Lecture 5 Chapter 7 Range of Mechanical Properties for Polymers TABLE 7.1 Material UTS (MPa) E (GPa) ABS 28 55 1.4 2.8 ABS, reinforced 100 7.5 Acetal 55 70 1.4 3.5 Acetal, reinforced 135 10 Acrylic 40 75 1.4 3.5 Cellulosic 10 48 0.4 1.4 Epoxy 35 140 3.5 17 Epoxy, reinforced 70 1400 21 52 Fluorocarbon 7 48 0.7 2 Nylon 55 83 1.4 2.8 Nylon, reinforced 70 210 2 10 Phenolic 28 70 2.8 21 Polycarbonate 55 70 2.5 3 Polycarbonate, reinforced 110 6 Polyester 55 2 Polyester, reinforced 110 160 8.3 12 Polyethylene 7 40 0.1 1.4 Polypropylene 20 35 0.7 1.2 Polypropylene, reinforced 40 100 3.5 6 Polystyrene 14 83 1.4 4 Polyvinyl chloride 7 55 0.014 4 Elongation (%) 75 5 75 25 50 5 100 5 10 1 4 2 300 100 200 60 10 1 2 0 125 10 6 4 300 5 3 1 1000 15 500 10 4 2 60 1 450 40 Poisson s ratio (ν) 0.35 0.35 0.40 0.46 0.48 0.32 0.40 0.38 0.38 0.46 0.35 1
From a Monomer to a Polymer Two main types of polymerization Condensation By-product formed Addition No byproduct formed Effect of Molecular Weight on Material Properties Molecular Weight g/mol Degree of polymerization Ratio of MW / mer weight Ethylene Gas : DP = 1 Liquid : DP = 6 Grease : DP = 35 Wax : DP = 140 Hard Plastic : DP = 1350 2
Types of Polymer Structures Bonding Primary Between mer groups Covalent Secondary Between polymer molecules Weak» Van der Waals»Hydrogen Strong» Ionic» Covalent Stress vs. Strain of Polymers 3
Amorphous and Crystalline Polymers Effect of Temperature on E 4
More Temperature Effects More Temperature Effects Glass transition temperature (T g ) Above T g Leathery Higher toughness Below T g Glassy Brittle 5
Elongation of Polymer Specimens (a) General Uses for Polymers TABLE 7.3 Design requirement Applications Plastics Mechanical strength Gears, cams, rollers, valves, fan blades, impellers, pistons Acetal, nylon, phenolic, polycarbonate Functional and decorative Handles, knobs, camera and battery cases, trim moldings, pipe fittings ABS, acrylic, cellulosic, phenolic, polyethylene, polypropylene, polystyrene, Housings and hollow shapes Functional and transparent Wear resistance Power tools, pumps, housings, sport helmets, telephone cases Lenses, goggles, safety glazing, signs, food-processing equipment, laboratory hardware Gears, wear strips and liners, bearings, bushings, roller-skate wheels polyvinyl chloride ABS, cellulosic, phenolic, polycarbonate, polyethylene, polypropylene, polystyrene Acrylic, polycarbonate, polystyrene, polysulfone Acetal, nylon, phenolic, polyimide, polyurethane, ultrahigh molecular weight polyethylene 6
Chapter 8 Composites Ceramic Parts (a) (b) Figure 8.1 A variety of ceramic components. (a) High-strength alumina for high-temperature applications. (b) Gas-turbine rotors made of silicon nitride. Source: Wesgo Div., GTE. 7
TABLE 8.1 Type Oxide ceramics Alumina Zirconia Carbides Tungsten carbide Titanium carbide Silicon carbide Nitrides Cubic boron nitride Titanium nitride Silicon nitride Sialon Cermets Silica Glasses Glass ceramics Graphite Diamond General Characteristics High hardness, moderate strength; most widely used ceramic; cutting tools, abrasives, electrical and thermal insulation. High strength and toughness; thermal expansion close to cast iron; suitable for heat engine components. Hardness, strength, and wear resistance depend on cobalt binder content; commonly used for dies and cutting tools. Not as tough as tungsten carbide; has nickel and molybdenum as the binder; used as cutting tools. High-temperature strength and wear resistance; used for heat engines and as abrasives. Second-hardest substance known, after diamond; used as abrasives and cutting tools. Gold in color; used as coatings because of low frictional characteristics. High resistance to creep and thermal shock; used in heat engines. Consists of silicon nitrides and other oxides and carbides; used as cutting tools. Consist of oxides, carbides, and nitrides; used in high-temperature applications. High temperature resistance; quartz exhibits piezoelectric effect; silicates containing various oxides are used in high-temperature nonstructural applications. Contain at least 50 percent silica; amorphous structures; several types available with a range of mechanical and physical properties. Have a high crystalline component to their structure; good thermalshock resistance and strong. Crystalline form of carbon; high electrical and thermal conductivity; good thermal shock resistance. Hardest substance known; available as single crystal or polycrystalline form; used as cutting tools and abrasives and as dies for fine wire drawing. Types and General Characteristics of Ceramics Mechanical Properties of Selected Ceramics TABLE 8.2 Material Symbol Transverse rupture strength (MPa) Compressive strength (MPa) Elastic modulus (GPa) Hardness (HK) Poisson s ratio (ν) Density (kg/m 3 ) Aluminum Al2O3 140 240 1000 2900 310 410 2000 3000 0.26 4000 4500 oxide Cubic boron CBN 725 7000 850 4000 5000 3480 nitride Diamond 1400 7000 830 1000 7000 8000 3500 Silica, fused SiO2 1300 70 550 0.25 Silicon SiC 100 750 700 3500 240 480 2100 3000 0.14 3100 carbide Silicon Si3 N4 480 600 300 310 2000 2500 0.24 3300 nitride Titanium TiC 1400 1900 3100 3850 310 410 1800 3200 5500 5800 carbide Tungsten WC 1030 2600 4100 5900 520 700 1800 2400 10,000 15,000 carbide Partially stabilized zirconia PSZ 620 200 1100 0.30 5800 Note: These properties vary widely depending on the condition of the material. Comparison of three main categories of materials E and UTS 8
Chapter 9 Composites Definition Composites Two or more chemically distinct and insoluble phases Typical components Matrix Metal Ceramic Polymer Fibers or particles Attractive properties High strength-to-weight ratio High stiffness-to-weight ratio 9
Composites Properties of Fibers Used to Reinforce Polymers TABLE 9.2 Type Tensile strength (MPa) Elastic modulus (GPa) Density ( kg/m 3 ) Relative cost Boron 3500 380 2600 Highest Carbon High strength 3000 275 1900 Low High modulus 2000 415 1900 Low Glass E type 3500 73 2480 Lowest S type 4600 85 2540 Lowest Kevlar 29 2800 62 1440 High 49 2800 117 1440 High Note: These properties vary significantly depending on the material and method of preparation. 10
Mechanical Property Comparison of Fiber Reinforced Composites Flexural Strength Effect of Fiber Orientation on Strength Figure 9.7 The tensile strength of glass-reinforced polyester as a function of fiber content and fiber direction in the matrix. Source: R. M. Ogorkiewicz, The Engineering Properties of Plastics. Oxford: Oxford University Press, 1977. 11