can anyone explain the concept of modulus of elasticity?

Answer 1

The modulus of elasticity, or Young's Modulus (E), is the property of a material that relates strain (how much the material will stretch) to stress (how much force is applied, per unit cross section). Its units are the same as stress - psi (pounds per square inch) or Pa (Pascals, or Newtons per square meter). Stress divided by Young's modulus = strain. Strain is dimensionless - it's length of stretch per length of material.

As a simple example, if you take an aluminum (E= 10Mpsi) rod with a cross-section of 1 square inch, and apply a tensile force of 10,000 pounds, the rod will stretch 0.1% - (10,000 psi stress)/10,000,000 psi) = 0.001.

This modulus is only applicable up to the elastic limit of the material. That is the stress beyond which the material will permanently deform.

Answer 2

Most metals and ceramics, along with many other materials, are isotropic - their mechanical properties are the same in all directions, but metals and ceramics can be treated to create different grain sizes and orientations. This treatment makes them anisotropic, meaning that Young's modulus will change depending on which direction the force is applied from. However, some materials, particularly those which are composites of two or more ingredients have a "grain" or similar mechanical structure. As a result, these anisotropic materials have different mechanical properties when load is applied in different directions. For example, carbon fiber is much stiffer (higher Young's modulus) when loaded parallel to the fibers (along the grain). Other such materials include wood and reinforced concrete. Engineers can use this directional phenomonon to their advantage in creating various structures in our environment. Copper is an excellent conductor of electricity and is used to transmit electricity over long distance cables, however copper has a relatively low value for Young's modulus at 130 GPa and it tends to stretch in tension. When the copper cable is bound completely in steel wire around its outside this stretching can be prevented as the steel (with a higher value of Young's modulus in tension) takes up the tension that the copper would otherwise experience.

Answer 3

In lay tems you can think of modulus of elasticity, E, as stifness even though stiffness is actually a function of moment of inertia as well (E*I).

Think of steel or concrete as having a high E value, very stiff and plastic having a low E value, very flexible.