Factors affecting elasticity of a body
Mechanical properties of solids chapter
Answers
It is found that bodies lose their elastic limit, due to elastic fatigue. Therefore, the manufacture should choose the material in such a way that it should regain its elastic property even when it is subjected to large number of cycles of stress.
For example substances like quartz, phosphor, bronze etc. May be employed in manufacturing of galvanometers, electrometers etc, after knowing their elastic properties.
Apart from elastic fatigue some material will have change in their elastic property because of the following factors.
1. Effect of stress
2. Effect of annealing
3. Change in temperature
4. Presence of impurities
5. Due to the nature of crystals
a) Effect of stress: We know that when a material is subjected to large number of cycles of stresses, it loses its elastic property even within the elastic limit. Therefore the working stress on the material should be kept lower than the ultimate tensile strengthing and the safety factor.
b) Effect of Annealing: Annealing is a process by which the material is heated to a very high temperature and then it is slowly cooled. Usually this process is adopted for the material to increase the softness and ductility in the material. But if annealing is made to a material it results in the formation of large crystal grains, which ultimately reduces the elastic property of the material.
c) Effect of temperature: The elastic property of the materials changes with the temperature. Normally the elasticity increases with the decrease in temperature and vice-versa.
Examples
1. The elastic property of lead increases when the temperature is decreased.
2. The carbon filament becomes plastic at higher temperatures.
d) Effect of impurities: The addition of impurities produces variation in the elastic property of the materials. The increase and decrease of elasticity depends upon the type of impurity added to it.
Examples:
1. When potassium is added to gold, the elastic property of gold increases.
2. When carbon is added to molten iron, the elastic property of iron decreases provided the carbon content should be more than 1% in iron.
e) Effect of nature of crystals: The elasticity also depends upon the types of the crystals, whether it is a single crystal or poly crystals. For a single crystal the elasticity is more and for a poly crystal the elasticity is less.
Answer:
Effect of stress.
Effect of annealing.
Change in temperature.
Presence of impurities.
Due to the nature of crystals.