@article{XueKeimParedesetal., author = {Xue, Lufeng and Keim, Vincent and Paredes, M. and Nonn, Aida and Wierzbicki, Tomasz}, title = {Anisotropic effects on crack propagation in pressurized line pipes under running ductile fracture scenarios}, series = {Engineering fracture mechanics}, volume = {249}, journal = {Engineering fracture mechanics}, publisher = {Elsevier}, doi = {10.1016/j.engfracmech.2021.107748}, abstract = {The current analyses present results of running ductile fracture propagation in high strength X100 line pipe steels under the influence of anisotropy. Mechanical anisotropy is commonly available in pipe products as a result of the manufacturing process, especially, those subjected to hot/cold-worked deformation. The outcomes of the present analyses show that its effect on the behavior of running ductile fracture in cracked pipes undergoing depressurization is meaningful. For instance, the Crack-Tip Opening Angle (CTOA) not only exhibits a strong dependence to the pipe's diameter size, but also to the material's anisotropy nature when compared to a hypothetical isotropic material. Moreover, laboratory scale tests such as those performed on Battelle Drop Weight Tear (BDWT) samples provide useful information about initiation of ductile crack propagation when the anisotropy features are taken into account in the material description.}, language = {en} } @inproceedings{KeimNonnLenzetal., author = {Keim, Vincent and Nonn, Aida and Lenz, D. and Brinnel, Viktoria and M{\"u}nstermann, Sebastian}, title = {Simulation of the ductile fracture behaviour of high toughness pipeline steels using combined damage models}, series = {Proceedings of the conference on Technology for future and ageing piplines, Ghent, Belgium}, booktitle = {Proceedings of the conference on Technology for future and ageing piplines, Ghent, Belgium}, language = {en} } @inproceedings{ParedesKeimNonnetal., author = {Paredes, Marcelo and Keim, Vincent and Nonn, Aida and Wierzbicki, Tomasz}, title = {Effect of plasticity parameter on the crack propagation in steel pipelines}, series = {Proceedings of the conference on Technology for future and ageing piplines, Ghent, Belgium}, booktitle = {Proceedings of the conference on Technology for future and ageing piplines, Ghent, Belgium}, language = {en} } @article{KeimMarxNonnetal., author = {Keim, Vincent and Marx, P. and Nonn, Aida and M{\"u}nstermann, Sebastian}, title = {Fluid-structure-interaction modeling of dynamic fracture propagation in pipelines transporting natural gases and CO2-mixtures}, series = {International Journal of Pressure Vessels and Piping}, volume = {175}, journal = {International Journal of Pressure Vessels and Piping}, number = {August}, publisher = {Elsevier}, doi = {10.1016/j.ijpvp.2019.103934}, abstract = {As part of current design standards, the Battelle Two-Curve Model (BTCM) is still widely used to predict and secure ductile crack arrest in gas transmission pipelines. For modern linepipe steels and rich natural gases or CO2 mixtures, the BTCM might lead to incorrect predictions. On the one hand, it suffers from the insufficient description of the individual physical processes in the pipe material and fluid itself. Furthermore, the model does not account for fluid-structure-interaction (FSI) effects during simultaneous running-ductile fracture (RDF) and mixture decompression. Numerical FSI models allow for a more sophisticated, coupled analysis of the driving forces for the failure of pipelines. This paper deals with the development of an FSI model for the coupled prediction of 3D pressure profiles acting on the inner pipe wall during crack propagation. The coupled Euler-Lagrange (CEL) method is used to link the fluid and structure models. In a Lagrange formulation, the modified Bai-Wierzbicki (MBW) model describes the plastic deformation and ductile fracture as a function of the underlying stress/strain conditions. The fluid behavior is calculated in a 3D model space by Euler equations and the GERG-2008 reference equation of state (EOS). The coupled CEL model is used to predict the RDF in small-diameter pipe sections for different fluid mixtures. The calculated 3D pressure distributions ahead and behind the running crack tip (CT) significantly differ in axial and circumferential directions depending on the mixture composition. The predicted FSI between the pipe wall and fluid decompression in 3D CEL/FSI model provides reliable knowledge about the pressure loading of the pipeline during RDF.}, subject = {Fluid-Struktur-Wechselwirkung}, language = {en} } @inproceedings{NonnParedesKeimetal., author = {Nonn, Aida and Paredes, Marcelo and Keim, Vincent and Wierzbicki, Tomasz}, title = {Comparison of Fracture Models to Quantify the Effects of Material Plasticity on the Ductile Fracture Propagation in Pipelines}, series = {Proceedings of the 2018 12th International Pipeline Conference, Volume 3: Operations, Monitoring, and Maintenance, Materials and Joining, September 24-28, 2018, Calgary, Alberta, Canada}, booktitle = {Proceedings of the 2018 12th International Pipeline Conference, Volume 3: Operations, Monitoring, and Maintenance, Materials and Joining, September 24-28, 2018, Calgary, Alberta, Canada}, doi = {10.1115/IPC2018-78366}, abstract = {Various numerical approaches have been developed in the last years aimed to simulate the ductile fracture propagation in pipelines transporting CO2 or natural gas. However, a reliable quantification of the influence of material plasticity on the fracture resistance is still missing. Therefore, more accurate description of the material plasticity on the ductile fracture propagation is required based on a suitable numerical methodology. In this study, different plasticity and fracture models are compared regarding the ductile fracture propagation in X100 pipeline steel with the objective to quantify the influence of plasticity parameters on the fracture resistance. The plastic behavior of the investigated material is considered by the quadratic yield surface in conjunction with a non-associated quadratic plastic flow potential. The strain hardening can be appropriately described by the mixed Swift-Voce law. The simulations of ductile fracture are conducted by an uncoupled, modified Mohr-Coulomb (MMC) and the micromechanically based Gurson-Tvergaard-Needleman (GTN) models. In contract to the original GTN model, the MMC model is capable of describing ductile failure over wide range of stress states. Thus, ductile fracture resistance can be estimated for various load and fracture scenarios. Both models are used for the simulation of fracture propagation in DWTT and 3D pressurized pipe sections. The results from the present work can serve as a basis for establishing the correlation between plasticity parameters and ductile fracture propagation.}, language = {en} } @article{KeimParedesNonnetal., author = {Keim, Vincent and Paredes, Marcelo and Nonn, Aida and M{\"u}nstermann, Sebastian}, title = {FSI-simulation of ductile fracture propagation and arrest in pipelines}, series = {International Journal of Pressure Vessels and Piping}, volume = {182}, journal = {International Journal of Pressure Vessels and Piping}, number = {May}, publisher = {Elsevier}, doi = {10.1016/j.ijpvp.2020.104067}, abstract = {The fracture propagation and arrest control for pipelines transporting rich natural gases and high vapor pressure liquids is based on the Battelle Two-Curve Model (BTCM). Distinct limitations of this model were demonstrated for past and modern steels and gas mixtures. These can be related to the insufficient description of individual physical processes and interactions between the pipe material and transported mixture during the running ductile fracture. In the past, fluid-structure interaction (FSI) models enabled a more sophisticated, coupled analysis of the failure scenario. To quantify their capability of describing the multi-physical processes, the FSI models need to be verified by experimental data from full-scale burst tests (FSBT). Therefore, this paper deals with the simulation of five FSBTs from the literature on API grade X65 pipes with different pipe geometries, mixtures and initial conditions. The FSI is modeled by the coupled Euler-Lagrange (CEL) method. The modified Mohr-Coulomb (MMC) model is implemented in the CEL framework to describe the deformation and ductile fracture in the X65/L450 pipes. 3D Euler equations are used to calculate the mixture decompression with the GERG-2008 equation of state defining the volumetric behavior of a CO2-rich mixture, CH4 and H2. The extended model considers the effect of soil backfill on the pipe deformation and inertia. The numerical predictions agree well with the experimental findings in terms of the crack propagation speed and arrest length underlining the capability of the developed numerical tool.}, subject = {Bruchmechanik}, language = {en} } @article{RajaramanKeimPondicherryetal., author = {Rajaraman, Dhanraj and Keim, Vincent and Pondicherry, Kannaki and Nonn, Aida and Hertele, Stijn and Fauconnier, Dieter}, title = {Stress state characterization of ductile materials during scratch abrasion}, series = {Wear}, volume = {476}, journal = {Wear}, number = {15}, publisher = {Elsevier}, doi = {10.1016/j.wear.2021.203712}, abstract = {Abrasive wear limits the lifetime of many machine components. Most empirical models relate the abrasive wear resistance to material hardness. In reality, however, other material properties are also influencing as scratch abrasion damage follows from a highly complex stress trajectory upon scratching. Numerical (finite element) simulation of scratch abrasion requires the use of a material damage model, which translates this stress trajectory into material degradation and removal. Most damage models include the first two stress invariants. However, fully incorporating the complex stress trajectories that occur during scratch abrasion may require damage models with dependence of the third deviatoric parameter (Lode angle). This paper serves as an a-priori study to evaluate the stress states that may occur during scratch abrasion. Three mechanisms (ploughing, wedging, cutting) are considered. Hereto, the results of an extensive parametric study using elastic-plastic finite element simulations of a scratch indentation process are discussed. Complex, non-proportional variations in stress state values are observed to occur during scratch abrasion. Distinct stress state trajectories are identified for the three abovementioned mechanisms. These variations are critically discussed to motivate a selection of suitable damage models for rigorous finite element analysis of the wear processes associated with scratch abrasion.}, language = {en} } @article{KeimNonnMuenstermann, author = {Keim, Vincent and Nonn, Aida and M{\"u}nstermann, Sebastian}, title = {Application of the modified Bai-Wierzbicki model for the prediction of ductile fracture in pipelines}, series = {International Journal of Pressure Vessels and Piping}, volume = {171}, journal = {International Journal of Pressure Vessels and Piping}, number = {March}, publisher = {Elsevier}, doi = {10.1016/j.ijpvp.2019.02.010}, pages = {104 -- 116}, abstract = {The complex mechanical and corrosive loads of modern pipeline systems transporting oil, natural gas and CO2 impose steadily increasing requirements on material properties. The majority of current design standards still limit the application of modern high toughness linepipe steels due to the simple specification of material requirements in terms of energy levels from Charpy impact or Battelle Drop-Weight-Tear (BDWT) tests. In consequence, research activities have been conducted recently aiming at developing modified or novel experimental methods for the characterization of the ductile fracture behavior. To quantify the effects of various parameters on fracture behavior and derive suitable correlations, it is necessary to accompany these activities by numerical simulations with appropriate ductile damage models. In this paper, the MBW model is applied to study the structural behavior of pipelines in ductile fracture regime. Due to its precise incorporation of the underlying load conditions, the damage model is successfully used to simulate the slant fracture behavior in Battelle Drop weight tear test specimens and pipe sections. In comparison to ductile damage models applied in former studies, namely the Gurson-Tvergaard-Needleman and Cohesive Zone model, the presented numerical methodology allows for a more detailed investigation of loading, material and geometry effects on fracture and crack arrest behavior of pipelines.}, language = {en} } @article{KeimCerroneNonn, author = {Keim, Vincent and Cerrone, Albert R. and Nonn, Aida}, title = {Using local damage models to predict fracture in additively manufactured specimens}, series = {International Journal of Fracture}, volume = {218}, journal = {International Journal of Fracture}, number = {1}, publisher = {Springer Nature}, doi = {10.1007/s10704-019-00371-z}, pages = {135 -- 147}, abstract = {This paper explores the efficacy of employing local damage models, normally applied to ductile material systems manufactured by subtractive techniques, to additively manufactured laboratory specimens. While these specimens were ductile and metallic, their additive character (i.e. porosity and surface roughness) could have had potential to activate multiple life-limiting failure paths, thus obfuscating failure prediction. Herein, two damage models are considered and compared: the micromechanical Gurson-Tvergaard-Needleman model and a Crack Band model of the strain-based, phenomenological genre. Simulations used to calibrate elastic and plastic material properties and predict damage in a novel, non-standard specimen were quasi-static, explicit. Both damage models proved capable in resolving the experimentally-observed failure path and associated loading conditions. The analyses described herein were made as part of the Third Sandia Fracture Challenge.}, language = {en} }