Book contents
- Frontmatter
- Contents
- Preface
- 1 Mechanical background
- 2 The agents of deformation: lattice defects
- 3 Phenomenological and thermodynamical analysis of quasi-steady-state creep
- 4 Dislocation creep models
- 5 The effect of hydrostatic pressure on deformation
- 6 Creep polygonization and dynamic recrystallization
- 7 Diffusion creep, grain-boundary sliding and superplasticity
- 8 Transformation plasticity
- 9 Scaling and classification
- References
- Materials index
- Subject index
1 - Mechanical background
Published online by Cambridge University Press: 06 October 2009
- Frontmatter
- Contents
- Preface
- 1 Mechanical background
- 2 The agents of deformation: lattice defects
- 3 Phenomenological and thermodynamical analysis of quasi-steady-state creep
- 4 Dislocation creep models
- 5 The effect of hydrostatic pressure on deformation
- 6 Creep polygonization and dynamic recrystallization
- 7 Diffusion creep, grain-boundary sliding and superplasticity
- 8 Transformation plasticity
- 9 Scaling and classification
- References
- Materials index
- Subject index
Summary
To understand the physics of high-temperature deformation of crystals, we first need to describe the rheological behaviour of the solid in terms of mechanical and physical variables (stress, strain, temperature, pressure …). The description is embodied in constitutive equations, obtained by means of mechanical tests. In the present chapter, we summarily introduce the fundamental notions needed: stress, strain, and the various rheological constitutive equations. At high temperatures many materials flow viscously and viscous behaviour is therefore especially important. The principal methods of mechanical testing – creep at constant stress, deformation at constant strain-rate and stress relaxation – are presented and compared. The role of the variables in the constitutive equation is discussed: time, a special kinematic variable, explicitly appearing in transient creep only; strain, usually not a good variable, except when it coincides with the structural variables; strain-rate and stress. Minimum creep-rate, steady-state creep-rate and constant-structure creep-rate generally correspond to different conditions and must not be confused. We are concerned here with uniform deformation, but it may be useful to consider briefly the criteria for non-uniformity (i.e. localization) of deformation. Shear localization is a plastic instability manifesting itself as a stress drop on stress–strain curves.
Definitions
Stress and strain
To investigate the physics of the deformation processes in crystals it is first necessary to obtain a description of the phenomenon in terms of the relevant variables.
- Type
- Chapter
- Information
- Creep of CrystalsHigh-Temperature Deformation Processes in Metals, Ceramics and Minerals, pp. 1 - 37Publisher: Cambridge University PressPrint publication year: 1985