Stress - Types of Stress, Definition and Formula

Stress is a physical quantity that defines force per unit area applied to a material. Stress is a physical science and engineering, force per unit area within the material that arises from externally applied forces. The maximum stress of material can stand before it breaks is called the breaking stress or ultimate tensile stress. Tensile means the material is under Tension. The forces acting on the material are trying to stretch the body. When the elastic bodies to regain their initial shape is cause for an internal restoring force. If we trying to compute this restoring force that acts on per unit area of the misshapen body it will be termed as stress. When the forces acting on the body are trying to squash it is compression.

The formula below is used to calculate the stress:

Stress =force/ Cross-sectional area
σ= F/A
σ= Stress
F= Force in Newton (N)
A= cross-sectional area in m²
Units of Stress= N/m² or Pascals (Pa)

Types Of Stress:

There is various type of stress in physics but mainly it is categorized into three forms :

  • 1. Normal Stress

  • 2. Tangential Stress or Shearing Stress

  • 3. Hydraulic stress

  • Normal Stress:

    Stress that occurs when a member is loaded by an axial force is known as normal force. In other words, when, the stress applied is perpendicular to the body. The length of body volume of the object is changed stress will be at normal. It represents the symbol σ. SI unit of Normal stress is MPa. 
    The formula below is used to calculate the Normal Stress:

    Normal stress=Axial force/Cross-Sectional Area

         σ =P/A

    Normal stress will occur when an object is placed in tension or compression.

    Longitudinal Stress: 

    When the length of the body changes its length by normal stress that is applied is known as Longitudinal Stress.

    Longitudinal Stress = Deforming Force / Area of cross section  

    Longitudinal Stress= F/A

    Longitudinal Stress can be further categorized and divided into two shorts. Tensile Stress can be observed when a rod is stretched under Newton’s third law of motion. A rubber band being stretched out is a common example of tensile stress. The opposite of tension is compression When it will be acting on the rod that is pushed by opposite or equal forces at its ends. If you’ve ever squeezed a rubber ball in your hands, you were creating compressive stress.

    Bulk Stress or Volume Stress:

    Volume Stress is the stress in which the volume of body changes due to the stress. Normal stress on a body causes change in length or volume and tangential stress produces the change in the shape of the body is called volume stress. A body that is under the force of pressure p, when submerged in a liquid, the body confront the force that is perpendicular to the surface of the body. 
    Bulk Stress = Force /Area = Pressure

    Shearing Stress:

    Shearing Stress is a force applied tangentially over the surface area of the plane. When the forces being applied to the surface is parallel to it and the stress which is acting on the surface also plots a tangent. This kind of stress is known as Shearing Stress.
    Sharing Stress= Force/ Surface Area = F/A

    Tensile Stress: 

    The force per unit area is defined as Tensile Stress. If the stress is applied then the length of the body is increasing because of the force. Tensile stress is observed when a rod is stretched under motion’s third law. Rubber is a common example of tensile stress. It is the quantity associated with stretching. It is denoted by σ.

    Compression Stress:

    When we apply a tangential force on the body the shape and volume of the body are changed. When the compression stress has applied the length of the body is decreased. Compression stress is opposite to the Tensile Stress. If you’ve ever squeezed a pet’s squeak toy in your hand, you are creating the compression stress on the body.

    Tangential Stress:

    When we expressed as force per unit area that is normal stress and tangential stress respectively. When two equal and opposite deforming forces are applied parallel to the cross-sectional area of an object, there is relative displacement between the opposite faces of the body, and the restoring force per unit area developed due to the applied tangential force is known as tangential stress.

    Hydraulic Stress:

    Hydraulic stress is the measure of the internal force per unit area acting on the liquids. Hydraulic Stress is the restoring force per unit area when the force is applied by the fluid on the body. Stress is not physically the same as pressure, because in pressure external force per unit area is considered, but in stress, it is the internal force per unit area. In the case of liquids to the hydraulic stress is defined in the same way.

    Radial Stress:

    The radial stress is for thick walled-cylinder, which is equal and opposite to the gauge pressure on the inside surface and zero on the outside surface. The circumferential stress and longitudinal stress is larger than radial stress so radial stress is neglected.

    Stress is a physical quantity that defines the internal force. The stress is specifying as the force across a “small” boundary per unit area of that boundary. Stress is a fundamental quantity, like velocity, torque (energy).

    A one question strike in your mind which thing you can stress and which are not. You must have noticed that there are certain objects just like rubber you can stretch easily. In other words, we can explain it when a stretching force (Tensile Force) applied to any object. It will expand. For example, a rubber band can stretch easily. Tensile Force applied on rubber object. However, can you stretch an iron rod? The answer is no because the tensile force is not applied on the iron rod.

    There are some basic premises of continuum mechanics, stress is a macroscopic concept. The particles to think in its description and analysis should be just small sufficient to be work as homogeneous in creation and state, but still large appropriate to ignore quantum effects and the detailed motions of molecules. Like this the force between two particles is really the mean of a very large number of atomic forces between their molecules; and in the physical term like mass, velocity, and forces, it works through the bulk of three-dimensional bodies, are assumed to be smoothly dispensed over them.

    Let us discuss this via an example-Take to a rubber pipe and an iron rod, take another object in a square shape and the second object hangs on the rubber pipe and iron rod. Wait for some time then pull both objects in the first object you can see that the first object has Tensile Force and another object does not have Tensile Force.

    Stress analysis is a part of applied physics which veil the classification of the internal distribution of internal forces in solid objects.

     It is an important part of engineering to study and design of structures such as dams, structural frames, and tunnels, mechanical parts, under prescribed or expected loads. It is also essential in much other regimentation; for example, in geology, to study theory like plate tectonics, volcanism and avalanches; and in biology, to understand the anatomy of living beings.