Technology & Engineering
Material Deformation
Material deformation refers to the change in shape or size of a material due to the application of force or stress. This process can occur through various mechanisms such as stretching, bending, or compressing. Understanding material deformation is crucial in engineering and manufacturing processes to ensure the structural integrity and performance of materials in various applications.
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6 Key excerpts on "Material Deformation"
eBook - PDFRod and Bar Rolling
Theory and Applications
- Youngseog Lee(Author)
- 2004(Publication Date)
- CRC Press(Publisher)
If the properties are dependent on the point, it is called inhomogeneous (or heterogeneous). 36 Chapter З 3.3 DEFORMATION MECHANISM When an external force is applied to material, its shape and size are changed. The response of a material subjected to an external load involves not only the visible shape and size but also shape and size at the atomic level in the interior of the material. This mechanism is called deformation. From the microscopic viewpoint, deformation is only possible because the lattices are not perfect, i.e., they have defects. There are many types of defects in the interior of a material. Zero-dimensional defects (point defects) such as vacancies and foreign atoms have no macroscopic extension into any direction but only atomic dimensions. Meanwhile one-dimensional defects that have a macroscopic extension in one direction are called dislocations. Grain boundaries are mostly well-known two- dimensional defects, and they can determine the crack path of a metal in a forced rupture. During deformation, a material response might be elastic as well as plastic. Elastic deformation results in dis placing the atoms in a lattice, but the displaced atoms move back to their original positions if the external force is unloaded. Plastic deformation occurs if the displaced atoms do not come back to their initial positions. These displaced atoms lead into elastic strain or plastic strain. There are two basic mechanisms that result in the plastic deformation of metals. The first one is gliding dislocation, where plastic deformation of a metal occurs by slipping of atoms on specific planes of a crystal. Figure 3-2 shows the two-dimensional atomic structure of an edge dislocation. Under the presence of a shear stress, this dislocation tends to migrate, as shown in the series of sketches, until there has been a displacement of the upper part of the crystal relative to the lower one by approximately one atom spacing.
- Eduard Starovoitov, Faig Bakhman Ogli Naghiyev(Authors)
- 2012(Publication Date)
- Apple Academic Press(Publisher)
Chapter 8 Foundations of the Theory of Plasticity Deformability of solids under the effect of external forces and their capability of per-ceiving constant or residual ( plastic ) strains at unloading is called plasticity . There is, however, no unequivocal dependence between stresses and strains arising in the body, which means that it is impossible to find strains in terms of stresses, and vice versa, one cannot determine stresses proceeding from known strains. The theory of plasticity deals with the laws interrelating stresses with elastoplastic deformations and the development of problem-solving methods on equilibrium and motion of deformed solid bodies. The theory of plasticity, forms the basis of today’s calculations of different structures, forging processes, rolling, punching, and so forth, as well as natural processes (e.g., orogenesis). This allows to reveal strength and de-formation potential of materials. Plastic deformation till fracture may reach 10–20%, while elastic deformations––only 0.3–0.5%. That is why strength calculations based on the assumption of only elastic deformations are often inexpedient both technically and economically. By taking plastic deformations into account, we may reduce stress concentration in structures, increase resistance of bodies to impact loads, de fi ne safety margins, rigidity and stability, ensuring thereby most ef fi cient functioning, reliability and safety of structures. PLASTICITY OF MATERIALS AT TENSION AND COMPRESSION The phenomena of elasticity and plasticity are displayed at sufficiently slow so-called static or quasi-static application of external forces. In this case, the phenomenon of deformability does not in fact depend on time, loading rate, and duration of external forces. Let us consider the basic phenomena of plasticity by a simplest example of tension and compression of a cylindrical sample.
eBook - PDF- J. Beddoes, M. Bibby(Authors)
- 1999(Publication Date)
- Butterworth-Heinemann(Publisher)
Stress and strain during deformation The ingot and continuous casting operations, outlined in the previous chapter, rarely yield a finished product that does not need further processing. Typically, ingots or strands are further processed by one of several bulk deformation operations, often followed by additional shaping via sheet deformation, machining or joining. The prin- ciples that underlie all of these processes are presented in Chapters 4-8. However, to analyse deformation processes, an understanding of the relationships between stress, strain and deformation is necessary. These relationships are presented in this chapter. During metal deformation, large changes in part geometry may occur. It is often important to understand the consequences of the geometrical shape change on the internal structure of the metal. Externally, force and power are applied to deform the part. Internally, the part reacts based on its microstructure and properties. These internal and external effects can usually be quantified to some degree by calcu- lations involving the stress-strain relationships of the workpiece. In this chapter basic stress-strain concepts are briefly introduced to illustrate their usefulness for metal deformation problems. The response of a material to mechanical loads is often measured by a uniaxial tension test. A tensile specimen, such as shown in Fig. 3.1, is loaded with a force, F. The exten- sion of the sample, typically measured by a change in gauge length, is recorded and the results displayed as a load-extension curve. Load-extension curves characteristic of low carbon steel and many nonferrous metals are shown in Fig. 3.1. Since both load and extension are clearly dependent on specimen size, they are not unique mate- rial properties. Consequently, tensile test results are almost always expressed as stress and strain. Engineering stress is defined as F (3.1) O'a = A-~ where: t7 a is the engineering stress
eBook - PDFThe World of Nano-Biomechanics
Mechanical Imaging and Measurement by Atomic Force Microscopy
- Atsushi Ikai(Author)
- 2007(Publication Date)
- Elsevier Science(Publisher)
C H A P T E R T W O Introduction to Basic Mechanics Contents 2.1 Elastic and Plastic Deformation of Materials 23 2.2 Stress and Strain Relationship 24 2.3 Mechanical Breakdown of Materials 27 2.4 Viscoelasticity 27 2.5 Mechanical Moduli of Biological Materials 29 2.5.1 Mechanical deformations 29 2.5.2 Shear deformation and rigidity modulus 30 2.5.3 Triaxial deformation and bulk compressibility 30 2.5.4 Y , G , and K are all related through Poisson’s ratio 31 2.5.5 What is Poisson’s ratio? 34 2.6 Fluid and Viscosity 35 2.7 Adhesion and Friction 36 2.8 Mechanically Controlled Systems 38 Bibliography 41 2.1 Elastic and Plastic Deformation of Materials Structural samples (often called members in engineering termi-nology) undergo deformations when a tensile, compressive, or shear force is applied. The tensile force elongates, compressive force shortens, and shear force distorts them. Upon removal of the applied force, the shape of an elastic sample returns to the original one, and, if not, the sample is partially or totally plastic. In many cases, samples show an elastic deformation while the applied force 23 24 Introduction to Basic Mechanics is small and as the force becomes greater, contribution of plastic deformation gradually increases. During an elastic deformation, the covalent and noncovalent bonds that hold the atoms in the sample body are not broken but displaced from their equilibrium distance, i.e. , deformed due to the application of an external force, but on removal of the force all the deformed bonds return to their equilibrium positions, recovering the original shape of the object. The proportionality constant of the stress–strain relationship in the elastic regime of deformation is called Young’s modulus. The general introduction to the mechanics of materials is given by Timoshenko [1] and an advanced version is presented in Ref. [2]. A concise treatise of the theory of mechanics is found in Ref.
eBook - PDF- R.J. Crawford(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER 2 - Mechanical Properties of Plastics - Deformation Introduction In Chapter 1 the general mechanical properties of plastics were introduced. In order to facilitate comparisons with the behaviour of other classes of materials the approach taken was to refer to standard methods of data presentation, such as stress-strain graphs, etc. However, it is important to note that when one becomes involved in engineering design with plastics, such graphs are of limited value. The reason is that they are the results of relatively short-term tests and so their use is restricted to quality control and, perhaps, the initial sorting of materials in terms of stiffness, strength etc. Designs based on, say, the modulus obtained from a short-term test would not predict accurately the long-term behaviour of plastics because they are viscoelastic materials. This viscoelasticity means that quantities such as modulus, strength, ductility and coefficient of friction are sensitive to straining rate, elapsed time, loading history, temperature, etc. The time-dependent change in the dimensions of a plastic article when subjected to a constant stress is called creep. As a result of this phenomenon the modulus of a plastic is not a constant, but provided its variation is known then the creep behaviour of plastics can be allowed for using accurate and well established design procedures. Metals also display time dependent properties at high temperatures so that designers of turbine blades, for example, have to allow for creep and guard against creep rupture. At room temperature the creep behaviour of metals is negligible and so design procedures are simpler in that the modulus may be regarded as a constant. In contrast, thermoplastics at room temperature behave in a similar fashion to metals at high temperatures so that design procedures for relatively ordinary load-bearing applications must always take into account the viscoelastic behaviour of plastics.
eBook - PDF- T. W. Clyne, J. E. Campbell(Authors)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
4 Mechanisms of Plastic Deformation in Metals The capacity of metals to undergo large plastic strains (without fracturing) is one of their most important characteristics. It allows them to be formed into complex shapes. It also means that a component under mechanical load is likely to experience some (local) plasticity, rather than starting to crack or exhibit other kinds of damage that could impair its function. Metals are in general superior to other types of material in this respect. This has been known for millennia, but the reasons behind it, and the mechanisms involved in metal plasticity, only started to become clear less than a century ago and have been understood in real depth for just a few decades. Central to this understanding is the atomic scale structure of dislocations, and the ways in which they can move so as to cause plastic deformation, although there are also several other plasticity mechanisms that can be activated under certain circumstances. These are described in this chapter, together with information about how they tend to be affected by the metal microstructure. This term encompasses a complex range of features, including crystal structure, grain size, texture, alloying additions, impurities, phase constitution etc. 4.1 Basic Dislocation Structures and Motions 4.1.1 The Atomic Scale Structure of Metals Dislocations can exist in various types of (crystalline) material, but they tend to be both more numerous and more mobile in metals, compared with, say, ceramics, intermetallics or organic materials. The underlying reason for this is related to the types of interatomic bonding in different materials. In non-metallic materials such as ceramics, there are strong directional bonds between neighboring atoms, usually either ionic (adjacent atoms carrying charge of opposite sign) or covalent (electrons local- ized in orbitals shared between neighboring atoms), or possibly there is an element of both types.
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