Pokluda / Šandera / Sandera Micromechanisms of Fracture and Fatigue

In a Multi-scale Context
1. Auflage 2010
ISBN: 978-1-84996-266-7
Verlag: Springer
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 293 Seiten, eBook

Reihe: Engineering Materials and Processes

Micromechanisms of Fracture and Fatigue forms the culmination of 20 years of research in the field of fatigue and fracture. It discusses a range of topics and comments on the state of the art for each.

The first part is devoted to models of deformation and fracture of perfect crystals. Using various atomistic methods, the theoretical strength of solids under simple and complex loading is calculated for a wide range of elements and compounds, and compared with experimental data. The connection between the onset of local plasticity in nanoindentation tests and the ideal shear strength is analysed using a multi-scale approach. Moreover, the nature of intrinsic brittleness or ductility of perfect crystal lattices is demonstrated by the coupling of atomistic and mesoscopic approaches, and compared with brittle/ductile behaviour of engineering materials.

The second part addresses extrinsic sources of fracture toughness of engineering materials, related to their microstructure and microstructurally-induced crack tortuosity. Micromechanisms of ductile fracture are also described, in relation to the fracture strain of materials. Results of multilevel modelling, including statistical aspects of microstructure, are used to explain remarkable phenomena discovered in experiments.

In the third part of the book, basic micromechanisms of fatigue cracks propagation under uniaxial and multiaxial loading are discussed on the basis of the unified mesoscopic model of crack tip shielding and closure, taking both microstructure and statistical effects into account. Applications to failure analysis are also outlined, and an attempt is made to distinguish intrinsic and extrinsic sources of materials resistance to fracture.

Micromechanisms of Fracture and Fatigue provides scientists, researchers and postgraduate students with not only a deep insight into basic micromechanisms of fracture behaviour of materials, but also a number of engineering applications.

Zielgruppe

Research

Autoren/Hrsg.

Pokluda, Jaroslav

Šandera, Pavel

Sandera, Pavel

Inhaltsverzeichnis

Deformation and Fracture of Perfect Crystals.- Brittle and Ductile Fracture.- Fatigue Fracture.- Final Reflections.

Leseproben

"Chapter 4 Final Reflections (p. 243-244)

The book has been ?nished and the authors would like to thank in particular those tolerant and patient readers who have read it to the very end. One can be quite sure that such readers would not mind further brief re?ection. In spite of the fact that these ?nal remarks will bring no additional scienti?c information, the authors believe that selected pieces of knowledge that are assembled in the main text might be worth mentioning again. Because this book preferentially refers to the scienti?c work of the authors, only the results that arose from their own research will be highlighted. On the other hand, many important things still remain open for further investigations. Some of these tasks related to our research will also be recalled.

4.1 Useful Results

1. The highest achievable tensile strength of a solid of a particular chemical composition, the ideal tensile strength of the perfect crystal, strongly depends on the stress triaxiality. For the majority of metallic crystals, the ideal strength related to the volumetric instability increases almost linearly with increasing transverse biaxial stresses. On the other hand, ceramic crystals with a diamond structure exhibit a sharp maximum either close to the zero biaxial stress (Si, Ge) or in the compressive biaxial region (C).

2. Under uniaxial tension, however, perfect metallic crystals usually fail when reaching the ?rst shear instability. Therefore, their uniaxial ideal strength siut does not exceed 10GPa which is far below their volumetric ideal uniaxial strength and only several times higher than that of the strongest related engineering metallic materials. This is not necessarily true for the case of isotropic (hydrostatic) tension in which the ideal strength siht usually reaches values as high as several tens of GPa.

3. The ranking of tensile strengths su of the strongest grades of engineering materials with chemically di?erent matrices nearly follows that of siht of related perfect crystals. The same is true for the ductile/brittle response of engineering materials and that of their perfect crystals. Therefore, these mechanical properties are, to a considerable extent, predetermined by those of a perfect lattice. On the other hand, such a correspondence is not apparent for the fracture strain and its dependence on the stress triaxiality. This property is determined instead by crystal defects and secondary phases.

4. Crystals of metals and diamond exhibit a nearly linear decrease in ideal shear strength with increasing superimposed isotropic (hydrostatic) stress sh. On the other hand, the dependence tis(sh) of covalent crystals Si, Ge and SiC reveals an opposite trend. These trends also refer to the dependence of ideal shear strength on the superimposed normal stress. This is in agreement with the normal stress in?uence found for the dislocation nucleation stress (non-Schmid behaviour). However, the ideal shear strength of Cu and Ni crystals becomes lowered by both tensile and compressive normal stresses."

Über Autor(innen)

Jaroslav Pokluda received his PhD in the Physics of Condensed Matter from the University of J. E. Purkyne, Brno, Czech Republic. He was with the Military Research Institute of Materials and Technology until 1985 and, since then, he has been with the Brno University of Technology as Associate Professor, Professor and Head of the Department of Materials Micromechanics and Applied Acoustics. His research interests include modelling micromechanisms of fracture and fatigue (metals and ceramics); atomistic computations of mechanical properties of crystals; quantitative fractography (metals and ceramics); and uniaxial and biaxial fatigue of materials (metals). He is an author or co-author of 3 textbooks and 92 papers in scientific journals. He has edited 4 special issues of scientific journals (Engineering Fracture Mechanics, Strength of Materials, Materials Science Forum) and is on the editorial board of the journals Strength of Materials and Physicochemical Mechanics of Materials. Since 1999 he has been the Czech representative in the European Structural Integrity Society (ESIS). He was a co-chair of 7 international conferences MSMF1-6, and ECF17. He received commemorative medals awarded by the Institute of Materials Research at the Slovak Academy of Sciences, Slovakia (2005) and Brno University of Technology, Czech Republic (2008). Pavel Šandera received his PhD in the Physics of Condensed Matter from the Brno University of Technology, Czech Republic. Since 1978 he has been with the Brno University of Technology as Associate Professor and Professor (2006). His research interests include modelling micromechanisms of fracture and fatigue (metals and ceramics); atomistic computations of mechanical properties of crystals; stochastic geometry; and fatigue of materials (metals). He has published 41 papers in scientific journals and edited specials issues of Materials Science Forum and Engineering Failure Analysis. He is on the editorial board ofthe Engineering Mechanics journal. He received the commemorative medal awarded by the Brno University of Technology, Czech Republic (2009).