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Erhard Hornbogen

Bio: Erhard Hornbogen is an academic researcher from Ruhr University Bochum. The author has contributed to research in topics: Austenite & Martensite. The author has an hindex of 23, co-authored 172 publications receiving 2766 citations.


Papers
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Journal ArticleDOI
TL;DR: In this paper, structural and functional fatigue of NiTi shape memory alloys is investigated and four cases of fatigue are discussed: (1) the evolution of the stress-strain hysteresis in low cycle pull-pull fatigue of pseudo-elastic NiTi wires.
Abstract: Cyclic loading is one of the generic characteristic features of many of the present and potential future applications of NiTi shape memory alloys, no matter whether they exploit mechanical (pseudo-elasticity) or thermal shape memory (one and two way effect). Cyclic loading may well be associated with structural and functional fatigue, which both limit the service life of shape memory components. By “structural fatigue” we mean the microstructural damage that accumulates during cyclic loading and eventually leads to fatigue failure. There is a need to understand how microstructures can be optimized to provide good fatigue resistance. The term “functional fatigue” indicates that shape memory effects like the working displacement in a one way effect (1WE) actuator or the dissipated energy in a loading–unloading cycle of a pseudo-elastic (PE) damping application decrease with increasing cycle numbers. This is also due to a gradual change in microstructure. In both cases it is important to know how fatigue cycling affects shape memory properties. The present paper considers structural and functional fatigue of NiTi shape memory alloys. It discusses four cases of fatigue in NiTi shape memory alloys: (1) The evolution of the stress–strain hysteresis in low cycle pull–pull fatigue of pseudo-elastic NiTi wires. (2) Bending–rotation fatigue rupture of pseudo-elastic NiTi wires. (3) Strain localization during the stress induced formation of martensite. (4) Generic features of functional fatigue in NiTi shape memory actuator springs. The paper shows that fatigue of shape memory alloys is a fascinating research field and highlights the need for further work in this area.

661 citations

Journal ArticleDOI
TL;DR: In this paper, an underaged, aged, and overaged microstructure of an austenitic Fe-36 at.% Ni-12 at.%. Al alloy was investigated for fatigue crack propagation.

175 citations

Journal ArticleDOI
TL;DR: In this article, a survey of shape memory alloys (SMA) fatigue phenomena is presented, including classical mechanical fatigue (accumulation of defects, formation and growth of cracks, change of transformation temperatures, reduction or loss of memory, loss of pseudo elasticity or damping capacity).
Abstract: Shape memory alloys (SMA) produce the largest anomalous reversible strains of all crystalline materials: eSM < 10% in comparison to eFM < 1.0% and eFE < 0.1% (FM magnetostrictive, FE electrostrictive). They are considered as active materials for applications in which large scale motions are required or because of their high damping capacity for mechanical vibrations. Their use is however limited if a large number of cycles is applied. A survey is given on fatigue phenomena in SMA: 1. classical mechanical fatigue—accumulation of defects, formation and growth of cracks, 2. shape memory fatigue—change of transformation temperatures, reduction or loss of memory, loss of pseudo elasticity or damping capacity. Finally, it is shown how a modification of microstructure by thermo-mechanical treatments (TMT) affects fatigue resistance. In this context primary defects (as introduced by TMT) and secondary defects (introduced by mechanical or thermal cycling) have to be distinguished. In case of training for the two-way effect secondary defects are introduced voluntarily.

142 citations

Journal ArticleDOI
TL;DR: In this paper, a formulation for the factors which have an effect on the start of martensite was proposed, and they should be subdivided depending on whether they affect the equilibrium temperature To (Ms

131 citations

Journal ArticleDOI
TL;DR: In this article, a systematic description of cellular reactions with special account to the discontinuous precipitation is given, including the constitutional, nucleation, and other conditions for its occurrence; the role of grain boundaries, dislocations, and vacancies for the mechanism; the effect of continuous precipitation before discontinuous rainfall; multiple discontinuous reactions; effects of grain boundary structure, third elements, and external stress; reactions in highly defect crystals and amorphous solids.
Abstract: A systematic description is given of cellular reactions with special account to the discontinuous precipitation. The following special aspects of this reaction are discussed: The constitutional, nucleation, and other conditions for its occurrence; the role of grain boundaries, dislocations, and vacancies for the mechanism; the effect of continuous precipitation before discontinuous precipitation; multiple discontinuous reactions; effects of grain boundary structure, third elements, and external stress; reactions in highly defect crystals and amorphous solids. It is shown that all phenomena can be understood either by effects on driving force or mobility of the reaction front.

113 citations


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Book
30 Mar 2007
TL;DR: Friction stir welding (FSW) is a relatively new solid-state joining process that is used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding as discussed by the authors.
Abstract: Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.

4,750 citations

Journal ArticleDOI
TL;DR: In this article, a selfconsistent and logical account of key issues on Ti-Ni-based alloys from physical metallurgy viewpoint on an up-to-date basis is presented.

3,484 citations

Journal ArticleDOI
TL;DR: Shape memory alloys (SMAs) are a class of shape memory materials (SMMs) which have the ability to "memorise" or retain their previous form when subjected to certain stimulus such as thermomechanical or magnetic variations.

2,818 citations

Journal ArticleDOI
TL;DR: The current understanding of the fundamentals of recrystallization is summarized in this paper, which includes understanding the as-deformed state, nucleation and growth, the development of misorientation during deformation, continuous, dynamic, and geometric dynamic recystallization, particle effects, and texture.
Abstract: The current understanding of the fundamentals of recrystallization is summarized. This includes understanding the as-deformed state. Several aspects of recrystallization are described: nucleation and growth, the development of misorientation during deformation, continuous, dynamic, and geometric dynamic recrystallization, particle effects, and texture. This article is authored by the leading experts in these areas. The subjects are discussed individually and recommendations for further study are listed in the final section.

1,797 citations

Journal ArticleDOI
TL;DR: In this paper, the evolution of the new microstructures produced by two types of dynamic recrystallization is reviewed, including those brought about by severe plastic deformation (SPD).

1,777 citations