Tensile stress (σ) is the resistance of an object to forces that would tear it apart. It is calculated with the highest tension the object in question is subjected to, without tearing, and is measured in Newtons/mm. But originally expressed in tons/inch tensile stress can be defined as the magnitude of force applied along an elastic rod, divided by the cross-sectional area of the rod in the direction perpendicular to the applied force. Stretch means that the material is under tension and a force is acting on it trying to stretch the material.
Stress is the force per unit area of the material, so:
Tensile Stress = Force/Cross Sectional Area
Tensile stress measures the strength of a material; therefore, it refers to the force that attempts to pull apart or stretch a material. Many mechanical properties of materials can be determined by tensile testing.
Tensile stress may also be referred to as normal stress or tension. When the applied stress is less than the tensile strength of the material, the material will fully or partially return to its original shape and size. When the stress approaches the tensile strength value, the material has begun to flow plastically and rapidly develops a constricted region called the neck, which is the point at which it breaks.
Tensile stress accelerates the corrosion process and leads to intergranular corrosion and corrosion cracking of steel caused by intergranular stress. Thus, the stress reduces the mechanical properties and overall strength of the corroded steel.
Tensile stress is the state in which an applied load tends to stretch the material in the axis of the applied load, or in other words, it is the stress induced by pulling the material. Tensile stress is the amount of direct loading related to tensile force or tensile force responsible for the stretching of a material in the axis of the applied load. The strength of a structure with equal cross-sectional areas and loaded in tension is independent of the shape of the cross-section.
Materials loaded with tension are subject to stress concentrations and sudden changes in geometry at material defect locations, thereby accelerating the strain of the material. Some materials may exhibit ductility and can tolerate a certain number of defects before failing, while brittle materials may fail below their total material strength.
Tensile stress is the state of stress that causes expansion. Tensile stress may increase up to the limit of tensile strength, which is known as the limit state of stress and is defined as the force per unit area associated with stretching. It is represented by the symbol σ.
The formula for calculating the tensile stress in a rod is:
Tensile Stress = F/A
Tensile stress can lead to stress corrosion cracking (SCC), which is the combined effect of tensile stress and a corrosive environment. The desired tensile stress can be in the form of directly applied stress or residual stress.
Stresses that lead to environmental cracking can be caused by the following actions:
residual cold work
welding
grinding
heat treatment
Applied externally during service
To be effective, these stresses need to be tensile (rather than compressive).
One way to control stress corrosion is to relieve the stress, or at least reduce it below the threshold stress for stress corrosion cracking. Residual stresses can be removed by stress relieving annealing, which is widely used for carbon steels.
