# Stress, strain, pressure

• manimaran1605
But yes, that's what I meant. In summary, stress is defined as force per unit area, specifically the internal force between particles in a material per unit area. Pressure is considered a type of stress, specifically an isotropic part of the stress tensor. The bulk and shear modulus are used in finding the rheological behavior of gases and most liquids. The concept of internal force as a restoring force depends on the situation, and in general, stress is a tensor with different components depending on the orientation of the area through a point in the body.

#### manimaran1605

I studied that Stress is defined as Force per unit area. Force here referred to internal force between the particles in the materials per unit area. am i right?

Is pressure a kind of stress? (Internal force per unit volume) for fluids but i have studied that pressure is external force per unit volume

Give me some example what is the use of finding Bulk and Shear modulus

manimaran1605 said:
I studied that Stress is defined as Force per unit area. Force here referred to internal force between the particles in the materials per unit area. am i right?
Yes.
Is pressure a kind of stress? (Internal force per unit volume) for fluids but i have studied that pressure is external force per unit volume

Pressure is an isotropic part of the stress tensor.
Give me some example what is the use of finding Bulk and Shear modulus
Look up the general tensorial equation for a Newtonian fluid in a fluid mechanics book. This equation describes the rheological behavior of gases and most liquids.

1 person
Is that internal force is restoring force?If yes, Does that mean all internal forces are restoring forces?

This is just a matter of definition, surely. A force would only be described as a 'restoring force' if you were dealing with an equilibrium situation i.e. when there are no external applied forces or when your system consists of balancing stress and applied forces.

Pressure is not force per unit volume. It is force per unit AREA.

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1 person
yeah. and (I think) the stress IS the entire internal force per area at some given point. (i.e. not including 'body forces' like gravity). So it is quite general, and in a general case, it will not be a restoring force. But for an example, if you have a (linear) sound wave moving through some fluid, then I guess this is an example of when stress can be a restoring force.

edit: an example of when an internal force is not a restoring force: uh... let's say we have some fluid inside a closed cylinder, if we push one wall inward, there will be stresses inside the fluid, which propagate through the fluid (starting from the moving wall). These stresses act to change the system, so that it goes from lower density to higher density throughout the fluid.

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BruceW said:
yeah. and (I think) the stress IS the entire internal force per area at some given point.

In general (as chestermiller implied) stress is a tensor, described by 6 components (3 for direct stress and 3 for shear stress). These 6 components describe the "force per unit area" on an "area" that is in any orientation through a point in the body, and in general the force will be different depending on the orientation of the area. (I'm not sure if that's what you meant by the "entire internal force").

The idea of "stress = force per unit area" is often used as an explanation of the concept of stress for beginners, in simple situations like the tension in a string or rod, when 5 of the 6 stress components are zero, and the "area" is perpendicular to the non-zero stress component.

"Internal pressure" is the special case where the 3 direct stress components are equal, and the 3 shear components are all zero. In that case, the "force per unit area" is independent of the orientation of the "area" in the body.

AlephZero said:
These 6 components describe the "force per unit area" on an "area" that is in any orientation through a point in the body, and in general the force will be different depending on the orientation of the area. (I'm not sure if that's what you meant by the "entire internal force").
yeah, I didn't mention the tensor aspect, since I'm guessing the OP is not on to that stuff yet.

## What is the difference between stress, strain, and pressure?

Stress is the internal force that a material experiences when it is subjected to external forces. Strain is the resulting deformation or change in shape of the material due to the applied stress. Pressure, on the other hand, is the force applied per unit area, typically exerted by a fluid or gas on a surface.

## How do stress and strain affect the behavior of materials?

Stress and strain can cause a material to either deform permanently or return to its original shape after the external forces are removed. The amount and type of stress and strain a material experiences can also determine its strength, stiffness, and ductility.

## What factors can influence the amount of stress and strain a material experiences?

The amount of stress and strain a material experiences can be influenced by factors such as the type and amount of external forces applied, the material's properties (such as elasticity and yield strength), and the material's shape and size.

## What are the different types of stress and strain?

There are four main types of stress: tensile, compressive, shear, and torsional. Tensile stress is when a material is pulled apart, compressive stress is when a material is pushed together, shear stress is when a material is twisted, and torsional stress is when a material is bent. Similarly, there are four types of strain: normal, shear, volumetric, and linear. Normal strain occurs when a material is stretched or compressed, shear strain occurs when a material is twisted, volumetric strain occurs when a material's volume changes, and linear strain occurs when a material's length changes.

## How do engineers and scientists measure stress and strain?

Stress and strain can be measured using various techniques, such as strain gauges, extensometers, and load cells. These instruments can provide information about the amount and type of stress and strain a material experiences, as well as how it changes over time. In addition, mathematical equations and models can also be used to analyze and predict the behavior of materials under stress and strain.