Friday, 9 March 2018

STRENGTH OF MATERIALS ke bare me jankari

STRENGTH OF MATERIALS

Elasticity = when an external force acts on a body, the body tends to undergo some deformation. If the external force is removed and the body returns to its original shape and size, then the body is known as elastic body. If the body comes in its original shape then it is called completely elastic body. Elastic limit marks the partial break down of elasticity beyond which removal of load result in a degree of permanent deformation. Steel, aluminum, and copper, concrete can be considered completely elastic within a certain range.




Plasticity = when an external force acts on a body, the body tends to undergo some deformation. If the external force is removed and the body does not return to its original shape and size, then the body is known as elastic body points to remember. This is useful in forging operations. Ductility = It is the material can be drawn into thin wire is called as ductility.  And material having the property of ductility is called as ductile material. Points to remember: Ductile material must have low degree of elasticity. It is useful in wire drawing. A ductile material should have a high level of plastic and power.


Brittleness = It is a property of material by virtue of which material can be break into number of part without any deformation. Points to remember: cast iron, concrete, Glass and ceramic material are brittle material. In brittle material failure take place under load without significant deformation. Malleability = It is the property of material by virtue of which it can be drawn into thin sheets without cracking by pressing , rolling, and hammering etc .points to remember: Toughness = It is the property of the material that enables it to absorb the energy of the fracture without it. Points to remember: Bend test used for common comparative test. Desirable in material which is subject to cyclic or shock loading.

Hardness = It has the ability to resist indentation or surface friction. Strength = It is defined as the maximum or limiting value of stress that material can withstand without a failure or fracture. It is property of material for mild steel {M.S.} Yield strength tension = 250 mpa Ultimate strength tension = 400 mpa Yield = permanent deformation ultimate = maximum points to remember: load required to cause fracture, divided by area of test specimen, is a ultimate strength.

STRESS = Force per unit area Where, 6= stress (also called intensity of stress) P= External force or load A= Cross - sectional area SI unit N/ Metre square. TYPES of stress:-Tensile stress Compressive stress Bending stress Tensile stress = It is the internal resisting force setup per unit cross sectional area under the action of axial pull. Compressive stress= It is internal resisting force setup per unit cross sectional area under the action of axial push. Shear stress = It is the internal resisting force setup per unit cross sectional area under the action of two tangential force.

Strain = it is dimension less ratio of change in length to its original length. It is denoted by 'e' TYPES of strain:-Tensile strain Compressive strain Volumetric strain Shear strain Tensile strain Increase in length / original length Compressive strain Decrease in length / original length Shear strain Strain produced by shear stress is known as shear strain Volumetric strain Change in volume to original volume.

Hooks law its state that when the material is loaded within elastic limit then stress is directly proportional to the strain and the proportionality constant is called as modulus of elasticity, modulus of rigidity or Elastic Modules. Modulus of rigidity or shear modulus Shear stress to shear strain Factor of safety Ultimate stress to permissible stress Bulk or volume modulus of elasticity Normal stress to volumetric strain Direct stress to volumetric strain Longitudinal strain = Increase in the length of the body in the direction of p. To length of body Lateral strain = increase in length to length Decrease in breath to original breath Decrease in depth to original depth Poisson’s ratio: - Lateral train to longitudinal strain

Analysis of bars of varying section. P= Axial load acting on the bar, L1= Length of section 1, A1= cross- sectional area of section 1, L2, A2 = Length and cross- sectional area if section 2, L3, A3 = Length and cross sectional area of section 3, E= Young’s modulus for the bar. Analysis of uniformly tearing circular bars A bar uniformly tapering from a diameter D1 at one end to a diameter D2 at the other end shown in Figure. P= axial Tensile load on the bar, L= total length of bar, E= young's modulus. Analysis of uniformly tapering Rectangular Bar A bar of constant thickness and uniformly tapering in width from one end to the other end. P= Axial load on the bar, L= Length of bar, a = width at bigger end= width at smaller end, E= Young’s modulus, t= Thickness of bar.

Engineering curve for mild steel for tension under static loading OA= straight line (proportional region, Hooks law is valid), OB= Elastic region, BC= Elasto plastic region, CD= perfectly plastic region, DE=Strain hardening, EF= Necking region, A= Limit of proportionality, B= Elastic limit, C= Lower yield point, D= Strain hardening starts, E= Ultimate stress, F= Fracture point. Equivalent young modulus of parallel composite bar P= Load, A1= Area of first bar, A2= Area of second bar, E1= young modulus of first bar, E2= young modulus of second bar, L= Length of bar . Volumetric strain under tri-axial loading Here,  6x= Stress in X- direction, 6y= Stress in y-direction, 6z = volumetric strain. Volumetric strain of cylindrical bar Ev= Longitudinal strain + (2 x Diametral strain ). Volumetric strain of sphere Ev= 3 x Diametrically strain .Relation between E, G, K, u E= Youngs modulus, G= shear modulus, K= Bulk modulus, U= position ratio,Thermal stress and strain 6= Thermal stress, a= coefficient of thermal expansion, T= Temperature change, ^ = change in length.

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