Force and Pressure

Tensile Stress

Tensile stress is a physical quantity related to tensile forces and stretching actions. It causes the elongation of any material along the axis of the load applied to the material. It is a state in which the load applied to an object tends to pull or stretch the material along the line of application of the force. The amount of direct load associated with the tensile loads leading to the stretching of an object is known as tensile stress. This tensile strength of structures that have equal cross-sectional areas put in the action of tension is solely independent of the shape of the cross-section of the material.

Tensile Stress

Tensile Stress

Definition of Tensile Stress

The resistance of an object against a force tending to tear it apart is tensile stress. The highest tension endured by the object in reference without resulting in tearing helps in the calculation of tensile stress. It is measured in different units. One of the main units being Newton/mm2. Tensile stress measures the strength of a material. Thus, it is related to a force that attempts to stretch or pull apart a specific material.

A tensile test is useful for measuring many mechanical properties of a body. Normal stress or just tension are some other names for tensile stress. The object returns to its original size and shape partially or completely when the applied stress is less than the tensile strength of the material. The material already begins to flow plastically when the stress starts approaching the value of the tensile strength. It rapidly forms a neck which is a constricted region. This is the point of the fracture.

The process of corrosion is accelerated by the tensile stress. It leads to the cracking of steel due to the intergranular corrosion induced by the stress. The mechanical properties and the overall strength of the corroded steel are reduced by tensile stress.

Mathematical Expression

The strain of the material is accelerated by the application of stress concentrations at the locations of defects of the material. It is also subjected to abrupt changes in geometry due to the tension present in it. Some materials have the ability to tolerate a certain number of defects before failure and show ductile behaviour. Some other materials which are brittle in nature may fail below their material strength. This stress is a state which leads to expansion. The tensile stress increases up to the limit state of stress which is the limit of tensile strength limit. This tensile stress is defined as the force associated with the stretching per unit area. The symbol \(\sigma\) denotes the tensile stress. The expression of tensile stress is:

\(\sigma = \frac{F}{A}\)

Tensile Properties

When a material is subjected to tensile stress, the material shows the following tensile properties:

  • Ultimate tensile strength (UTS): The value of the maximum stress which can be subjected to the material on the application of a force is called the Ultimate tensile strength.
  • Resilience modulus: This quantity is the ratio of the tensile stress and the double of the material’s Young’s modulus.
  • Elastic modulus: The stiffness of a material is expressed through its elastic modulus or the modulus of elasticity. This modulus is the ratio of the stress and the tensile strain in the cases of completely elastic deformation of the material. The stress-strain curve is very helpful in the calculation of the modulus of elasticity.
  • Fracture stress: The maximum stress experienced by the crack point of the material before the breaking down of that point is known as fracture stress. The denotation of this physical quantity is by the symbol \(\sigma _{f}\).

FAQs about Tensile Stress

Q.1. Define elastic limit.

Answer. The largest stress that can be applied to an object avoiding the permanent (plastic) deformation of the object is known as the elastic limit. If any material is subjected to stress at a point below its elastic limit, once the stress releases, it returns to its original size and shape. On the other hand, if the material is subjected to stress at a point exceeding its elastic limit, the permanent yield begins. When the stress is released, the material does not return completely to its original length. The accurate determination of the elastic limit of a material is difficult by using a testing machine that is universal. Thus, it is generally useful for educational purposes.

Q.2. How do we test the materials for their tensile stress?

Answer. We take a small sample of the material with a fixed cross-sectional area. This sample is pulled by a tensometer applying a constant strain rate until the point at which the sample breaks. The tensile strength of some metals is related linearly with the indentation hardness of the sample of the material. This results in devising non-destructive methods of testing of bulk metals. The process becomes more economical due to this relation. Rockwell hardness testers are used for indentation hardness and then tensile strength is calculated.

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