In this article we will discuss about the plastic deformation of metals with its diagram. Referring to Fig. 6.2 the deformation of the specimen is elastic up to the yield point (or elastic limit) and it becomes plastic, i.e. the linear elastic region is followed by a nonlinear plastic region. Although yield strength is an important design parameter for machine [...]
All solids get deformed, i.e., show change in shape if an external load is applied on them. The basic types of deformations could be broadly divided into two categories: 1. Time-Independent Deformation: (i) The time independent deformation, which disappears (i.e., object returns to its original shape) on the release of load is called elastic deformation. Thus, elastic deformation is a [...]
In this article we will discuss about the atomic approach to elastic deformation of metals. At absolute zero, the two neighbouring atoms in a metal are in stable equilibrium state when the distance between them is r0. Fig. 6.11 illustrates this schematically. At large distance of separation between two atoms, the main force is of attractive nature, FA (negative). When [...]
Hot working is defined as the plastic deformation of a material at a temperature above its recrystallisation temperature, whereas working below this temperature is called cold working. The literal meaning of the words, hot and cold in ordinary sense does not apply here. For example, the working of lead and tin at room temperature is called hot working as their [...]
Plastic deformation occurs by the following modes: 1. Slip 2. Twinning 3. Kink. Mode # 1. Slip: The surface of a crystalline solid which has been polished, Fig. 6.14 (a) and then plastically deformed, generally gets covered with one or, more sets of parallel lines, Fig. 6.14 (c). At high magnifications, these 'slip lines' are found to be steps on [...]
In this article we will discus about:- 1. Introduction to Polycrystal 2. Dislocation Motion in Polycrystals 3. Ductility. Introduction to Polycrystal: The study of the basic mechanisms of the plastic deformations is facilitated by the study of plastic behaviour of single crystals. Most of the engineering materials are, however, polycrystalline, which contain a large number of grains with varying orientations. [...]
When a single crystal is continued to be deformed in the plastic range beyond the yield point, the shear stress required to produce further deformation continues to increase. The increase in the stress required to continue the deformation because of the previous plastic deformation is called as strain-hardening, or work-hardening. As the dislocation density also increases simultaneously with strain (dislocation [...]
The main elasticity-based principle for design of components is that the working-stress must remain within the elastic range. The efficient use of materials makes the designer to keep the working-stress quite close to the yield stress but definitely below it. The stress commonly calculated (total load divided by the total cross-sectional area) is called the nominal-stress. But the actual working-stress [...]
The change in dimensions of forms of matter under the action of applied forces is called 'deformation'. It is caused either by the mechanical action of external forces or by various physical and physio-chemical processes. To form various metallic shapes the deformation of metals is necessary. The deformed or mechanically worked metals are much superior to cast metals from which [...]