@incollection{AltenbergerNosterScholtesetal., author = {Altenberger, Igor and Noster, Ulf and Scholtes, Berthold and Ritchie, Robert O.}, title = {High Temperature Fatigue of Mechanically Surface Treated Materials}, series = {Shot peening}, booktitle = {Shot peening}, editor = {Wagner, Lothar}, publisher = {Wiley-VCH}, address = {Weinheim; [Cambridge]}, isbn = {9783527606580}, doi = {10.1002/3527606580.ch62}, pages = {483 -- 489}, abstract = {Introduction The most well known effect of mechanical surface treatments on metallic materials is the improvement in fatigue properties. It is therefore not surprising that most of the archival literature on mechanical surface treatments, such as shot peening, deep rolling and laser shock peening, deals with the effect of near-surface properties on fatigue behavior. Most of these studies, however, are confined to room temperature fatigue behavior; in comparision, the effect of mechanical surface treatment on fatigue behavior at high temperatures has been rarely investigated [1-5]. The reason for this disparity can be found in the popular belief that fatigue strength improvement by mechanical surface treatments is mainly due to the presence of compressive residual stresses, and since such stresses should anneal out at elevated temperatures, mechanical surface treatments for high temperature applications would appear questionable. However, this view may be over simplistic as there is always a possibility that the residual stresses may be at least partially stable at elevated temperatures [6]; in addition, other factors may be involved, such as the nature of the near-surface microstructure. Accordingly, it is the objective of this study to examine the role of mechanical surface treatments on the high temperature fatigue behavior of several metallic engineering materials. Moreover, it is the aim of this work to clarify what are the critical temperature "thresholds' at which near-surface microstructures and residual stresses become unstable and whether this can explain the observed fatigue behavior.}, language = {en} } @book{AltenbergerWagnerMhaedeetal., author = {Altenberger, Igor and Wagner, Lothar and Mhaede, Mansour and Juijerm, Patiphan and Noster, Ulf}, title = {Effect of Deep Rolling on the Cyclic Performance of Magnesium and Aluminium Alloys in the Temperature Range 20-250°C}, series = {The 10th International Conference on Shot Peening (ICSP), Conference Proceedings, Tokyo Japan, 15th to 18th September, 2008}, journal = {The 10th International Conference on Shot Peening (ICSP), Conference Proceedings, Tokyo Japan, 15th to 18th September, 2008}, abstract = {Mechanical surface treatments such as deep rolling or laser-shock peening can markedly affect the cyclic performance of light-weight alloys, especially if significant thick work hardened surface regions are induced. At room temperature, the cyclic deformation behaviour is strongly influenced by the nature of the induced near-surface microstructures provided that they remain stable during fatigue loading. At elevated temperatures, the stability of near-surface work hardening and local microstructures plays an even more important role since the process-induced residual compressive stresses are likely to anneal out partially or completely. This overview illustrates to what extent deep rolling can effect the cyclic performance of various wrought light alloys being fatigue loaded in stress control at ambient and elevated temperatures.}, language = {en} } @incollection{NosterAltenbergerRitchieetal., author = {Noster, Ulf and Altenberger, Igor and Ritchie, Robert O. and Scholtes, Berthold}, title = {Isothermal Fatigue Behavior and Residual Stress States of Mechanically Surface Treated Ti-6Al-4V: Laser Shock Peening vs. Deep Rolling}, series = {Shot peening}, booktitle = {Shot peening}, editor = {Wagner, Lothar}, publisher = {Wiley-VCH}, address = {Weinheim; [Cambridge]}, isbn = {9783527606580}, doi = {10.1002/3527606580.ch57}, pages = {447 -- 453}, abstract = {In this paper, the high-temperature fatigue behavior and residual stress states of a Ti-6Al-4V alloy are investigated after mechanical surface treatment. In particular, the two surface treatments investigated, laser shock peening and deep rolling, were observed to result in significantly different residual stress states. The consequent isothermal fatigue behavior at elevated temperatures, characterized using cyclic deformation curves, are discussed in terms of the stability of the near-surface work hardening and compressive residual stresses. Despite pronounced relaxation of the residual stresses, both laser shock peening and deep rolling led to a significant improvement in the cyclic deformation behavior and, hence, increased fatigue lifetimes at elevated temperatures as compared to untreated materials states.}, language = {en} } @article{NosterScholtes, author = {Noster, Ulf and Scholtes, Berthold}, title = {Isothermal strain-controlled quasi-static and cyclic deformation behavior of magnesium wrought alloy AZ31}, series = {International Journal of Materials Research / Zeitschrift f{\"u}r Metallkunde}, volume = {94}, journal = {International Journal of Materials Research / Zeitschrift f{\"u}r Metallkunde}, number = {5}, doi = {10.1515/ijmr-2003-0098}, pages = {559 -- 563}, abstract = {The low-cycle and high-cycle fatigue behavior of the Mg-base wrought alloy AZ31 is investigated in the temperature range 20- 300 °C using total-strain-controlled push - pull tests. It is shown that the mechanical properties of the material are substantially influenced by the direction dependent formation of deformation twins and resulting deformation asymmetry. As a consequence tensile mean stresses develop during total-strain-controlled fatigue tests without mean strain.}, language = {en} } @article{BitscheNosterPeterlechner, author = {Bitsche, Robert and Noster, Ulf and Peterlechner, Christian}, title = {F{\"u}gepartner schl{\"u}ssig zu Leichtbaukomponenten verbinden?}, series = {Lightweight Design}, volume = {1}, journal = {Lightweight Design}, number = {2}, publisher = {Springer}, doi = {10.1007/BF03223528}, pages = {30 -- 34}, abstract = {Kombinationen aus kraft- und formschl{\"u}ssigen Verbindungen erh{\"o}hen die Leistung bei im Hybridguss verbundenen Gussteilen mit Anbau- oder Einlegeteilen und machen separate F{\"u}geprozesse {\"u}berfl{\"u}ssig. Simulations-Methoden unterst{\"u}tzen das Design kraft- und formschl{\"u}ssiger Verbindungen. Ergebnisse eines Ausdr{\"u}ckversuchs zeigen eine relativ gute {\"U}bereinstimmung zwischen gemessenen und mittels Simulation ermittelten Kraft-Weg-Kurven.}, language = {de} } @incollection{BillingerNoster, author = {Billinger, Wolfgang and Noster, Ulf}, title = {Bauteilfertigung}, series = {Leichtbau}, booktitle = {Leichtbau}, editor = {Degischer, Hans Peter}, publisher = {Wiley-VCH}, address = {Weinheim}, isbn = {9783527628247}, doi = {10.1002/9783527628247.ch4}, pages = {247 -- 278}, language = {de} } @article{NallaAltenbergerNosteretal., author = {Nalla, Ravi K. and Altenberger, Igor and Noster, Ulf and Liu, G.Y. and Scholtes, Berthold and Ritchie, Robert O.}, title = {On the influence of mechanical surface treatments—deep rolling and laser shock peening—on the fatigue behavior of Ti-6Al-4V at ambient and elevated temperatures}, series = {Materials Science and Engineering: A}, volume = {355}, journal = {Materials Science and Engineering: A}, number = {1-2}, publisher = {Elsevier}, issn = {1873-4936}, doi = {10.1016/S0921-5093(03)00069-8}, pages = {216 -- 230}, abstract = {It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Deep rolling (DR) is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of DR on the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) behavior of a Ti-6Al-4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near-surface microstructures. Preliminary results on laser shock peened Ti-6Al-4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ∼450 °C, i.e. at a homologous temperature of ∼0.4T/Tm (where Tm is the melting temperature). Based on cyclic deformation and stress/life (S/N) fatigue behavior, together with the X-ray diffraction and in situ transmission electron microscopy (TEM) observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti-6Al-4V at such higher temperatures, despite the almost complete relaxation of the near-surface residual stresses. In the absence of such stresses, it is shown that the near-surface microstructures, which in Ti-6Al-4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment.}, language = {en} } @article{NosterScholtes, author = {Noster, Ulf and Scholtes, Berthold}, title = {Bauschingerefekt und mechanische Zwillingsbildung der Magnesiumlegierung AZ31}, series = {H{\"a}rterei-technische Mitteilungen : HTM ; Zeitschrift f{\"u}r Werkstoffe, W{\"a}rmebehandlung, Fertigung}, volume = {58}, journal = {H{\"a}rterei-technische Mitteilungen : HTM ; Zeitschrift f{\"u}r Werkstoffe, W{\"a}rmebehandlung, Fertigung}, publisher = {Hanser}, pages = {322 -- 327}, language = {de} } @article{BartschBurgerGradetal., author = {Bartsch, Alexander and Burger, Moritz and Grad, Marius and Esper, Lukas and Schultheiß, Ulrich and Noster, Ulf and Schratzenstaller, Thomas}, title = {Enhancement of laser cut edge quality of ultra-thin titanium grade 2 sheets by applying an in-process approach using modulated Yb:YAG continuous wave fiber laser}, series = {Discover Mechanical Engineering}, journal = {Discover Mechanical Engineering}, number = {10}, publisher = {Springer}, doi = {10.1007/s44245-023-00018-3}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-65647}, pages = {9}, abstract = {Titanium is used in many areas due to its excellent mechanical, biological and corrosion-resistant properties. Implants often have thin and filigree structures, providing an ideal application for fine cutting with laser. In the literature, the main focus is primarily on investigating and optimizing the parameters for titanium sheets with thicknesses greater than 1 mm. Hence, in this study, the basic manufacturing parameters of laser power, cutting speed and laser pulse of a 200 W modulated fiber laser are investigated for 0.15 mm thick grade 2 titanium sheets. A reproducible, continuous cut could be achieved using 90 W laser-power and 2 mm/s cutting-speed. Pulse pause variations between 85 and 335 μs in 50 μs steps and a fixed pulse width of 50 μs show that a minimum kerf width of 23.4 μm, as well as a minimum cut edge roughness Rz of 3.59 μm, is achieved at the lowest pulse pause duration. An increase in roughness towards the laser exit side, independent of the laser pulse pause duration, was found and discussed. The results provide initial process parameters for cutting thin titanium sheets and thus provide the basis for further investigations, such as the influence of cutting gas pressure and composition on the cut edge.}, language = {en} } @unpublished{GradHaagHahnetal., author = {Grad, Marius and Haag, Lydia and Hahn, Konstantin and Schultheiß, Ulrich and Esper, Lukas and Noster, Ulf}, title = {Influence of carbon content on the formation of TiC at diffusion bonded titanium-steel interface}, publisher = {Elsevier}, doi = {10.2139/ssrn.4261928}, abstract = {Hot pressing of pure Ti and various carbon steels in a temperature range of 950 - 1050 °C creates an up to 9 μm thick compound layer of TiC at the Ti/ steel interface. The calculation of the activation energy for layer formation is 126.5 - 136.7 kJ/mol, independent of the steels carbon content. As the carbon content of the steel increases, the layer thickness also increases, which provides enormous potential for the surface modification of Ti/ Ti-alloys.}, language = {en} }