Publikationen

@inproceedings{Nonn2012,

title = {Simulation of ductile crack propagation in high-strength pipeline steel using damage models},

author = {A. Nonn and C. Kalwa},

year  = {2012},

date = {2012-09-24},

booktitle = {9th International Pipeline Conference 2012 (IPC 2012)},

address = {Calgary, Canada},

abstract = {The performance of engineering design of high-strength steel pipelines has revealed the necessity to revise current design procedures. Therefore, an improved and detailed comprehension of fracture mechanisms and development of failure prediction tools are required in order to derive new design criteria. In last decades the most successful failure prediction tools for steel structures subjected to various type of loading can be encountered in the field of damage mechanics. This paper aims to describe ductile fracture behavior of high-strength steel pipelines by applying three different damage models, Gurson-Tvergaard-Needelman (GTN), Fracture Locus Curve (FLC) and Cohesive Zone (CZ). These models are evaluated regarding their capability to estimate ductile crack propagation in laboratory specimens and linepipe components without adjusting the calibrated parameters. It can be shown that appropriate parameter sets can be identified to reproduce load-deformation and fracture resistance curves accurately. The strain rate effect on the fracture behavior is examined by dynamic tests on the BDWT specimens. Finally, the shortcomings of the applied models are pointed out with the reference to possible extensions and modifications.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Schmid2012,

title = {Diminution of mass of different types of fibre reinforcements due to thermal load. },

author = {V. Schmid and B. Jungbauer and M. Romano and I. Ehrlich and N. Gebbeken},

editor = {J. Mottok and O. Ziemann},

isbn = {978-3-8440-1093-0},

year  = {2012},

date = {2012-06-25},

booktitle = {Applied Research Conference 2012 – ARC 2012},

pages = {231--235},

publisher = {Shaker-Verlag},

abstract = {The determination of the fibre volume content in fibre reinforced plastics is usually done by removing the matrix of a representative specimen after the material has been produced. For the removal of a polymeric matrix system two possibilities exist. The matrix can either be extracted chemically or thermally where the fibre reinforcement must not be affected. In the following the applicability of thermally removing the matrix for basalt fibre reinforced plastics is examined. Therefore the diminution of mass of different types of fibre reinforcements is experimentally investigated. The thermal removal of a polymeric matrix system is shown to be suitable for basalt fibre reinforced plastics as well as for glass fibre reinforced plastics.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Schmid2012b,

title = {The influence of different types of fabrics on the fibre volume content and porosity in basalt fibre reinforced plastics.},

author = {V. Schmid and B. Jungbauer and M. Romano and I. Ehrlich and N. Gebbeken},

editor = {J. Mottok and O. Ziemann},

isbn = {978-3-8440-1093-0},

year  = {2012},

date = {2012-06-25},

booktitle = {Applied Research Conference 2012 – ARC 2012},

pages = {162--165},

publisher = {Shaker-Verlag},

abstract = {High quality semi-finished products with reproducible properties of basaltic fibres are hardly available on the market. In order to examine the properties of basalt fibre reinforced plastics high quality specimens are necessary. The fibre volume content and the porosity of the produced specimen are used as the typical criteria to evaluate the achieved quality of the produced material. The effect of the geometrical properties of the different semi-finished products on the fibre volume contents is relatively small whereas the porosity content is considerably affected.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Kofiani2012,

title = {Experiments and fracture modeling of high-strength pipelines for high and low stress triaxiality},

author = {K. Kofiani and A. Nonn and T. Wierzbicki and C. Kalwa and C. Walters},

year  = {2012},

date = {2012-06-17},

booktitle = {The 22nd  International Society of Offshore and Polar Engineering 2012 (ISOPE 2012)},

address = {Rhodes, Greece},

abstract = {This paper provides results from a comprehensive study on mechanical characterization of high-strength pipeline steel, grade X100 using experimental and numerical methods. The material was characterized for anisotropic plasticity, fracture initiation for various states of stress, (pre-cracked) fracture toughness and uncracked ductility. The experimental program included tests on flat butterfly-shaped, central hole, notched and circular disk specimens for low stress triaxiality levels; as well as tests on round notched bar specimens and SENT fracture mechanics tests, for high values of stress triaxiality. This program covered a wide range of stress conditions and demonstrated its effect on the material resistance. Parallel to the experimental study, detailed numerical investigations were carried out to simulate all different experimental tests. Using an inverse method, a 3-parameter calibration was performed on the Modified Mohr-Coulomb (MMC) fracture model. Subsequently, the predictive capabilities of the MMC were evaluated by the comparison to the fracture toughness tests results, used extensively in the pipeline industry. The capabilities of the MIT fracture model have been demonstrated on an example of high strength offshore steel, X100. The outcome of this study was not only to provide, the overall characterization of the fracture behavior of this material as an example, but also to present the methodology on how to use the MMC model as a practical tool in pipeline design.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Nonn2012b,

title = {Failure modeling of pipeline X100 Material in temperature transition region},

author = {A. Nonn and C. Kalwa},

year  = {2012},

date = {2012-06-17},

booktitle = {The 22nd International Society of Offshore and Polar Engineering 2012 (ISOPE 2012)},

address = {Rhodes, Greece},

abstract = {This paper focuses on the characterization of the fracture performance of X100 material in transition temperature region using both experimental and numerical methods. The ductile fracture has been analyzed using tests on round notched bar specimens and standard fracture mechanics tests performed at room temperature. In previous publications the damage model Gurson-Tvergaard-Needleman (GTN) has been applied and verified by existing experimental data to describe ductile fracture behavior. The brittle fracture and the fracture in temperature transition region have been studied by means of deep and shallow notched SENB specimens at two different temperatures T=-80°C and -40°C. Besides elastic-plastic analyses to quantify constraint levels for different initial crack configurations at the onset of cleavage fracture, the brittle failure has been described using modified Beremin model. The influence of the stable crack growth on the cleavage failure probability in temperature transition region has been captured by coupling the ductile fracture model (GTN) with the modified Beremin model. Finally, examples have been presented for the practical application of the numerical results on the fracture assessment of the flawed high-strength pipelines.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Ottawa2012,

title = {The influence of ondulation in fabric reinforced composites on dynamic properties in a mesoscopic scale.},

author = {P. Ottawa and M. Romano and I. Ehrlich and M. Wagner and N. Gebbeken},

year  = {2012},

date = {2012-01-01},

booktitle = {11. LS-DYNA Forum},

address = {Ulm},

abstract = {Structural mechanic properties of fiber reinforced plastics depend on the single components’ 

properties, namely matrix and fiber [5]. Simple micromechanic homogenization theories reach a limit 

when a laminate consists of fabric reinforced layers instead of unidirectional layers. The ondulations of 

warp and fill yarn caused by the textile semi-finished product are the reason why the mesoscopic 

scale, which is in between the microscopic and the macroscopic scale, has to be taken into account 

when mechanically characterizing fabric reinforced composites [3]. In this scale a mesomechanic 

kinematic can be derived analytically. Especially, when considering free damped vibrations of 

structures the repeated acting of the kinematic correlation significantly affects the damping behaviour 

to higher values compared to theoretically predicted damping ratios. The model is investigated using 

Finite-Element-Analyses and basically validated experimentally. },

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {The effect of microstructure, strain hardening and strain rate on the fracture behavior of high strength pipeline steels},

author = {A. Nonn and C. Kalwa},

year  = {2011},

date = {2011-08-31},

booktitle = {2nd International Conference on Material Modelling (ICMM2)},

address = {Paris, France},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@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}

}

@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}

}

@inproceedings{,

title = {Failure modeling of hybrid-laser welds in transition temperature region},

author = {A. Nonn},

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},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@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}

}

@inproceedings{,

title = {Numerical and experimental analyses of damage behaviour of steel moment connections},

author = {A. Nonn and W. Dahl and W. Bleck},

year  = {2007},

date = {2007-06-11},

booktitle = {MatMod2007, Material Models – from Nano to Macro, International Workshop},

address = {Hamburg, Germany},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {Lokale Spannungsanalyse bei Rissinitiierung},

author = {A. Nonn and A. Völling},

year  = {2006},

date = {2006-10-04},

booktitle = {4. Workshop Kompetenzverbund Kerntechnik „Komponentensicherheit und Werkstoffverhalten"},

address = {MPA Stuttgart, Germany},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {Failure Behaviour of Hybrid-Laser Welds},

author = {A. Bajric and W. Dahl},

year  = {2006},

date = {2006-07-03},

booktitle = {Fracture of Nano and Engineering Materials and Structures Fracture of Nano and Engineering Materials and Structures, Proceedings of the 16th European Conference on Fracture},

address = {Alexandroupolis, Greece},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {Numerical modelling of damage beahviour in laser-hybrid welds},

author = {A. Bajric and W. Dahl},

year  = {2006},

date = {2006-05-09},

booktitle = {9th European Mechanics of Material Conference (EUROMECH-MECAMAT 2006), Local Approach to Fracture},

address = {Moret-Sur-Loing, France},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {Experimental and Numerical Investigations of the Failure Behaviour of Hybrid Laser Welds},

author = {A. Bajric and W. Brocks and W. Dahl and J. Heyer and P. Langenberg},

year  = {2005},

date = {2005-07-07},

booktitle = {4th German-Japanese Seminar „Materials, Processses and Components“},

address = {University of Karlsruhe, Germany},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {Numerical simulation of crack extension in electron-beam and hybrid-laser welds},

author = {A. Bajric},

year  = {2005},

date = {2005-04-20},

booktitle = {ESIS TC1/TC8 Meeting, Serco Assurance},

address = {Warrington, United Kingdom},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {Investigations of failure behaviour of flawed steel specimens with electron beam welds (EBW)},

author = {A. Bajric and W. Brocks and W. Dahl and J. Heyer and P. Langenberg},

year  = {2005},

date = {2005-03-20},

booktitle = {11th International Congress on Fracture (ICF11)},

address = {Turin, Italy},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {Numerische Simulation des Rissauswanderns (RA) in Strahlschweißverbindungen},

author = {A. Bajric and W. Brocks and W. Dahl and J. Heyer and P. Langenberg},

year  = {2005},

date = {2005-02-22},

booktitle = {DVM-Bericht 237, 37. Tagung des DVM-Arbeitskreises Bruchvorgänge, „Technische Sicherheit, Zuverlässigkeit und Lebensdauer“},

address = {Hamburg, Germany},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{,

title = {Numerical Investigations on Failure Behaviour of Flawed Steel Components Containing Power Beam Welds},

author = {J. Heyer and A. Bajric and W. Dahl and P. Langenberg},

year  = {2003},

date = {2003-12-09},

booktitle = {ESIS TC1/TC8 Meeting},

address = {GKSS Geesthacht},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}