Deformation is a process in which, under the influence of the loads applied to the body, its size and shape change. The change process can be of two types. The first is reversible (elastic), the second is residual (plastic) deformation.
The first type is a process in which, after eliminating the load, the body comes into its original form. In this case, the distance between atoms within the parameters of the crystal lattice changes.
Plastic deformation is a process in which the body does not restore its original shape after eliminating the load. Such a change is accompanied by a significant displacement of the parts of the crystal with respect to each other by a distance exceeding the distance in the crystal lattice between the atoms.
Plastic deformation always follows elastic. As a result, the total change at the moment of load exposure includes two processes - reversible and residual.
The deformation of metals is of great practical importance. This is primarily due to the fact that the processing of the material by pressure is based on the processes of changing the shape and size of the workpieces. At the same time, the emerging internal stress influences the physicochemical and mechanical properties of the material.
Plastic deformation of metals (its nature and size) depends on the plasticity of materials. This property can be evaluated in the process of relative narrowing or elongation of the samples during tensile testing. The ductility characteristics of metals also include an impact strength index . This property shows the work of destruction in the process of bending the notched sample with respect to the cross-sectional area of the notch.
The ductility of the material increases with increasing difference between yield strength and strength. Plastic deformation in brittle materials practically does not occur. Due to the fact that their yield strength is close to the level of tensile strength, they are destroyed quite quickly. This happens, for example, with glass, porcelain, cast iron, rocks. Meanwhile, heating the metal to a high temperature leads to the fact that the index of tensile strength practically coincides with the value of yield strength.
The residual change in the material of the polycrystalline structure has some features in comparison with the same process for a single-crystal body. Cold plastic deformation consists of a change in the shape and size of individual grains and a change in border volumes. Despite the fact that individual grains are subjected to deformation by twinning and sliding, their mutual connection and multiplicity in a polycrystalline body introduce some features into the process.
Due to the fact that the slip planes are oriented in space arbitrarily, the process itself will occur in different ways. Those grains whose slip planes are subjected to maximum tangential stresses begin to deform first. At the same time, nearby elements will be gradually involved in the process. Deformation changes their shape - they become elongated in the direction of the metal flow of the highest intensity (along, relative to the direction of deformation).
Thus, the material acquires a fibrous structure. Elongated non-metallic inclusions cause a difference in the properties of the fibers across and along. A change in the shape of the grains is accompanied by a change in the orientation of the crystal lattices in space. After most of the elements have the same orientation, a warp texture will form.