@misc{SchobRoszakSagradovetal., author = {Schob, Daniela and Roszak, Robert and Sagradov, Ilja and Sparr, Holger and Kupsch, Andreas and Leonard, Fabien and M{\"u}ller, Bernd R. and Bruno, Giovanni}, title = {Experimental and numerical simulation of material and damage behaviour of 3d printed polyamide 12 under quasi-static-loading}, series = {Archives of Mechanics}, volume = {71}, journal = {Archives of Mechanics}, number = {4-5}, issn = {0373-2029}, doi = {10.24423/aom.3162}, pages = {507 -- 526}, abstract = {In order to characterise the material and damage behaviour of additively manufactured polyamide 12 (PA12) under quasi-static load and to implement it in a numerical model, experiments under quasi-static load as well as microstructural investigations were carried out. Selective laser sintering (SLS) was used as the manufacturing process. For the classification of the material behaviour, quasi-static cyclic tests with holding times as well as tensile tests were performed. X-ray refraction and computed tomography (CT) were used to investigate the damage behaviour. The Chaboche model, which has already been applied for metallic materials under thermomechanical loading, served as the basis for the selection of the numerical material model. The same procedure was used for the selection of the damage model, where the Gurson-Tvergaard-Needleman (GTN) model was chosen, which was already used for porous metallic materials. The Chaboche model shows very good agreement with experimental results. Furthermore, the coupling with the GTN model allows a very good modelling of the damage behaviour. Finally, it could be shown that the selected models are suitable to simulate the material and damage behaviour of 3D printed PA12.}, language = {en} } @misc{RoszakSchobSparretal., author = {Roszak, Robert and Schob, Daniela and Sparr, Holger and Ziegenhorn, Matthias}, title = {Analysis of Material Properties Base on Fluid Structure Interaction Simulation}, series = {Proceedings of the 14th International Scientific Conference: Computer Aided Engineering}, journal = {Proceedings of the 14th International Scientific Conference: Computer Aided Engineering}, editor = {Rusiński, Eugeniusz and Pietrusiak, Damian}, edition = {1. Auflage}, publisher = {Springer Nature Switzerland}, address = {Cham}, isbn = {978-3-030-04974-4}, doi = {10.1007/978-3-030-04975-1_70}, pages = {611 -- 618}, abstract = {Paper presents results of dynamic FSI simulation of unmanned aerial vehicle, where for first case, a typical linear material was used, and for second case, a composite material was used. The simulations were performed with the objective of studying model reaction with forces indicated by flow which were defined by initial conditions. Secondary objective was to evaluate critical flutter speed. Simulations provided interesting results: for linear case, applied flow speed resulted with occurrence of flutter phenomena, while composite case exhibited damping of vibration in designated points along the wing. Presented simulations were performed within an environment using loosely-coupled approach. CFD simulations were carried out with use of parallel code DLR-Tau. FSI computations were executed with applied modal approach for structural model and full data exchange between fluid and structure as well as mesh deformation.}, language = {en} } @misc{SparrRoszakSagradovetal., author = {Sparr, Holger and Roszak, Robert and Sagradov, Ilja and Schob, Daniela and Ziegenhorn, Matthias}, title = {Thermo-viscoplastic material modelling for self-heating loads and its experimental verification}, series = {Technische Mechanik}, volume = {40}, journal = {Technische Mechanik}, number = {1}, issn = {2199-9244}, doi = {10.24352/UB.OVGU-2020-015}, pages = {66 -- 76}, abstract = {The paper examines a modelling approach for thermomechanically coupled problems and an experimental concept for a material law validation and verification for self-heating with small to moderate temperature ranges. The study compares two different model formulations and is generally applicable to a variety of material classes. One model is based on a rheological network with an extension for dissipative deformation below the elastic limit. The other model operates without a yield condition. Both models are applied to published experimental data in terms of rate-independent behaviour and the evaluation is carried out on stress-strain-level, temperature evolution and the energy transformation ratio. Furthermore the two models are applied to a strain rate-dependent load case conducted at our institute discussing the same entities. It is pointed out, that the approach of a thermomechanical analysis is valuable and informative to assess the observed deformation processes and to describe the material behaviour with a thermodynamically valid parameter set.}, language = {en} } @misc{SchobSagradovRoszaketal., author = {Schob, Daniela and Sagradov, Ilja and Roszak, Robert and Sparr, Holger and Franke, Rainer and Ziegenhorn, Matthias and Kupsch, Andreas and Leonard, Fabien and M{\"u}ller, Bernd R. and Bruno, Giovanni}, title = {Experimental determination and numerical simulation of material and damage behaviour of 3d printed polyamide 12 under cyclic loading}, series = {Engineering Fracture Mechanics}, volume = {229}, journal = {Engineering Fracture Mechanics}, issn = {0013-7944}, doi = {10.1016/j.engfracmech.2019.106841}, pages = {13}, abstract = {The material and damage behaviour of additively manufactured polyamide 12 under cyclic loading was characterized by cyclic tests and microstructure analysis by using microscopy, X-ray refraction, and computed tomography. The results were used to determine parameters for the viscoplastic material model by Chaboche and a damage model by Gurson-Tvergaard-Needleman. The temperature was monitored during the experiments and the self-heating effect was observed. By including this effect, a higher accuracy could be achieved with the results of mechanical experiments.}, language = {en} } @misc{SagradovSchobRoszaketal., author = {Sagradov, Ilja and Schob, Daniela and Roszak, Robert and Maasch, Philipp and Sparr, Holger and Ziegenhorn, Matthias}, title = {Experimental investigation and numerical modelling of 3D printed polyamide 12 with viscoplasticity and a crack model at different strain rates}, series = {Materials Today Communications}, volume = {25}, journal = {Materials Today Communications}, issn = {2352-4928}, doi = {10.1016/j.mtcomm.2020.101542}, pages = {8}, abstract = {This contribution presents an investigation of strain rate dependent behaviour for selective laser sintered polyamide 12. Two different cases are considered: a strain rate change within tensile loading and a relaxation test incorporating a strain rate change after each holding time section. For the simulation of material behaviour the material model of Bodner-Partom and Chaboche were used. The damage behaviour was considered by the Lemaitre crack model. Thereby it was determined which numerical model is more suitable to reproduce the strain rate-dependent behaviour. Tensile and relaxation tests at constant speeds served as the basis for these investigations.}, language = {en} } @misc{RichterSmolinaPawlaketal., author = {Richter, Lukas and Smolina, Irina and Pawlak, Andrzej and Schob, Daniela and Roszak, Robert and Maasch, Philipp and Ziegenhorn, Matthias}, title = {Thermomechanical analysis of PBF-LB/M AlSi7Mg0.6 with respect to rate-dependent material behaviour and damage effects}, series = {Applied Mechanics}, volume = {5}, journal = {Applied Mechanics}, number = {3}, publisher = {MDPI}, issn = {2673-3161}, doi = {10.3390/applmech5030030}, pages = {533 -- 552}, abstract = {This paper describes the self-heating effects resulting from mechanical deformation in the additively manufactured aluminium alloy AlSi7Mg0.6. The material's self-heating effect results from irreversible changes in the material's microstructure that are directly coupled with the inelastic deformations. These processes are highly dissipative, which is reflected in the heat generation of the material. To describe such effects, a numerical framework that combines an elasto-viscoplastic Chaboche model with the Gurson Tvergaard Needleman damage approach is analysed and thermomechanically extended. This paper characterises the sample preparation, the experimental set-up, the development of the thermomechanical approach, and the material model. A user material subroutine applies the complete material model for the finite element software Abaqus 2022. To validate the material model and the parameters, a complex tensile test is performed. In order to check the finite element model, the energy transformation ratio is included in the evaluation. The numerical analyses of the mechanical stress evolution and the self-heating behaviour demonstrate good agreement with the experimental test. In addition, the calculation shows the expected behaviour of the void volume fraction that rises from the initial value of 0.0373\%to a higher value under a complex mechanical load.}, language = {en} } @misc{SchobRichterKoteckietal., author = {Schob, Daniela and Richter, Lukas and Kotecki, Krzysztof and Kurpisz, Dariusz and Roszak, Robert and Maasch, Philipp and Ziegenhorn, Matthias}, title = {Characterization and Simulation of Shear-Induced Damage in Selective-Laser-Sintered Polyamide 12}, series = {Materials}, volume = {17}, journal = {Materials}, number = {1}, issn = {1996-1944}, doi = {10.3390/ma17010038}, pages = {15}, abstract = {This paper presents the characterisation of selective-laser-sintered (SLS) samples of polyamide 12 (PA12) under shear loading. PA12 is a semi-crystalline thermoplastic and is used in various industries. Its behaviour under shear stress, which is particularly important for product reliability, has not yet been sufficiently investigated. This research focuses on understanding the material and damage behaviour of PA12 under shear-induced stress conditions. The study included quasi-static experiments and numerical simulations. Samples were prepared via SLS and tested according to ASTM standards. Digital image correlation (DIC) was used for precise deformation measurements. The Chaboche material model was used for the viscoplastic behaviour in the numerical simulations. Due to existing material discontinuities in the form of voids, the material model was coupled with the Gurson-Tvergaard-Needleman (GTN) damage model. A modified approach of the GTN model was used to account for low stress triaxiality under shear loading. These models were implemented in MATLAB and integrated into Abaqus via a User Material (UMAT) subroutine. The results of the experiments and simulations showed a high degree of accuracy. An important finding was the significant influence of the shear factor kw on the damage behaviour, especially during failure. This factor proved to be essential for the accurate prediction of material behaviour under shear-induced stress conditions. The integration of the modified GTN model with the Chaboche material model in UMAT enables an accurate prediction of the material and damage behaviour and thus makes an important contribution to the understanding of the mechanical material behaviour of SLS PA12 specimens.}, language = {en} } @misc{KuklaKondejJończyketal., author = {Kukla, Dominik and Kondej, Adam and Jończyk, Sylwester and Lasota, Piotr and Tabin, Jakub and Schob, Daniela and Roszak, Robert and Kawałko, Jakub and Zag{\´o}rski, Andrzej and Kopec, Mateusz}, title = {Eddy current methodology in the non-direct measurement of martensite during plastic deformation of SS316L}, series = {Open engineering}, volume = {15}, journal = {Open engineering}, number = {1}, publisher = {De Gruyter}, address = {Berlin ; Warschau}, issn = {2391-5439}, doi = {10.1515/eng-2025-0118}, pages = {1 -- 9}, abstract = {This study examines the use of various eddy current induction techniques to evaluate the stability of austenite in SS316L steel subjected to plastic deformation. This deformation, which occurs locally in austenitic steel structures under operational loads, leads to a martensitic transformation. This transformation affects both the mechanical and magnetic properties of the steel. The martensitic phase content, being ferromagnetic, can be quantitatively assessed using a ferritoscope and other magnetic induction methods. The research explores techniques based on the analysis of impedance signal changes obtained using the NORTEC defetoscope and the WIROTEST device developed by the author's team. By examining the phase angle, ET signal amplitude, and resonance frequency changes in the eddy current excitation system, the study aims to quantitatively assess the martensitic phase content in samples subjected to plastic deformation. These results were verified through comparison with data from a ferritoscope and X-ray diffraction analysis. Additionally, the eddy current technique facilitates surface screening of the specimen, making it possible to identify cracks and locate the martensitic transformation front in areas of stress concentration.}, language = {en} }