Book contents
- Frontmatter
- Contents
- Preface
- 1 Stress and Strain
- 2 Elasticity
- 3 Mechanical Testing
- 4 Strain Hardening of Metals
- 5 Plasticity Theory
- 6 Strain Rate and Temperature Dependence of Flow Stress
- 7 Slip and Crystallographic Textures
- 8 Dislocation Geometry and Energy
- 9 Dislocation Mechanics
- 10 Mechanical Twinning and Martenitic Shear
- 11 Hardening Mechanisms in Metals
- 12 Discontinuous and Inhomogeneous Deformation
- 13 Ductility and Fracture
- 14 Fracture Mechanics
- 15 Viscoelasticity
- 16 Creep and Stress Rupture
- 17 Fatigue
- 18 Residual Stresses
- 19 Ceramics and Glasses
- 20 Polymers
- 21 Composites
- 22 Mechanical Working
- APPENDIX I Miller Indices
- APPENDIX II Stereographic Representation of Orientations
- Index
15 - Viscoelasticity
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- 1 Stress and Strain
- 2 Elasticity
- 3 Mechanical Testing
- 4 Strain Hardening of Metals
- 5 Plasticity Theory
- 6 Strain Rate and Temperature Dependence of Flow Stress
- 7 Slip and Crystallographic Textures
- 8 Dislocation Geometry and Energy
- 9 Dislocation Mechanics
- 10 Mechanical Twinning and Martenitic Shear
- 11 Hardening Mechanisms in Metals
- 12 Discontinuous and Inhomogeneous Deformation
- 13 Ductility and Fracture
- 14 Fracture Mechanics
- 15 Viscoelasticity
- 16 Creep and Stress Rupture
- 17 Fatigue
- 18 Residual Stresses
- 19 Ceramics and Glasses
- 20 Polymers
- 21 Composites
- 22 Mechanical Working
- APPENDIX I Miller Indices
- APPENDIX II Stereographic Representation of Orientations
- Index
Summary
Introduction
In classic elasticity, there is no time delay between application of a force and the deformation that it causes. For many materials, however, there is additional timedependent deformation that is recoverable. This is called viscoelastic or anelastic deformation. When a load is applied to a material, there is an instantaneous elastic response, but the deformation also increases with time. This viscoelasticity should not be confused with creep (Chapter 16), which is time-dependent plastic deformation. Anelastic strains in metals and ceramics are usually so small that they are ignored. In many polymers, however, viscoelastic strains can be very significant.
Anelasticity is responsible for damping of vibrations. A high damping capacity is desirable where vibrations might interfere with the precision of instruments or machinery and for controlling unwanted noise. A low damping capacity is desirable in materials used for frequency standards, in bells, and in many musical instruments. Viscoelastic strains are often undesirable. They cause the sagging of wooden beams, denting of vinyl flooring by heavy furniture, and loss of dimensional stability in gauging equipment. The energy associated with damping is released as heat, which often causes an unwanted temperature increase. Study of damping peaks and how they are affected by processing has been useful in identifying mechanisms. The mathematical descriptions of viscoelasticity and damping are developed in the first part of this chapter. Then several damping mechanisms are described.
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- Chapter
- Information
- Mechanical Behavior of Materials , pp. 244 - 258Publisher: Cambridge University PressPrint publication year: 2009