Edexcel AS Physics Unit 1 : Chapter 7: Solid Materials Prepared By: Shakil Raiman

7.1 Elastic Deformation A material undergoing elastic deformation will return to its original dimensions when the deforming force is removed. Example: Spring, Steel wire etc.

7.2 Plastic Deformation A material undergoing plastic deformation will not return to its original dimensions or remain deformed when the deforming force is removed. Example: modelling clay

7.3 Elastic and Plastic Deformation Some material can behave in an elastic or plastic manner depending on the nature of the deforming force. A thin steel sheet will deform elastically when small forces are applied to it, but the huge forces of a hydraulic press will mould the sheet into car panels.

7.4 Properties of Solid Materials Hardness: Hardness is a surface phenomenon. The harder the material, the more difficult it is to indent or scratch the surface. Diamond is hardest which has a rating 10. Stiffness: A stiff material exhibits very small deformations even when subjected to large force. Steel etc.

7.4 Properties of Solid Materials Strength: An object is strong if it can withstand a large force before it breaks. Steel is strong but cotton is weak. Malleability: A malleable material can be hammered out into thin sheets. Gold

7.4 Properties of Solid Materials Ductility: Ductile materials can be drawn into wires. copper

7.5 Stress Stress (tensile/compressive stress) is defined as force per unit cross-sectional area. Unit: Pa (Pascal)

7.6 Strain Strain is defined as extension per unit original length. Unit: no unit

7.7 Young’s Modulus Young modulus is defined as the ratio of tensile or compressive stress to strain. Unit: Pa (Pascal)

7.8 Hooke’s Law Hooke’s law states that, upto a given load, the extension of a spring (or wire) is directly proportional to the force applied to the spring (or wire) where K represents the stiffness or spring constant

7.9 Elastic Potential Energy or Elastic Strain Energy The elastic potential energy or elastic strain energy is the ability of a deformed material to do work as it regains its original dimensions.

7.10-1: Stress-Strain Graph

7.10-2: Stress-Strain Graph O-A represents the Hooke’s Law region. Strain is proportional to stress up to this point. The Young modulus of material can be found directly by taking the gradient in this section. B is the elastic limit. If the stress is removed below this value, the wire returns to its original state.

7.10-3: Stress-Strain Graph C is the yield stress. For stresses greater than this, the material will become ductile and deform plastically. D is the maximum stress that a material can endure. It is called ultimate tensile strength (UTS). E or F is the breaking point. After E the wire starts narrowing.

7.10-4: Stress-Strain Graph

7.10-5: Stress-Strain Graph

7.10-6: Stress-Strain of Rubber The hysteresis loop for stress-strain graph represents the energy per unit volume transferred to internal energy during load-unload cycle.

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