18-01-2013, 09:54 AM
STRESS STRAIN AND DEFORMATION OF SOLIDS, STATES OF STRESS
STRESS STRAIN.doc (Size: 195.5 KB / Downloads: 34)
1. Define: Stress
When an external force acts on a body, it undergoes deformation. At the same time the body resists deformation. The magnitude of the resisting force is numerically equal to the applied force. This internal resisting force per unit area is called stress.
Stress = Force/Area
σ = P/A (unit is N/mm2)
2. Define: Strain
When a body is subjected to an external force, there is some change of dimension in the body. Numerically the strain is equal to the ratio of change in length to the original length of the body.
Strain = Change in length/Original length
e = ∂L/L
Q. Explain elastic strain energy.
Ans. When a body is loaded without exceeding elastic limit, it changes its dimensions. When the load is removed, it regains its original dimensions. For the period of time it has remained loaded, it stores energy in itself and this energy is called elastic strain energy.
3. Define: Elastic limit
Some external force is acting on the body, the body tends to deformation. If the force is
released from the body its regain to the original position. This is called elastic limit
4. State: Hooke’s law.
It states that when a material is loaded within its elastic limit, the stress is
directly proportional to the strain.
Stress α Strain
σαe
σ = Ee
Where, E - Young’s modulus in N/mm2
σ- Stress
e - Strain
5. Define: Young’s modulus
The ratio of stress and strain is constant with in the elastic limit. This constant is known as Young’s modulus.
E = Stress /Strain
3.8 RELATIONSHIP BETWEEN LOAD, SHEAR FORCE AND BENDING MOMENT
Consider a simply supported beam carrying audi of intensity w per unit length as shown in Fig. 3.15. Consider an elementary length of the beam of length ox between cross-
Sections
6. Define: shear stress and shear strain.
The two equal and opposite force act tangentially on any cross sectional plane of the body tending to slide one part of the body over the other part. The stress induced is called shear stress and the corresponding strain is known as shear strain.
7. Define: volumetric strain
The ratio of change in volume to the original volume of the body is called volumetric strain.
Volumetric strain= change in volume / original volume
ev = ∂V/V
8. Define: Poisson’s ratio
When a body is stressed, within its elastic limit, the ratio of lateral strain to the
longitudinal strain is constant for a given material.
Poisson’ ratio (μ or 1/m) = Lateral strain /Longitudinal strain
9. Define: Bulk-modulus
The ratio of direct stress to volumetric strain is called as bulk modulus..
Bulk modulus, K = Direct stress / Volumetric strain
10. Define: Shear modulus or Modulus of rigidity
The ratio of shear stress to shear strain is called as bulk modulus..
Shear modulus, G = shear stress / shear strain
11. What is compound bar?
A composite bar composed of two or more different materials joined together such that the system is elongated or compressed in a single unit.