1. Chapter 3 Physical Properties of Materials

2. PHYSICAL PROPERTIES 1. Density 2. Melting point 3. Specific heat 4
PHYSICAL PROPERTIES 1. Density 2. Melting point 3. Specific heat 4. Thermal conductivity 5. Coefficient of thermal expansion 6. Electrical resistivity/conductivity 7. Corrosion resistance

3. 1. DENSITY Mass per unit volume 1
1.DENSITY Mass per unit volume 1. Important in the case of weight saving (aircraft, automobiles, sporting goods, laptops) 2. Important in the case of high speed equipment (alumimium in digital cameras, ceramics in high speed automated machinery) 3. Important for the case in which weight is desirable ( counterweights, flywheels, ballasts on yachts e.g. tungsten)

4. 2. MELTING POINT metals have a definite value alloys have a range (depending upon their composition) 1.Has an effect on manufacturing operations (annealing, heat treatment, hot working) 2.Important in the case of choosing tool and die materials 3. Casting

5. 3. SPECIFIC HEAT Energy required to raise the temperature of a unit mass by one degree (J/kgK) Excessive temperature rise in a work piece can: 1. Decrease product quality (affecting surface finish and dimensional accuracy) 2. Cause excessive tool wear and die wear 3. Result in undesirable metallurgical changes in the material

6. 4.THERMAL CONDUCTIVITY Rate at which heat flows through a material Metals have high values, plastics and ceramics have poor conductivity High thermal conductivity: cooling fins, cutting tools, die casting molds Low thermal conductivity : furnace lining, insulation, handles for pots, coffee cups)

7. 5. THERMAL EXPANSION inversely proportional to melting point important in forging processes (hot work piece placed on a cold die) may lead to cracking/warping/loosening of components low expansion alloys (iron nickel alloys)

8. 6. ELECTRICAL CONDUCTIVITY mho/m ELECTRICAL RESISTIVITY ohm/m Important in resistance welding Alloying has a major effect Conductors: materials with high electrical conductivity Insulators (dielectrics): materials with high electrical resistivity

9. 7. CORROSION RESISTANCE causes: chemical reactions, environmental oxidation Important in chemical, food and petroleum industries High corrosion resistance materials: non ferrous metals, stainless steel and non metallic materials Poor corrosion resistance materials: steel and cast iron Pitting: localized corrosion

10. TABLE 3.1 Physical Properties of Selected Materials at Room Temperature

11. TABLE 3.1 (continued) Physical Properties of Selected Materials at Room Temperature

12. TABLE 3.2 Physical Properties of Materials (in Descending Order)

13. FIGURE 3.1 Ratio of maximum yield stress to density for selected metal alloys.

14. FIGURE Specific strength (tensile strength/density) and specific stiffness (elastic modulus/density) for various materials at room temperature. (See also Chapter 9.)

15. FIGURE Specific strength (tensile strength/density) for a variety of materials as a function of temperature; note the useful temperature range for these materials and the high values for composite materials. MMC = metal-matrix composite; FRP = fiber-reinforced plastic.

16. FIGURE 3. 4 A selection of U. S
FIGURE A selection of U.S. coins, manufactured from different metal alloys of copper, nickel, tin, zinc, and aluminum. Valuable metals such as gold and silver are used for coins, but are not used for general currency.

17. GENERAL CRITERIA FOR THE SELECTION OF THE MATERIALS OF COINS 1
GENERAL CRITERIA FOR THE SELECTION OF THE MATERIALS OF COINS 1. Subjective factors: appearance, color, weight, ringing, feel 2. Intended life: resistance to corrosion and wear (affects imprint and luster) 3. Manufacturing (formability) 4. Suitability for use in coin operated devices 5. Health issues: nickel allergies 6. Cost of raw materials and manufacturing (one cent costs 1.6 cents to manufacture)