Elastic materials strain instantaneously when stretched and just as quickly return to their original state once the stress is removed. Viscoelastic materials have elements of both of these properties and, as such, exhibit time dependent strain.
The deformation process can be divided into four main stages: elastic, plastic, yield, and fracture. During the elastic stage, the material deforms under stress but returns to its original shape once the stress is removed. In the plastic stage, the material undergoes permanent deformation due to the applied stress. The yield stage is the point at which the material begins to deform plastically, and the fracture stage occurs when the material breaks apart under extreme stress.
Several factors can influence the stages of deformation, including the type of material, the rate of deformation, and the temperature. Some materials may have a higher elastic limit, making them more resistant to deformation, while others may have a lower yield strength, making them more susceptible to plastic deformation. The rate of deformation can also impact the stages, as slower rates may allow the material to deform more elastically. Temperature can also play a role, as it can affect the strength and ductility of the material.
The stages of deformation can be measured through various techniques, such as tensile testing, compression testing, and shear testing. These methods involve applying controlled stress to a sample of the material and measuring its response. Tensile testing, for example, can determine the yield strength and fracture point of a material, while shear testing can measure its shear strength.
The elastic stage of deformation can be reversed, as the material returns to its original shape once the stress is removed. However, the plastic, yield, and fracture stages are irreversible. Once a material undergoes plastic deformation, it will not return to its original shape, and any further stress will result in more permanent deformation or fracture.
The stages of deformation are closely related to a material's properties, such as its strength, ductility, and toughness. A material with high strength and low ductility may have a shorter elastic stage and a quicker transition to plastic deformation. On the other hand, a material with lower strength and higher ductility may have a longer elastic stage and a slower transition to plastic deformation. The fracture stage is also affected by a material's toughness, which measures its ability to withstand stress before breaking.