What is Elastic Material?
When an elastic material is deformed by an external force, the deformation is internally resisted and returns to its initial state once the external force is eliminated.
A stress-strain curve, which depicts the relationship between stress (the average restorative internal force per unit area) and strain, is used to characterise the elasticity of materials (the relative deformation). The curve is often nonlinear, but for sufficiently minor deformations, it can be represented as linear. Let us now discuss the properties, types and tests of elastic materials.
Properties of Elastic Material
Elastic materials are always inversely proportional to the strain of the material. In which the material remains the same before and after removing the externally applied load. Elastic material having a limit of loading is known as the elastic limit.
Up to the elastic limit, the range of loading is directly proportional to the strain rate. This range of curvature is a straight line and passes through the origin. This straight-line length depends on the properties of elastic material; it's known as the limit of proportionality.
Types of Elastic Material
Elastic materials vary with loading or unloading conditions. In these conditions, the material behaves on the basis of loading intensities as instant or sudden loading or gradual loading. Generally, we consider linear elastic material or nonlinear elastic material.
- Linear Elastic Material - This type of material is applied under load and shows a linear graph between stress and strain passing through the origin. Structural steel is taken as a linear elastic material that we use in the limit state design method.
- Non-Linear Elastic Material - This type of material is applied under load and shows a nonlinear graph between stress and strain passing through the origin. The non-linear elastic material is the scalar function of the deformation parameter. The non-linear elastic material is an artificial material also known as a hyper-elastic material.
For example, we consider rubber as a non-elastic material, and its slope (ds/de) is approximately parabolic, passing through the origin known as tangent modulus.
Test of Elastic Material
Elastic material test under a uniform tensile machine. In this machine, when a sample of steel bar is placed between the anchor and applies controlled tensile force, a certain point of pull is reversed, material regains its original shape; this phenomenon can be recorded on paper as a stress-strain curve. This test is also known as the stress-strain test. In the curve below, O to B is the elastic region.
Elastic material value can be termed as modulus of elasticity. This is represented by E. This modulus of elasticity is directly proportional to stress and inversely proportional to strain. From this test, we can get the modulus of elasticity of different materials as.
- Mild steel modulus of elasticity = 210 GPa
- Mild steel modulus of copper = 120 GPa
- Mild steel modulus of cast iron = 130 GPa
- Mild steel modulus of concrete = 17 GPa
- Mild steel modulus of plastic = 2 GPa
- Mild steel modulus of glass = 50-90 GPa
- Mild steel modulus of rubber = 0.02 GPa
Here we conclude that mild steel is more elastic than rubber and plastic material.
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