Stress

Stress is defined as the force exerted on a material’s unit area in physics. Strain is the term for the effect of stress on the body. The body can be deformed as a result of stress. Stress units can be used to determine how much force a material has experienced. Depending on the direction of the deforming forces operating on the body, stress can be divided into three kinds. Let’s take a look at them one by one.

What is stress?

When a deforming force is applied to an item, it deforms. To return the item to its original shape and size, an opposing force will be generated inside it.

This restoring force will be of equal size as the applied deforming force, but in the opposite direction. Stress is the measurement of the material’s restoring force per unit area.

As a result, stress is defined as “the restoring force per unit area of the material.” Because it’s a tensor quantity, it’s also a tensor quantity. The Greek letter(σ) is used to represent it. Pa or N/m2 are the nits of measurement. Mathematically, it’s written as

σ=F/A

Where, 

• F = restoring force measured in newton or N

• A = area of cross section measured in m2 

• σ = stress measured using N/m2 or Pa.

Stress units 

Stress can be measured in a variety of ways. Stress units are listed in the table below.

Types of stress

In physics, there are various types of stress, Normal stress and tangential or shearing stress, on the other hand, are the two most common forms. The following sections discuss some of the various types of stress.

Normal stress: 

When the direction of the deforming force is perpendicular to the cross-sectional area of the body, stress is said to be normal stress. As the length of the wire or the volume of the body varies, the stress will be normal. Based on the force dimension, normal stress is further classified into two types

Longitudinal stress

Bulk stress or volumetric stress

Longitudinal stress:

Consider the shape of a cylinder. The stress experienced by the cylinder is called longitudinal stress when two cross-sectional sections of the cylinder are exposed to equal and opposite forces.

Deforming Force / Area of Cross-section = F/A = Longitudinal Stress

As the name implies, when the body is subjected to long-term stress-

The deforming force will act along the body’s whole length.

The length of the body changes as a result of longitudinal tension. As a result, there is a little difference in diameter.

The Longitudinal Stress stretches or compresses the thing along its whole length. As a result, based on the direction of deforming force, it can be further categorised into two types:

Tensile stress

Compressive stress

Tensile stress

Tensile stress is defined as a stress that occurs when a deforming force or applied force causes an increase in the length of an object. For example, a rod or wire can be stretched by drawing it at both ends with equal and opposite forces (outwards).

Compressive stress

When a deforming force or applied force causes an object’s length to shrink, the resulting tension is known as compressive stress. When a rod or wire is compressed/squeezed by pulling it inwards with equal and opposite forces at both ends, for example.

Bulk stress or volume stress

When a deforming force or applied force acts on an object in all dimensions, causing a change in volume, this is referred to as volumetric stress or bulk stress. When the volume of a body changes as a result of a deforming force, volume stress arises.

Shearing stress or tangential stress

Shearing stress or tangential stress occurs when the direction of the deforming force or external force is parallel to the cross-sectional area of the item. 

Stress causes and effects

Multiple physical reasons, including external forces and internal physical processes, can create stress in a material body. Some agents (such as gravity, temperature and phase changes, and electromagnetic fields) have an effect on the bulk of the material, Changing  with position and time. Other factors (such as external loads and friction, ambient pressure, and contact forces) can concentrate stresses and forces on certain surfaces, lines, or points, as well as on extremely short time intervals (as in the impulses due to collisions). Self-propulsion of microscopic particles causes macroscopic stress patterns in active matter. In general, a piecewise continuous function of space and time is used to express the stress distribution in a body.

Stress, on the other hand, is frequently associated with a variety of material effects, including changes in physical properties such as birefringence, polarisation, and permeability. Even if the strain (deformation) is too slight to be detected, the imposition of stress by an external agent causes some strain (deformation) in the material. Such strain in a solid material will cause an internal elastic stress, similar to the reaction force of a stretched spring, which will tend to restore the material to its original undeformed state. Fluid materials (liquids, gases, and plasmas) can only resist deformations that change their volume by definition. However, even with fluids, if the deformation changes over time, there will generally be some viscous tension opposing the change. These types of strains might be shear or typical in nature. The article on viscosity discusses the molecular origins of shear forces in fluids. Sharma has the same formula for normal viscous stresses (2019)

The relationship between stress and its consequences and causes, such as deformation and rate of deformation change, can be highly complex (although a linear approximation may be adequate in practice if the quantities are small). Stress that exceeds the material’s strength limitations causes irreversible deformation (plastic flow, fracture, cavitation) or even changes the crystal structure and chemical makeup of the materials.

Stress analysis

The determination of the internal distribution of internal forces in solid objects is the subject of stress analysis, which is a field of applied physics. It’s a crucial tool in engineering for studying and designing structures like tunnels, dams, mechanical parts, and structural frames that are subjected to prescribed or expected stresses. It’s also significant in a variety of other fields, such as geology, where it’s used to research plate tectonics, vulcanism, and avalanches, and biology, where it’s used to learn about the anatomy of living things.

Conclusion

In a nutshell, stress can be represented as –