Physics Of Materials-Classical Physics-Handouts, Lecture notes of Classical Physics

Download Physics Of Materials-Classical Physics-Handouts and more Lecture notes Classical Physics in PDF only on Docsity! PHYSICS –PHY101 VU © Copyright Virtual University of Pakistan 47 Summary of Lecture 17 – PHYSICS OF MATERIALS 1. the property by virtue of which a body tends to regain its original shape and size when external forces are removed. If a body completely recovers its original shape and size , i Elasticity : t is called perfectly elastic. Quartz, steel and glass are very nearly elastic. 2. if a body has no tendency to regain its original shape and size , it is called perfectly plastic. Commo Plasticity : n plastics, kneaded dough, solid honey, etc are plastics. 3. characterizes the strength of the forces causing the stretch, squeeze, or twist. It is defined usually as force/unit area but may Stress have different definitions to suit different situations. We distinguish between three types of stresses: a) If the deforming force is applied along some linear dimension of a body, the stress is called or or b) If the force acts normally and uniformly from all sides of a body, the stress is called . c) longitudinal stress tensile stress compressive stress. volume stress If the force is applied tangentially to one face of a rectangular body, keeping the other face fixed, the stress is called tangential or shearing stress. 4. Strain: When deforming forces are applied on a body, it undergoes a change in shape or size. The fractional (or relative) change in shape or size is called the strain. change i Strain = n dimension original dimension Strain is a ratio of similar quantities so it has no units. There are 3 different kinds of strain: a) is the ratio of the change in leLongitudinal (linear) strain ngth ( ) to original length ( ), i.e., the linear strain . b) is the ratio of the change in volume ( ) to original volume ( ) Volume strain . c) L ll l Volume strain V V V V Shearing strain : Δ Δ = Δ Δ = The angular deformation ( ) in radians is called shearing stress. For small the shearing strain tan .x l θ θ θ θ Δ≡ ≈ = l xΔ θ F docsity.com PHYSICS –PHY101 VU © Copyright Virtual University of Pakistan 48 5. Hooke's Law: for small deformations, stress is proportional to strain. Stress = E × Strain The constant is called the modulus of elasticity. hasE E the same units as stress because strain is dimensionless. There are three moduli of elasticity. (a) Young's modulus (Y) for linear strain: longitudina Y ≡ l stress / longitudinal strain / (b) Bulk Modulus (B) for volume strain: Let a body of volume be subjected to a uniform pressure on its entire surface and let be the correspond F A l l V P V = Δ Δ Δ ing decrease in its volume. Then, Volume Stress B . Volume Strain / 1/ is called the compressibility. A material having a small value of P V V B Δ ≡ = − Δ B can be compressed easily. (c) Shear Modulus ( ) for shearing strain: Let a force F produce a strain as in the diagram in point 4 above. Then, η θ shearing stress / . shearing strain tan 6. When a wire is stretched, its length increases and radius decreases. The ratio of the lateral strain to the longitudinal strain is c F A F Fl A A x η θ θ ≡ = = = Δ /alled Poisson's ratio, . Its value lies / between 0 and 0.5. 7. We can calculate the work done in stretching a wire. Obviously, we must do work against a force. If x is the extension pr r r l l σ Δ= Δ ( )2 0 0 oduced by the force in a wire of length , then . The work done in extending the wire through is given by, 2 l l F l YAF x l l lYA YAW Fdx xdx l l Δ Δ = Δ Δ = = =∫ ∫ ( ) ( ) 2 1 1 volume stress strain 2 2 2 1 Hence, Work / unit volume stress strain. We can also write this as, 2 1 2 lYA Y l lAl l l l YA lW l Δ Δ Δ⎛ ⎞⎛ ⎞= = = × × ×⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠ = × × Δ⎛ ⎞= ⎜ ⎟ ⎝ ⎠ 1 load extension. 2 lΔ = × × docsity.com