Lecture 5. Chapter 7. Range of Mechanical Properties for Polymers. The University of New Mexico. The University of New Mexico TABLE 7.

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1 Lecture 5 Chapter 7 Range of Mechanical Properties for Polymers TABLE 7.1 Material UTS (MPa) E (GPa) ABS ABS, reinforced Acetal Acetal, reinforced Acrylic Cellulosic Epoxy Epoxy, reinforced Fluorocarbon Nylon Nylon, reinforced Phenolic Polycarbonate Polycarbonate, reinforced Polyester 55 2 Polyester, reinforced Polyethylene Polypropylene Polypropylene, reinforced Polystyrene Polyvinyl chloride Elongation (%) Poisson s ratio (ν)

2 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 =

3 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

4 Amorphous and Crystalline Polymers Effect of Temperature on E 4

5 More Temperature Effects More Temperature Effects Glass transition temperature (T g ) Above T g Leathery Higher toughness Below T g Glassy Brittle 5

6 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

7 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

8 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 Al2O oxide Cubic boron CBN nitride Diamond Silica, fused SiO Silicon SiC carbide Silicon Si3 N nitride Titanium TiC carbide Tungsten WC ,000 15,000 carbide Partially stabilized zirconia PSZ Note: These properties vary widely depending on the condition of the material. Comparison of three main categories of materials E and UTS 8

9 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

10 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 Highest Carbon High strength Low High modulus Low Glass E type Lowest S type Lowest Kevlar High High Note: These properties vary significantly depending on the material and method of preparation. 10

11 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,