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### Som 1

1. 1. CHAPTER 1 SIMPLE STRESS & STRAIN Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
2. 2. Simple stress & strain Basic Definitions Faculty Name Dept. LJ Polytechnic  Elasticity : When the material is loaded it deforms, but when this load is removed the material regains its original shape. This property of material is called elasticity.  Plasticity : It is a permanent deformation of material. The material does not regain its original shape after the load is removed.  Ductility : The materials which can withstand a very high tensile loads are called ductile materials. Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
3. 3. Simple stress & strain Basic Definitions Faculty Name Dept. LJ Polytechnic  Malleability : The materials which can withstand a very high compressive stress are called malleable materials.  Toughness : the energy absorbed by material before failure is called toughness of material.  Hardness : The materials which can not be deformed are called hard materials.  Strain energy : The energy stored in the material within elastic limit is called strain energy. Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
4. 4. Simple stress & strain Basic Definitions Faculty Name Dept. LJ Polytechnic  Stress : When the load is applied on the material the internal resistance is produced in the material which resist this external load. This resistance pre unit area is called stress.  Strain : It is the ratio of change in the dimension to the original dimension of material.  Hook’s law : The stress is directly proportional to strain within the elastic limit. So This E is called young's modulus or modulus of elasticity. Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
5. 5. Simple stress & strain Basic Definitions  Lateral strain : The strain in the perpendicular direction of linear strain is called lateral strain. Poisson’s ratio : It is the ratio of lateral strain to linear strain.  It is denoted by µ.  Bulk modulus : It is the ratio of stress to the volumetric strain.  It is denoted by K. Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
6. 6. Simple stress & strain Basic Definitions  Types of loads : (i) Tensile (ii) Compressive  Shear stress : TENSILE COMPRESSI VE Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
7. 7. Simple stress & strain Stress – strain curve  Stress strain curve : Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
8. 8. Simple stress & strain Stress – strain curve Faculty Name Dept. LJ Polytechnic  Elastic limit : The region up to point A as shown in figure is called elastic region in which stress is directly proportional to strain. Yield Point stress : It is the value of stress after which the strain increases in a large amount with very small change in stress. (point C) Plastic region : When the load is applied beyond plastic region, it deforms permanently so this region is called plastic region. Ultimate stress : The maximum amount of load a material can withstand is called ultimate stress.(shown as point E) Fracture point : The stress at which the material fails.(Point F) Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
9. 9. Simple stress & strain Thermal stress Thermal stress : When the material is heated, it expands. Now if this expansion is restricted by some means then the stress developed in the material is called thermal stress. Expansion due to temperature : Stress due to temperature : Expansion when yielded by length : Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
10. 10. Simple stress & strain Strain energy in gradual loading Faculty Name Dept. LJ Polytechnic  Types of loading : (1) Gradual loading (2) Sudden loading (3) Impact loading (1) Gradual loading: Strain Energy = Area of Diagram = ½ * P * l = Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
11. 11. Simple stress & strain Strain energy in sudden loading Faculty Name Dept. LJ Polytechnic (2) Sudden loading : Strain energy = Area of diagram = P * l = We can see the strain energy stored in body in sudden loading is double than stored in gradual loading. Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
12. 12. Simple stress & strain Strain energy in impact loading Faculty Name Dept. LJ Polytechnic (3) Impact loading : When the load is applied with some initial velocity then it is called impact loading. If a weight W falls from height h on a body and deforms a body by then the work done by weight on the body is = W (h + ) This work done is stored as strain energy in the material. Faculty Name : MISSAM RAZA Dept. MECH LJ Polytechnic
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