TY - JOUR A1 - Noster, Ulf A1 - Scholtes, Berthold T1 - Bauschingerefekt und mechanische Zwillingsbildung der Magnesiumlegierung AZ31 JF - Härterei-technische Mitteilungen : HTM ; Zeitschrift für Werkstoffe, Wärmebehandlung, Fertigung Y1 - 2003 UR - https://www.researchgate.net/publication/285130307_Bauschingerefekt_und_mechanische_Zwillingsbildung_der_Magnesiumlegierung_AZ31 VL - 58 SP - 322 EP - 327 PB - Hanser ER - TY - CHAP A1 - Noster, Ulf A1 - Altenberger, Igor A1 - Ritchie, Robert O. A1 - Scholtes, Berthold ED - Wagner, Lothar T1 - Isothermal Fatigue Behavior and Residual Stress States of Mechanically Surface Treated Ti-6Al-4V: Laser Shock Peening vs. Deep Rolling T2 - Shot peening N2 - 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. Y1 - 2003 SN - 9783527606580 U6 - https://doi.org/10.1002/3527606580.ch57 SP - 447 EP - 453 PB - Wiley-VCH CY - Weinheim; [Cambridge] ER - TY - JOUR A1 - Nalla, Ravi K. A1 - Altenberger, Igor A1 - Noster, Ulf A1 - Liu, G.Y. A1 - Scholtes, Berthold A1 - Ritchie, Robert O. T1 - 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 JF - Materials Science and Engineering: A N2 - 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. KW - Deep rolling KW - Elevated temperature behavior KW - Fatigue KW - Laser shock peening KW - Residual stress KW - Surface treatment KW - Ti–6Al–4V Y1 - 2003 U6 - https://doi.org/10.1016/S0921-5093(03)00069-8 SN - 1873-4936 VL - 355 IS - 1-2 SP - 216 EP - 230 PB - Elsevier ER - TY - CHAP A1 - Altenberger, Igor A1 - Nalla, R. K. A1 - Noster, Ulf A1 - Scholtes, Berthold A1 - Ritchie, Robert O. T1 - On the fatigue behavior and associated effect of residual stresses in deep rolled and laser shock peened Ti-6Al-4V at ambient and elevated temperatures T2 - 2003 TMS annual meeting N2 - 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 is an especially attractive technique since it is possible to generate deep, near-surface compressive residual stresses and work hardening while retaining a relatively smooth surface finish. Indeed, this technique is best known for increasing the fatigue strength and lifetime of steel components such as crankshafts. Although most work on deep rolling has been on steels, recently it has also been applied with reasonable success to titanium alloys. Accordingly, in this investigation, we examine the effect of deep rolling on the high-cycle fatigue behavior of Ti-6Al-4V, with particular emphasis on the thermal and mechanical stability of the residual stress states and near-surface microstructures. Preliminary results on laser shock peened Ti-6Al-4V are also presented for comparison. In addition, we examine whether these surface treatments are effective in retaining fatigue strength at the higher temperatures of 300 to 450C. Based on the cyclic deformation and stress/life behavior, together with the X-ray and microstructural observations, it is 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 residual stresses at the surface. This clearly implies that, in addition to residual stresses, near-surface microstructures, which in Ti-6Al-4V consist of ultrafine near-surface nanostructures, play a critical role in the enhancement of fatigue lifetimes by mechanical surface treatments. Y1 - 2003 UR - https://www.researchgate.net/publication/273462702_On_the_fatigue_behavior_and_associated_effect_of_residual_stresses_in_deep_rolled_and_laser_shock_peened_Ti-6Al-4V_at_ambient_and_elevated_temperatures SP - 359 PB - The Minerals, Metals & Materials Society (TMS) ER - TY - CHAP A1 - Altenberger, Igor A1 - Noster, Ulf A1 - Scholtes, Berthold A1 - Ritchie, Robert O. ED - Wagner, Lothar T1 - High Temperature Fatigue of Mechanically Surface Treated Materials T2 - Shot peening N2 - 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. Y1 - 2003 SN - 9783527606580 U6 - https://doi.org/10.1002/3527606580.ch62 SP - 483 EP - 489 PB - Wiley-VCH CY - Weinheim; [Cambridge] ER - TY - CHAP A1 - Juijerm, Patiphan A1 - Altenberger, Igor A1 - Noster, Ulf A1 - Scholtes, Berthold T1 - Residual stress relaxation and cyclic deformation behavior of deep rolled AlMg4.5Mn (AA5083) at elevated temperatures T2 - Materials Science Forum N2 - The cyclic deformation behavior of deep rolled and polished aluminium wrought alloy AlMg4,5Mn in the temperature range 20-300°C has been investigated. Results of quasistatic tension and compression tests of untreated specimens in the temperature range 20-300°C are presented. To characterize the fatigue behavior for stress-controlled tests as a function of test temperature, s-n curves, cyclic deformations curves and mean strains as a function of number of cycles are given. The residual stress- and work hardening states near the surface of deep rolled aluminium alloy AlMg4.5Mn before and after fatigue tests were investigated by X-ray diffraction methods. The investigated AlMn4.5Mn aluminium alloy shows cyclic hardening until fracture at all stress amplitudes in stress-controlled fatigue tests at 25-150°C. With increasing temperature the deformation behavior shifts from cyclic hardening to cyclic softening. Below a certain stress amplitude at a given temperature deep rolling led to a reduction of the plastic strain amplitude as compared to the untreated state through cyclically stable near-surface work hardening as indicated by stable FWHM-values. This reduction in plastic strain amplitude is associated with enhanced fatigue lives. The effectiveness of deep rolling is governed by the cyclic and thermal stability of near-surface work hardening rather than macroscopic compressive residual stresses. Since near-surface work hardening is known to retard crack initiation, deep rolling is also effective in temperature- and stress ranges where macroscopic compressive residual stresses have relaxed almost completely, but where near-surface work hardening prevails. Above certain stress amplitudes and temperatures, deep rolling has no beneficial effect on the fatigue behavior of AlMg4.5Mn. This is a consequence of instable near-surface microstructures, especially instable near-surface work hardening. KW - deep rolling KW - residual stress relaxation KW - high temperature fatigue Y1 - 2005 U6 - https://doi.org/10.4028/www.scientific.net/MSF.490-491.436 VL - 490-491 SP - 436 EP - 441 PB - Trans Tech Publications ER - TY - JOUR A1 - Anten, Kerstin A1 - Lebsanft, Markus A1 - Krauß, M. A1 - Noster, Ulf A1 - Scholtes, Berthold T1 - Einfluss von Randschichtzustand und Haltezeit auf die thermische Ermüdung der Magnesiumbasislegierung AZ31 JF - Materialwissenschaft und Werkstofftechnik N2 - Die vorliegende Arbeit befasst sich mit Untersuchungen zur thermischen Ermüdung der Magnesiumbasislegierung AZ31 im Temperaturbereich zwischen +50°C und +290°C. Die Experimente erfolgten unter konstanter Totaldeformation (out-of-phase-Beanspruchung) und es wurde der Verlauf der Spannungsamplitude sowie der plastischen Dehnungsamplitude über die Zahl der Temperaturzyklen ermittelt. Insbesondere wurde der Einfluss einer mechanischen Oberflächenbehandlung (Festwalzen) sowie von Haltezeiten auf den Verlauf der Schädigung untersucht. In beiden Fällen konnte kein signifikanter Unterschied zu unbehandelten Proben bzw. Beanspruchungen ohne Haltezeit festgestellt werden, welches auf die Wechselwirkungen zwischen Verformungs- und Rekristallisationsprozessen bei der thermischen Ermüdung zurückzuführen ist. T2 - Influence of near surface materials states and of hold-times on thermal fatigue of magnesium base alloy AZ31 Y1 - 2012 VL - 43 IS - 12 SP - 993 EP - 1000 PB - Wiley ER - TY - CHAP A1 - Nobre, J. P. A1 - Noster, Ulf A1 - Gibmeier, J. A1 - Altenberger, Igor A1 - Kornmeier, M. A1 - Dias, A. A1 - Scholtes, Berthold ED - Kainer, Karl U. T1 - Mechanical Behavior and Residual Stresses in AZ31 Wrought Magnesium Alloy Subjected to Four Point Bending T2 - Magnesium Alloys and Their Applications N2 - Several specimens of AZ31 magnesium alloy were taken in different directions from a rolled plate and subjected to tensile, compressive and four-point bending tests. Tensile and compressive tests allowed to characterize the mechanical properties of the material in the rolling and cross rolling directions. The bending tests were carried out in four different specimen types to take the effect of the anisotropy induced by the rolling procedure itself into account. Six strain gages per specimen allowed to observe the evolution of the strain with the bending moment during the tests. All bending specimens were bent until a total compressive deformation of 2.5 %. It was observed that the corresponding tensile strain was significant lower and slightly different for each specimen type. In addition, a characteristic non-uniform distribution of deformation twinning was observed. The induced residual stresses after bending were characterized by X-ray diffraction (XRD) and incremental hole-drilling (IHD). Due to the different mechanical behavior in tension and compression, an asymmetric residual stress distribution after bending could be observed. The neutral axis was, in all cases, shifted towards the tensile side. This observation agrees with the strain measurements during bending tests. Y1 - 2006 SN - 9783527607556 U6 - https://doi.org/10.1002/3527607552.ch53 SP - 336 EP - 341 PB - Wiley CY - Hoboken ER - TY - CHAP A1 - Altenberger, Igor A1 - Nalla, R. K. A1 - Noster, Ulf A1 - Liu, G. A1 - Scholtes, Berthold A1 - Ritchie, Robert O. ED - Lütjering, G. ED - Albrecht, J. T1 - Effects of Deep Rolling on the Fatigue Behavior of Ti-6Al-4V at Ambient and Elevated Temperatures T2 - Ti-2003 Science and Technology, Proceedings of the 10th World Conference on Titanium, held at the CCH-Congress Center Hamburg, Germany 13-18 July 2003, Vol 1 Y1 - 2003 UR - http://www.titaniumthemetal.org/epub/World-Conference-Proceedings-2003-Section-2/F7E2908C00CB5A5E8414934CBF8702B1/WTC%202003%20Sec%202.pdf SN - 3-527-30306-5 SP - 1059 EP - 1066 PB - Wiley ER - TY - JOUR A1 - Noster, Ulf A1 - Scholtes, Berthold T1 - Isothermal strain-controlled quasi-static and cyclic deformation behavior of magnesium wrought alloy AZ31 JF - International Journal of Materials Research / Zeitschrift für Metallkunde N2 - 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. Y1 - 2003 U6 - https://doi.org/10.1515/ijmr-2003-0098 VL - 94 IS - 5 SP - 559 EP - 563 ER - TY - CHAP A1 - Altenberger, Igor A1 - Noster, Ulf A1 - Nalla, R. K. A1 - Ritchie, Robert O. A1 - Scholtes, Berthold T1 - Residual stress relaxation in fatigue of mechanically surface treated materials T2 - Proceedings 132nd Annual TMS Meeting, March 2–6, 2003, San Diego, California Y1 - 2003 UR - https://www.researchgate.net/publication/273462779_Residual_stress_relaxation_in_fatigue_of_mechanically_surface_treated_materials SP - 312 ER -