Definition - What does Tensile Stress mean?
Tensile stress is the resistance of an object to a force tending to tear it apart. It is calculated as the highest tension the object can endure without tearing, and is measured in Newtons/sq.mm, but was initially denoted as tons/sq. in.
Stress is defined as the force per unit area of a material:
Stress = Force / Cross sectional area
and is a measurement of the strength of a material. Therefore, tensile stress refers to a force that attempts to pull apart or stretch a material.
Many of the mechanical properties of a material can be determined from a tensile test. In a tensile test, a sample is strained at a constant rate and the stress needed to maintain this strain rate is measured. A tensile test can determine:
- Elastic modulus
- Ultimate tensile stress
- Fracture stress
- Modulus of toughness
- Modulus of resilience
Tensile stress is also known as normal stress or tension.
Corrosionpedia explains Tensile Stress
Tensile stress is the stress state caused by an applied load that tends to elongate the material in the axis of the applied load, or in other words, the stress caused by pulling the material. The strength of structures of equal cross-sectional area loaded in tension is independent of the shape of the cross section. Materials loaded in tension are susceptible to stress concentrations such as material defects or abrupt changes in geometry. However, materials exhibiting ductile behavior (most metals for example) can tolerate some defects, while brittle materials (such as ceramics) can fail well below their ultimate material strength.
Tensile stress is the stress state leading to expansion; that is, the tensile stress may be increased until the reach of tensile strength, namely the limit state of stress.
The formula for computing the tensile stress in a rod is:
Tensile Stress = Force / Area
Tensile stress causes stress corrosion cracking (SCC), which is the combined influence of tensile stress and a corrosive environment. The required tensile stresses may be in the form of directly applied stresses or in the form of residual stresses. The problem itself can be quite complex. The situation with buried pipelines is a good example of such complexity.
Stresses that cause environmental cracking arise from:
- Residual cold work
- Thermal treatment
- Externally applied during service
In order to be effective, these stresses must be tensile (as opposed to compressive).
One method of controlling stress corrosion is to eliminate stress, or at least reduce it below the threshold stress for SCC. Residual stresses can be relieved by stress-relief annealing, and this is widely used for carbon steels.