FEW BASIC CONCEPT OF STRENGTH OF MATERIALS
- 1. few basic concepts of Strength of materials Power point presentation By k. Anand Babu
- 2. Contents Stress ………………………………………………….2 Strain ………………………………………………….3 Types of stress ……………………………………………….....4-11 Elasticity and elastic limit ………………………………………………….11 Hooke’s law ….………………………………………………12 Young’s modulus ………………………………………………….12 Shear modulus …………………………………………………13 Factory safety ………………………………………………...13
- 3. Introduction when an external forces act on body, the body tends to undergo some deformation due to cohesion between the molecules ,the body resist deformation .this resistances by which material of body opposes the deformation is known as ‘strength of material’ Here the downward arrows are forces acts on body Hence the upward arrows are forces opposes the External forces from body body 1
- 4. stress The forces of resistances per unit area offered by a body against deformation is known as ‘stress’ Here the small circle in a rectangular section . the circle is the forces acting per unit area on rectangular section Is called stress the mathematical written as Stress=forces applied unit area area Units of Stress is Newton –meter square Here the forces unit is newton and area unit is meter square 2
- 5. Strain When a body is subjected to some external forces ,their is some change of dimension of the body The rate of change of dimension of the body to the original dimension Is known as ‘strain’ Strain = change in length original length Units of strain is no units Here the units of length is meter So meter/meter gets cancel 3
- 6. Types of stress and strain Types of stress and strain they are Stress; Stress may classified into two types they are Normal stress and Shear stress Normal stress is divided into two types Tensile stress Compressive stress Strain Strain is classified into four types they are Tensile strain Compressive strain Volumetric strain Shear strain 4
- 7. Normal stress Normal stress Is stress which acts in a direction perpendicular to the area it is represented by Sigma Tensile stress: the stress induced in a body when subjected to two equal and opposite pull As shown in fig as a result of which there is an increase in length is known as ‘tensile stress ‘ Tensile stress = resisting force /area Tensile stress Its units is newton /meter square 5
- 8. Compressive stress Tensile stress: the stress induced in a body when subjected to two equal and opposite pushes As shown in fig as a result of which there is an decrease in length of body is known as ‘compressive stress’ Compressive stress = resisting force / area Its units is newton /meter square 6
- 9. Shear stress The stress induced in a body ,when subjected to two equal and opposite forces which are acting tangentially Across the resting section as shown in fig as a result of which the body tends to shear off across the section Is known as ‘shear stress’ Its units is newton /meter square 7
- 10. Types of Strain Tensile strain If there is increase in length of body due to external load (or)external forces then the ratio of increase of Length to the original length of body is known as ‘tensile strain’ It has no units 8
- 11. Compressive strain If there is some decrease in length of the body then the ratio of decrease of length of the body to The original length of body is known as ‘compressive strain’ It has no units 9
- 12. Volumetric strain The ratio of change of volume of the body to the original volume of body is known as ‘volumetric strain’ It has no units 10
- 13. Shear strain Then produced by shear is known as shear strain Elasticity By virtue o which certain material returns back to their original position After the removal of the external forces is ‘elasticity’ EXTERNAL FORCES ACTING ON MATERIAL AFTER REMOVING FORCES 11 It has no units
- 14. ELASTICITY LIMIT Then body will regains its previous shape and size only when the deformation caused by the External forces is with in a certain limit while removing the external load .the deformation completely Disappears on body Hooke’s law Hooke’s law, states that when a material load with in elastic limit the stress is directly proportional to The strain produced by the stress . This means the ratio of the stress to the corresponding strain is A constant with in the elastic limit this constant is known as ‘modulus of elasticity’ (or) ‘modulus of rigidity’(or) ‘elastic moduli’ Its units is newton /meter square 12
- 15. Modulus of elasticity (or) young’s modulus The ratio of tensile stress (or) compressive stress to corresponding strain is a constant This ratio is known as ‘young’s modulus’ it is denoted by ‘E’ Its units is newton /meter square 13
- 16. Modulus of rigidity (or) shear modulus The ratio of the shear stress to the corresponding shear strain with in the elastic limit is known as ‘modulus of rigidity’ (or) ‘shear modulus’ It is denoted by C ,G or N Factor of safety It is define as the ratio of ultimate stress to the working stress(or) permissible stress (or) design load is known as ‘factor of safety’ 14