@misc{ImranSzyndlerAfzaletal., author = {Imran, Muhammad and Szyndler, Joanna and Afzal, Muhammad Junaid and Bambach, Markus}, title = {Dynamic recrystallization-dependent damage modeling during hot forming}, series = {International Journal of Damage Mechanics}, volume = {29}, journal = {International Journal of Damage Mechanics}, number = {2}, issn = {1530-7921}, doi = {10.1177/1056789519848477}, pages = {335 -- 363}, language = {en} } @misc{ImranSzyndlerAfzaletal., author = {Imran, Muhammad and Szyndler, Joanna and Afzal, Muhammad Junaid and Bambach, Markus}, title = {Towards the damage evolution for hot forming processes using Gurson-Tvergaard Needleman model - Coupled to dynamic recrystallization}, series = {AIP Conference Proceedings}, volume = {2113}, journal = {AIP Conference Proceedings}, number = {1}, isbn = {978-0-7354-1847-9}, doi = {10.1063/1.5112741}, language = {en} } @misc{BambachSizovaSzyndleretal., author = {Bambach, Markus and Sizova, Irina and Szyndler, Joanna and Bennett, Jennifer and Hyatt, Greg and Cao, Jian and Papke, Thomas and Merklein, Marion}, title = {On the hot deformation behavior of Ti-6Al-4V made by additive manufacturing}, series = {Journal of Materials Processing Technology}, volume = {288}, journal = {Journal of Materials Processing Technology}, issn = {0924-0136}, doi = {10.1016/j.jmatprotec.2020.116840}, language = {en} } @misc{ApelHaertelSzyndler, author = {Apel, Markus and H{\"a}rtel, Sebastian and Szyndler, Joanna}, title = {Prediction of the microstructure morphology after the WAAM process based on the FEM simulation results}, series = {Materials Research Proceedings}, volume = {41}, journal = {Materials Research Proceedings}, doi = {10.21741/9781644903131-3}, pages = {22 -- 31}, abstract = {To improve understanding of the material behavior of additive-produced components, this paper focuses on the development of a numerical model that reproduces a Wire Arc Additive Manufacturing (WAAM) process, with particular attention given to the evolution of the microstructure. In this study, a finite element model in Simufact Welding software is developed, that replicates a real wire arc welding process of building a multilayer straight wall. Microscopy analysis of the weld wall cut in the middle of its length gave information about the expected microstructure morphology at different levels of the build wall. The whole experimental setup is reproduced in the software Simufact Welding. Simulation results in the form of temperature-time and temperature gradient-time history are then used as superimposed thermal conditions to simulate the microstructure evolution at different areas of the welded part by using MICRESS software.}, language = {en} } @misc{HaertelSzyndlerPakdelSefidietal., author = {H{\"a}rtel, Sebastian and Szyndler, Joanna and Pakdel Sefidi, Moein and J{\"a}ger, Reyk}, title = {Prediction of the evolution of material properties during the AM process based on the FEM simulation and experimental results}, series = {Materials Research Proceedings}, volume = {41}, journal = {Materials Research Proceedings}, doi = {10.21741/9781644903131-5}, pages = {40 -- 49}, abstract = {To deepen the understanding of material behavior after additive manufacturing, this article focuses on the prediction of material properties after the Wire Arc Additive Manufacturing (WAAM) process. Particular attention is put on the temperature curves in the various phases of the welding process, which influence the final material properties, especially the hardness of the resulting part. A total of nine components in the form of walls were produced using the WAAM process, with the number of layers varying from 1 to 9. By experimentally analyzing the welded parts, which were cut in the middle of their length, it was possible to gain insights into the development of hardness at selected points. The entire test setup was simulated in the Simufact Welding FE-software. The simulation results in the form of temperature-time diagrams were then correlated with the real hardness measurements at the corresponding points. In this way, a model was developed that for the first time considers the development of hardness as a result of cooling after the welding process as well as the change in hardness as a result of reheating due to the application of additional layers.}, language = {en} } @misc{SzyndlerSchmidtHaertel, author = {Szyndler, Joanna and Schmidt, Alexander and H{\"a}rtel, Sebastian}, title = {Determination of welding heat source parameters for fem simulation based on temperature history and real bead shape}, series = {Material Forming : The 26th International ESAFORM Conference on Material Forming, Krak{\´o}w, Poland, April 19-21, 2023}, journal = {Material Forming : The 26th International ESAFORM Conference on Material Forming, Krak{\´o}w, Poland, April 19-21, 2023}, edition = {28}, doi = {10.21741/9781644902479-18}, pages = {159 -- 168}, language = {en} } @misc{SzyndlerHaertelBambach, author = {Szyndler, Joanna and H{\"a}rtel, Sebastian and Bambach, Markus}, title = {Machine learning of the dynamics of strain hardening based on contact transformations}, series = {Journal of Intelligent Manufacturing}, volume = {2025}, journal = {Journal of Intelligent Manufacturing}, publisher = {Springer}, doi = {10.1007/s10845-025-02577-6}, pages = {22}, abstract = {Dislocation density-based models offer a physically grounded approach to modeling strain hardening in metal forming. Since these models are typically defined by Ordinary Differential Equations (ODEs), their accuracy is constrained by both, the model formulation and the parameter identification process. Machine Learning (ML) provides an alternative by allowing models to be constructed directly from experimental data, bypassing the accuracy limitations of explicitly defined models. However, applying ML to ODEs introduces the need for novel training techniques. This work presents a new approach for developing neural ODE models for flow curve description, utilizing a contact transformation to simplify the problem of learning an ODE into a learning a multivariate function.}, language = {en} } @misc{GruegerSzyndlerJenschetal., author = {Gr{\"u}ger, Lennart and Szyndler, Joanna and Jensch, Felix and H{\"a}rtel, Sebastian}, title = {Porosity analysis of L-PBF manufactured AZ91D components}, series = {Materials research proceedings}, volume = {54}, journal = {Materials research proceedings}, publisher = {Materials Research Forum LLC}, address = {Millersville, PA}, isbn = {978-1-64490-359-9}, issn = {2474-395X}, doi = {10.21741/9781644903599-22}, pages = {199 -- 208}, abstract = {Several materials for joint replacement parts approved in medical technology are being investigated. Magnesium alloys are very suitable for implants due to the similar strength properties between magnesium alloys and human bone. Therefore, the present work aims to examine the parameters for producing the magnesium alloy AZ91D. For this purpose, 16 samples were manufactured with varying laser power and exposure speed and examined using µCT analyses. As a result, densities between 99.56 and 95.21 percent were achieved. The samples with the lowest density were subjected to a HIP process to increase the relative density. However, a further µCT analysis revealed only minor positive effects of the HIP process. An analysis of the number and size of the pores indicates that the pores bonded together instead of being closed.}, language = {en} } @misc{EmdadiJenschSzyndleretal., author = {Emdadi, Aliakbar and Jensch, Felix and Szyndler, Joanna and Huang, Hsuan-Po and H{\"a}rtel, Sebastian and Weiß, Sabine}, title = {Void closure behavior during hot forming of an Fe-Al alloy}, series = {Materials research proceedings}, volume = {54}, journal = {Materials research proceedings}, publisher = {IWA Publishing}, address = {Millersville, PA}, isbn = {978-1-64490-359-9}, issn = {2474-395X}, doi = {10.21741/9781644903599-99}, pages = {927 -- 935}, abstract = {Hot forging is a forming process that can be used as a post-processing treatment to close residual porosity and refine the microstructure of additively manufactured materials, resulting in improved mechanical properties. During hot forging, void closure occurs through plastic deformation resulting from a predominantly compressive stress state at elevated temperatures. In the present work, Fe-25Al-1.5Ta (at. \%) samples have been produced by laser powder bed fusion (LPBF) using a larger layer thickness and scan speed than commonly used to achieve a target porosity fraction of approximately 10\%. Full densification is attempted in the subsequent hot compression step at various height reduction ratios. The as-built LPBF samples contained 8-10\% voids. After deformation to true strains of 0.2, 0.4, and 0.6, the void fraction decreased significantly to approximately 4\%, 2.3\%, and 1.1\%, respectively. Hot compression resulted in the complete closure of large pores with a size range of 200-300 µm and a significant reduction in the size of small to medium pores. These results show potential for improving the productivity of the LPBF by speeding up the process by increasing layer thickness and scanning speed while maintaining a reasonable density. Full densification should be achieved by subsequent hot forging.}, language = {en} } @misc{EmdadiYangSzyndleretal., author = {Emdadi, Aliakbar and Yang, Yitong and Szyndler, Joanna and Jensch, Felix and Ertugrul, G{\"o}khan and Tovar, Michael and H{\"a}rtel, Sebastian and Weiß, Sabine}, title = {Highly printable Fe₃Al intermetallic alloy}, series = {Metals : open access journal}, volume = {16}, journal = {Metals : open access journal}, number = {5}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/met16010005}, pages = {1 -- 15}, abstract = {Intermetallic Fe₃Al-based alloys reinforced with Laves-phase precipitates are emerging as potential replacements for conventional high-alloy steels and possibly polycrystalline Ni-based superalloys in structural applications up to 700 °C. Their impressive mechanical properties, however, are offset by limited fabricability and poor machinability due to their severe brittleness. High tool wear during finish-machining, which is still required for components such as turbine blades, remains a key barrier to their broader adoption. In contrast to conventional manufacturing routes, additive manufacturing offers a viable solution by enabling near-net-shape manufacturing of difficult-to-machine iron aluminides. In the present study, laser powder bed fusion was used to produce an Fe-25Al-1.5Ta intermetallic containing strengthening Laves-phase precipitates, and the porosity, microstructure and phase composition were characterized as a function of the process parameters. The results showed that preheating the build plate to 650 °C effectively suppressed delamination and macrocrack formation, even though noticeable cracking still occurred at the high scan speed of 1000 mm/s. X-ray tomography revealed that samples fabricated with a lower scan speed (500 mm/s) and a higher layer thickness (0.1 mm) contained larger, irregularly shaped pores, whereas specimens printed at the same volumetric energy density (40 J/mm3) but with different parameter sets exhibited smaller fractions of predominantly spherical pores. All samples contained mostly elongated grains that were either oriented close to <001> relative to the build direction or largely texture-free. X-ray diffraction confirmed the presence of Fe₃Al and C14-type (Fe, Al)₂Ta Laves phase in all samples. Hardness values fell within a narrow range (378-398 HV10), with only a slight reduction in the specimen exhibiting higher porosity.}, language = {en} }