural variables a quantification of additional parameters by performing tests on the round bar specimens with different notch geometry. The results from fracture mechanics tests on deep-notched SENB and SENT specimens serve the validation of GTN model with respect to accurate prediction of global load-deformation and crack resistance behavior. The transferability of the model parameters was demonstrated by means of results from tests on the shallow-notched specimens and ring expansion tests. Additionally, the effect of microstructure modification on fracture behavior of flawed linepipes was studied and evaluated by varying microstructure-related parameters, e.g. initial porosity f 0 and volume fraction of newly-nucleating voids f N . Based on the results obtained from damage modeling and parameter studies, recommendations have been derived for the modifications of X100 microstructure for purposes to improve toughness properties.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The worldwide growing importance of oil and gas transport has led to increasing application of high strength steels, e.g. X100, for pipelines. Although the development of the new high-strength steel grades has been recently intensified, detailed comprehension of fracture performance of high strength linepipe is still missing. Hence, outdated methods are used for the design against fracture resulting in insufficient utilization of material reserves. This paper aims to provide overall characterization of mechanical properties of X100 pipeline steel and to allow for more precise estimation of failure process by taking the microstructure into account. By conducting metallographic analyses, the microstructure of X100 has been characterized with objective to identify variables, e.g. size and distribution of voids, inclusions and precipitations relevant for damage process. Subsequently, these variables have been linked to damage parameters of the micromechanics-based Gurson-Tvergaard-Needleman (henceforth GTN) model. This model adequately describes ductile failure for arbitrary crack and component geometry by incorporating the influence of local damage on the yielding behavior. However, it requires besides microstructural variables a quantification of additional parameters by performing tests on the round bar specimens with different notch geometry. The results from fracture mechanics tests on deep-notched SENB and SENT specimens serve the validation of GTN model with respect to accurate prediction of global load-deformation and crack resistance behavior. The transferability of the model parameters was demonstrated by means of results from tests on the shallow-notched specimens and ring expansion tests. Additionally, the effect of microstructure modification on fracture behavior of flawed linepipes was studied and evaluated by varying microstructure-related parameters, e.g. initial porosity f 0 and volume fraction of newly-nucleating voids f N . Based on the results obtained from damage modeling and parameter studies, recommendations have been derived for the modifications of X100 microstructure for purposes to improve toughness properties. |
2009
|
Bleck, W.; Dahl, W.; Nonn, A.; Amlung, L.; Feldmann, M.; Schäfer, D.; Eichler, B. Numerical and experimental analyses of damage behaviour of steel moment connection Werkstoffsimulation Artikel In: Engineering Fracture Mechanics, Bd. 76, Nr. 10, S. 1531 - 1547, 2009, ISSN: 0013-7944, (MatModels 2007). @article{BLECK20091531,
title = {Numerical and experimental analyses of damage behaviour of steel moment connection},
author = {W. Bleck and W. Dahl and A. Nonn and L. Amlung and M. Feldmann and D. Schäfer and B. Eichler},
url = {http://www.sciencedirect.com/science/article/pii/S001379440900085X},
doi = {https://doi.org/10.1016/j.engfracmech.2009.03.004},
issn = {0013-7944},
year = {2009},
date = {2009-01-01},
journal = {Engineering Fracture Mechanics},
volume = {76},
number = {10},
pages = {1531 - 1547},
abstract = {Plastic design allows the exploitation of the full resistance of steel structures by taking advantage of stress–redistributions due to plastic strains exceeding the yield strain. Especially in seismic design the utilization of material reserves and the formation of plastic hinges play an important role. In devastating earthquakes in Northridge (USA) and Kobe (Japan) brittle fracture of welded connections in steel moment frames occurred prior to formation of plastic hinges and utilization of plastic material reserves. The subsequent research works resulted in improved design rules and recommendations for these kinds of failure. But to guarantee sufficient ductile performance of these connections also in the upper shelf region, plastic and earthquake resistant design rules should take into account degradation of strain capacity and toughness properties due to quasi static and especially seismic loading. In the scope of the current European project “Plastotough”, the main objective is to derive quantified toughness design rules in the upper shelf based on the strain requirements opposed to strain capacities. This paper gives an overview over the research work in performance and shows recent results from experimental and numerical analyses performed within this project for monotonic and cyclic loading.},
note = {MatModels 2007},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Plastic design allows the exploitation of the full resistance of steel structures by taking advantage of stress–redistributions due to plastic strains exceeding the yield strain. Especially in seismic design the utilization of material reserves and the formation of plastic hinges play an important role. In devastating earthquakes in Northridge (USA) and Kobe (Japan) brittle fracture of welded connections in steel moment frames occurred prior to formation of plastic hinges and utilization of plastic material reserves. The subsequent research works resulted in improved design rules and recommendations for these kinds of failure. But to guarantee sufficient ductile performance of these connections also in the upper shelf region, plastic and earthquake resistant design rules should take into account degradation of strain capacity and toughness properties due to quasi static and especially seismic loading. In the scope of the current European project “Plastotough”, the main objective is to derive quantified toughness design rules in the upper shelf based on the strain requirements opposed to strain capacities. This paper gives an overview over the research work in performance and shows recent results from experimental and numerical analyses performed within this project for monotonic and cyclic loading. |
2008
|
Nonn, A.; Dahl, W.; Bleck, W. Numerical modelling of damage behaviour of laser-hybrid welds Werkstoffsimulation Artikel In: Engineering Fracture Mechanics, Bd. 75, Nr. 11, S. 3251 - 3263, 2008, ISSN: 0013-7944, (Local Approach to Fracture (1986–2006): Selected papers from the 9th European Mechanics of Materials Conference). @article{NONN20083251,
title = {Numerical modelling of damage behaviour of laser-hybrid welds},
author = {A. Nonn and W. Dahl and W. Bleck},
url = {http://www.sciencedirect.com/science/article/pii/S0013794407003943},
doi = {https://doi.org/10.1016/j.engfracmech.2007.10.015},
issn = {0013-7944},
year = {2008},
date = {2008-01-01},
journal = {Engineering Fracture Mechanics},
volume = {75},
number = {11},
pages = {3251 - 3263},
abstract = {The effect of laser-hybrid welds on deformation and failure behaviour of fracture mechanics specimens is investigated in order to provide quantitative prediction of damage tolerance and residual strength. The simulation of crack initiation and crack extension in hybrid welds is performed by applying GTN damage model. The identification of damage parameters requires combined numerical and experimental analyses. The tendency to crack path deviation during crack growth depends strongly on the constraint development at the interface between base and weld metal. In order to quantify the influence of local stress state on the crack path deviation, the initial crack location is varied. Finally, the results from fracture mechanics tests are compared to real component, beam-column-connection, with respect to fracture resistance.},
note = {Local Approach to Fracture (1986–2006): Selected papers from the 9th European Mechanics of Materials Conference},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The effect of laser-hybrid welds on deformation and failure behaviour of fracture mechanics specimens is investigated in order to provide quantitative prediction of damage tolerance and residual strength. The simulation of crack initiation and crack extension in hybrid welds is performed by applying GTN damage model. The identification of damage parameters requires combined numerical and experimental analyses. The tendency to crack path deviation during crack growth depends strongly on the constraint development at the interface between base and weld metal. In order to quantify the influence of local stress state on the crack path deviation, the initial crack location is varied. Finally, the results from fracture mechanics tests are compared to real component, beam-column-connection, with respect to fracture resistance. |
2007
|
Nonn, A.; Dahl, W.; Bleck, W. Damage Modelling and Safety Assessment of the Hybrid Welded Structures Werkstoffsimulation Proceedings Article In: 5th German-Japanese Seminar “Materials, Processes and Components”, Fraunhofer Institute for Mechanics of Materials, Freiburg, Germany, 2007. @inproceedings{,
title = {Damage Modelling and Safety Assessment of the Hybrid Welded Structures},
author = {A. Nonn and W. Dahl and W. Bleck},
year = {2007},
date = {2007-06-27},
booktitle = {5th German-Japanese Seminar “Materials, Processes and Components”},
address = {Fraunhofer Institute for Mechanics of Materials, Freiburg, Germany},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
|