# Physical reason behind Plane Stress

• FAlonso
In summary, the concept of plane stress involves changing the perspective of viewing stress by rotating the view, which results in a change in stress values. This is due to the nature of Mohr's circle, where different angles on the circle represent different stresses. In real-life scenarios, this can be seen when pulling steel on a tensile machine, as it will shear at a maximum angle of 45 degrees. This is a result of the material's inherent properties and the way forces act on it.

#### FAlonso

I can now although do the maths related to plane stress etc but I have struggled to grasp the logic behind this concept. It says changing the way you see the stress by rotating the view, stress changes. My question is why ? Why is this so that we see stress with one value when standing at let's say 0 degrees with the axis of pipe under stress and different when we see it from 45 degrees rotated ? Is it some inherent material property or the force isn't really acting the way as we think and show in free body diagrams ? Can someone put it up simple ?

It's a function of mohrs circle. Plot the mohrs circle.you will see at different angles on the circle there is different stresses. In a real scenario if you put.steel in a tensile machine and pull it , it will shear at 45 degrees, this is because its maximum shear angle is 45 degrees

## What is plane stress?

Plane stress is a state of stress in which the stress components acting on a material are restricted to a single plane, while the stress components acting perpendicular to this plane are assumed to be zero. This is often seen in thin structures, such as plates or sheets.

## What is the physical reason behind plane stress?

The physical reason behind plane stress is the assumption that the thickness of a thin structure is much smaller than its other dimensions. This allows for the simplification of stress analysis, as the stress components in the direction perpendicular to the plane can be neglected.

## How is plane stress different from plane strain?

Plane stress and plane strain are two different states of stress in a material. Plane stress occurs when the stress components acting perpendicular to a plane are assumed to be zero, while plane strain occurs when the strain components perpendicular to a plane are assumed to be zero. In other words, plane stress is a case of two-dimensional stress, while plane strain is a case of two-dimensional strain.

## What are some common applications of plane stress analysis?

Plane stress analysis is commonly used in the design and analysis of thin structures, such as plates, shells, and beams. It is also used in the aerospace industry for the design of aircraft wings and fuselages, as well as in the automotive industry for the design of car bodies.

## How is plane stress analyzed in practice?

Plane stress analysis is typically done using the principles of solid mechanics, such as equations of equilibrium and compatibility, along with constitutive equations that relate stress and strain. Finite element analysis is also commonly used for more complex structures. In addition, experimental techniques, such as photoelasticity, can be used to visualize and analyze plane stress in a material.