Question

Explain elasticity, the limit of elasticity, yield point, and breaking point.

Answer 1

Hint: The force applied to an object per unit area is called stress. The effect produced by the stress is called strain. Strain can be defined as a relative change in the length of an object under stress. When a body is subjected to stress the behavior of the object can be described by the stress-strain relationship graph. Through this graph, we can explain the terms given in the question.

Complete Step By Step Answer:

The above diagram explains the stress-strain curve. This graph represents a material’s stress value against the strain value when the corresponding material is subjected to an external force. The Y-axis represents strain and the X-axis represents the stress of the material.
From the above curve, we can see from $ 0 $ point E the line is straight expressing the linear relationship between the stress and the strain. Therefore this region corresponds to Hooke’s law. Hooke’s law says that within the material’s elastic limit the material’s strain is directly proportional to the stress applied on it. If a body exhibits an elastic behavior then this body will not allow permanent deformation. And the body always retains its original shape and size. This is called the elasticity of a material. So within this limit $ 0 $ and E, a material exhibits elasticity.
We can see that after point E there is no linear relationship between stress and strain. But until point Y a material will exhibit elasticity. The exact point Y is called the yield point or the elastic limit. If the external force is removed at this point then the material can retain its original position and if the external force is not removed at this point then the material cannot return to its original position and a plastic deformation begins to form. After the yield point is crossed the material is subjected to permanent deformation. The yield point that can also be called the elastic limit marks the end of the behavior of elasticity and the beginning of plastic behavior. When we remove the stresses less than the yield point, the material returns to its original shape.
After the point, Y is the force applied is increased then the length of the wire increases rapidly. This point between Y and U shows when the stress is zero then the strain will not be zero. In this state, the material is in permanent deformation that is called plastic deformation. This point U shows us the maximum limit of tensile. After this, we will reduce the applied force and that will result in the additional and the material will break out at point B. This is known as the breaking point of the material.

Note:
If the area between the U and B is large then the material is said to be tensile. If the area is small that is both points are close together then the material is said to be brittle. Both the elastic point and the yield point are essentially the same, but there is a difference between these two as they mark different limits. The elastic point gives us the end of the elasticity region, while the yield point gives us the beginning of the plasticity region.