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Difference between Plastic Modulus and Moment Of Inertia

Difference between Plastic Modulus and Moment Of Inertia

In mechanics, plasticity is the ability of a material to undergo local plastic deformation, that is, to change its shape, without rupture, in response to applied forces. The two common measures of plasticity are the elastic modulus and the moment of inertia. While both are important measures of how pliable a material is, they serve different purposes. The plastic modulus quantifies how much a material will deform under a given load, while the moment of inertia measures how much that deformation will resist being reversed.

What is Plastic Modulus?

Plastic modulus is a measure of the flexibility of a material. It is defined as the Stress required to produce a unit strain within the elastic (proportional) deformation range of the material. Plastic modulus can be thought of as a measure of how “stiff” a material is. The higher the plastic modulus, the stiffer the material. Plastic modulus is typically measured in pounds per square inch (psi).

What is the Moment Of Inertia?

The Moment Of Inertia, also known as the second moment of area, is a measure of an object’s resistance to change its rotation. It is dependent on the shape and size of the object, as well as the distribution of mass. Objects with a large moment of inertia tend to be more resistant to changes in their rotation, while those with a small moment of inertia are more easily affected. The moment of inertia can be calculated for any object, provided that the dimensions and mass distribution are known. It is a valuable tool for engineers and physicists alike, as it can help to predict the behaviour of objects under different conditions.

Difference between Plastic Modulus and Moment Of Inertia

The Plastic Modulus (EP) and the Moment of Inertia (I) are two ways of measuring the stiffness of a material. The Plastic Modulus is the ratio of the stress to the strain below the proportional limit, while the Moment of Inertia is a measure of a material’s resistance to bending.

  • In general, materials with a high Plastic Modulus are stiffer than those with a low Plastic Modulus. The Plastic Modulus is also influenced by the material’s density, while the Moment of Inertia is not.
  • The Plastic Modulus is an important property for materials that will be subjected to loads that exceed the proportional limit. For these applications, it is necessary to know how much stress can be applied before the material fails.
  • The Moment of Inertia, on the other hand, is important for applications where bending is a concern. This property dictates how much a material can deflect before it fails. Materials with a high Moment of Inertia are more resistant to bending than those with a low Moment of Inertia.


In conclusion, the plastic modulus is a measure of how much a material will deform or stretch when a force is applied, while the moment of inertia measures how resistant a material is to rotational forces. When selecting materials for your next project, be sure to consider both of these properties to ensure that your product functions as intended.

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