Engineering Materials PDF

ENGINEERING MATERIALS ENGINEERING MATERIALS ENG-G001  Materials in Manufacturing The basic knowledge of engineering materials and their (Physical and mechanical) properties is of great significance for a design and manufacturing engineer. ENG-G001 Classific...

ENGINEERING MATERIALS ENGINEERING MATERIALS ENG-G001  Materials in Manufacturing The basic knowledge of engineering materials and their (Physical and mechanical) properties is of great significance for a design and manufacturing engineer. ENG-G001 Classification of Engineering Materials ENG-G001  Selection of materials A material is selected for any specific application according to: 1- Properties -mechanical-physical and also manufacturing properties 2- Processing -the method of processing may affect the product's final properties, service, life and cost. 3- Cost and availability. ENG-G001  Metals Why Metals Are Important 1-High stiffness and strength - can be alloyed for high rigidity, strength, and hardness. 2-Toughness - capacity to absorb energy better than other classes of materials. 3-Good electrical conductivity 4-Good thermal conductivity 5- They are relatively ductile. 6- Some have good magnetic properties. 7-Cost – the price of steel is very competitive with other engineering materials ENG-G001  Classification of Metals A-Ferrous Metals such as :steels and cast iron B- Nonferrous Metals such as: Aluminum, magnesium, copper, nickel, titanium, zinc, lead, tin, molybdenum, tungsten, gold, silver, platinum, and others ENG-G001  Pure Metals and Alloys Some metals are important as pure elements (e.g., gold, silver, copper) Most engineering applications require the enhanced properties obtained by alloying Through alloying, it is possible to increase strength, hardness, and other properties compared to pure metals An alloy is a mixture or compound of two or more elements, at least one of which is metallic. ENG-G001  An alloy ENG-G001  Materials Properties and Selection When selecting a material for a product or application, it is important to ensure that its properties will be adequate for the anticipated operating conditions. Selected Materials must possess the desired properties within their range of applications. These properties typically include: Mechanical properties which determine a material’s behavior when subjected to mechanical loading under the given environmental conditions. These include properties such as ductility, strength, rigidity, resistance to fracture, and the ability to withstand vibrations or impacts. Physical properties that include such features as density (weight); melting point; the thermal properties and thermal conductivity; electrical conductivity; and magnetic properties. Features relating to the service environment which indicate ability to operate under extremes of temperature or to resist corrosion. ENG-G001  Physical Properties in Manufacturing Fusibility: It is the ability of the materials to change its state from solid to liquid by heating Refractoriness: The resistance of the material to change in state and shape under the effect of heating Thermal conductivity: The rate of heat transfer measured in J/m.s.C Density, electrical resistivity, color,……..etc ENG-G001  Mechanical Loading: Types of Static Stress and Strains When a force or load is applied to a material, it deforms or distorts i.e. it becomes strained, and internal reactive forces (stresses) are transmitted through the solid. Three basic types of static strains to which materials can be subjected: a-Tensile – e.g. Tensile strains as involved in stretching sheet metal to make car bodies. b- Compressive – e.g. Compressive strains as in forging metals to make turbine disks, C- Shear – e.g. Shearing a blank from a sheet metal.(Source: Kalpakjian&Shmid) The simple tension test is the most common test for studying stress-strain relationship, especially for metals. In the test, a force pulls the material, elongating it and reducing its diameter. ENG-G001  Engineering Stress and Strain in Tension Test Stress: Defined as Strain: Defined at any force divided by stage in the test as original area L  Lo F e e  Lo Ao where e = where e = engineering strain; L = length at any stage during engineering elongation; and Lo = original stress, F = applied gage length force, and Ao = Tensile test: (a) original area of tensile force applied test specimen in (1) and in (2) resulting elongation and reduction in diameter of material. ENG-G001 (Source:Groover)  Tensile Test Sequence: Ductility and Tensile Strength Typical progress of a tensile test: (1) beginning of test, no load; (2) uniform elongation and reduction of cross-sectional area; (3) continued elongation, maximum load reached; (4) necking begins, load begins to decrease; and (5) fracture. If pieces are put back together as in (6), final length can be measured. The Total Elongation EL up to fracture is a measure of Ductility.(Source:Groover) Elongation is accompanied by a uniform reduction in cross-sectional area, consistent with maintaining constant volume. Finally, the applied load F reaches a maximum value, and engineering stress at this point is called the Tensile Strength TS (a.k.a. ultimate tensile strength) Lf  Lo EL  Lo Fmax Ao ENG-G001 Stress and strain relationship for ductile material (mild steel) ENG-G001  Typical Engineering Stress-Strain Plot There are two regions that indicate two distinct forms of behavior, namely elastic region and plastic region: 1. Elastic region – prior to yielding of the material.. Relationship between stress and strain is linear. Material returns to its original length when stress is removed. As stress increases, a point in the linear relationship is finally reached when the material begins to yield. Yield point Y can be identified by the change in slope at the upper end of the linear region. Y = a strength property. Other names for yield point = yield strength, yield stress, and elastic limit. 2. Plastic region – after yielding of the material. Yield point marks the beginning of plastic (permanent) deformation. The stress-strain relationship is no Typical engineering stress-strain longer linear. plot in a tensile test of a metal. (Source:Groover) As load is increased beyond Y, elongation proceeds at a much faster rate than before, causing the slope of the curve to change dramatically. Soon after the maximum load point, material necks and fracture at the maximum elongation (ductility limit) EL. ENG-G001  Elastic Region in Engineering Stress-Strain Curve Relationship between stress and strain is linear. Material returns to its original length when stress is removed Hooke's Law: e = E e where E = modulus of elasticity E is a measure of the inherent stiffness of a material Its value differs for different materials ENG-G001  True Stress and True Strain True strain : Defined at True stress : Defined as any stage in the test force divided by as current deformed area:  F   Ln( L / Lo) A where where  = True stress,  = True strain; L = length F = applied force, and at any stage during A = Current deformed elongation; and Lo = area of test specimen original gage length ENG-G001  True Stress-Strain Curve Note that true stress increases continuously in the plastic region until necking It means that the metal is becoming stronger as strain increases This is the property called strain hardening ENG-G001  Mechanical Properties It may be specifically defined as the properties which relate to the behavior of the material when subjected to the acting loads Fundamental mechanical properties are:- 1-Elasticity. It is the ability of the material to return to its original dimensions upon the removal of the external applied load. ENG-G001 3-Hardness. It is commonly defined as the ability of a material to resist abrasion or indentation 4-Brittleness. It is the property of the material which makes it fractured before much or no deformation is noticeable. 5-Strength. It is the resistance of the material to an applied force measured in stress units 6-Toughness. The property of the material to withstand or absorb mechanical energy e.g. shocks and blows. 7-Malleability. It is the ability of a material to stand large plastic compressive deformation, ENG-G001 8- Plasticity. It is the property which permits materials to undergo permanent change in shape without fracture 9-Stiffness. It is the property of the material to resist any sort of deformation. 10- Resilience. It is the capacity of the material to store mechanical energy 11-Fatigue. the failure of a material under the action of repeated alternating stresses 12- Endurance. It is the property of the material to withstand repeated application of the load ENG-G001 Stress and strain relation for brittle and ductile materials ENG-G001  Steel An alloy of iron containing from 0.025% and 2.11% carbon by weight 1-Plain carbon steels may contain: up to 0.3% silicon, up to 0.05% Sulphur. up to 0.05% phosphorus. up to 0.1% to 1.4% carbon. up to 1.0% manganese. Its strength increases with carbon content, but ductility is reduced. It can be grouped into three categories: ENG-G001  1- Low Carbon Steel Contains carbon up to 0.3%. Can be divided to;- A- dead mild steel (0.1 to 0.15% carbon content) It is very ductile and very soft, it is used for manufacturing of car body without cracking, rivets and pipes B- Mild steel (0.15% and 0.3% carbon content) It is available in different forms including wires, rods, angle and channel sections, pipes and sheets. It is used in engineering components such as bolts, nuts, chains, and bridges. ENG-G001  2-Medium carbon steels (0.3% to 0.8% carbon) There are two groups of medium carbon steels: -From 0.3% to 0.5% carbon. used for such products as drop-hammer ,die blocks, leaf Springs , wire ropes, screws, hammer heads and heavy-duty forgings. - from 0.5% to 0.8% carbon used for such products as wood saws, cold chisels, crankshafts, gears and other stressed components such as high-tensile pipes and tubes. ENG-G001  3-High carbon steels (above 0.8%). These are harder, less ductile and more expensive than both mild and medium carbon steels. They are mostly used for springs, cutting tools and forming dies - From 0.8% to 1.0% carbon where both toughness and hardness are required. For example, chisels, some hand tools, shear blades. - From 1.0% to 1.2% carbon for sufficient hardness for most metal cutting tools for example wood-drills, screw-cutting taps and screw-cutting dies. - From 1.2% to 1.4% carbon where extreme hardness is required for wood-working tools and knives, dividers, Vernier caliper, files. ENG-G001  2- Alloy steels The most common alloying elements are: Nickel, to refine the grain and strengthen the steel. Chromium, to improve the corrosion resistance of the steel. Molybdenum, to reduce temper brittleness during heat treatment,. Manganese improves the strength and wear resistance of steels. Tungsten and cobalt, improve the ability of steels to remain hard at high temperatures. ENG-G001  3-Stainless steels Groups of stainless steels Ferritic stainless steel which has 14% chromium but only 0.04%carbon and 0.5% nickel and has the lowest strength and corrosion resistance of the stainless steels. Martensitic stainless steel has 13% chromium, 0.3% carbon and 1.0% nickel. It can be quench hardened. Austenitic stainless steel has 18% chromium, 0.1% carbon and 8%nickel; hence it is widely known as 18/8 stainless steel. It is the most corrosion resistant of all the stainless steels ENG-G001  4-Tool steels They are designed for use as industrial cutting tools, dies, and molds. They must possess high strength, hardness, hot hardness; wear resistance, and toughness under impact. ENG-G001  Cast Irons These are also ferrous metals containing iron and as much as 4% carbon and from 1% to 3% silicon. Most important is gray cast iron. Other types include ductile iron, white cast iron, malleable iron, and various alloy cast irons. ENG-G001  Grey cast iron Grey cast iron with laminar graphite High compressive strength, low tensile strength, brittle, good damping and sliding properties Its applicatin:1-Piston, 2-Piston ring, 3-Cylinder 4-Housing. Grey cast iron with spherical graphite It has high compressive strength, high tensile strength and ductile. Crank shaft, Gear, Gearbox ENG-G001  Nonferrous Metals Aluminum - Its density =2.7 gmlcm3-melting point=660 C - High electrical and thermal conductivity - Excellent corrosion resistance due to formation of a hard thin oxide surface film It can be produced in the form of thin sheets, wires, tubes or solid sections. The most important alloys are: Al-Cu-Mg, Al-Mg-Si and Al-Cu-Ni Aluminum is used in buildings and construction, containers and packaging, transportation and electrical conductors ENG-G001  Copper - its density=8,97 gmlcm3, melting point =1083 C - Low electrical resistivity - Is widely used as motor car radiators , Wires for electrical windings and conductors. Sheets as water tanks in food and chemical industries. Tubes; for heat exchangers The most important alloys are: 1- Copper-Zinc (brasses) 2- Copper-Tin (Bronze) 3- Copper-Aluminum (aluminum bronze) ENG-G001  Titanium and Its Alloys Abundant in nature, constituting  1% of earth's crust (aluminum is  8%) Density of Ti is 4.5 gm/cm3. It used in aerospace applications (aircraft and missile ) it is used for corrosion resistant components, such as marine components Titanium alloys are used as high strength components at temperatures ranging up to above 550C (1000F), ENG-G001  Lead and Tin Often considered together due to their low melting points and use in soldering alloys Lead – density 11.3 gm/cm3, low melting point (327 C); low strength, low hardness, high ductility, good corrosion resistance Applications: solder, bearings, x-ray shielding, storage batteries, and vibration damping Tin – density 7.2 gm/cm3 lower melting point (232 C) ; low strength, low hardness, good ductility Applications: solder, bronze, "tin cans" for storing food ENG-G001  Ceramics They are containing metallic (or semi- metallic) and nonmetallic elements. For processing, ceramics divide into: 1-Crystalline ceramics – includes : Traditional ceramics, such as clay (hydrous aluminum silicates). Modern ceramics, such as alumina (Al2O3) 2-Glasses – mostly based on silica (SiO2) ENG-G001  Physical Properties of Ceramics Density –most ceramics are lighter than metals but heavier than polymers Melting temperatures - higher than for most metals Some ceramics decompose rather than melt Electrical and thermal conductivities - lower than for metals, so some ceramics are insulators while others are conductors Thermal expansion - somewhat less than for metals, ENG-G001  Polymers Compound formed of repeating structural units called mers. Most polymers are based on carbon and are therefore considered organic chemicals. Polymers can be divided into three categories: 1-Thermoplastic polymers - can be subjected to multiple heating and cooling cycles without altering molecular structure Polyethylene, polyvinylchloride, polystyrene, and nylon 2-Thermosetting polymers - cannot be reheated , epoxies, and certain polyesters 3-Elastomers - shows significant elastic behavior ENG-G001 Various structures of polymer molecules: (a) linear,(b) branched characteristics of thermoplastics. (c) loosely cross-linked characteristic of an elastomer.(d) tightly cross-linked structure as in a thermoset ENG-G001  Polymer Products Thermoplastic products include Molded and extruded items, Fibers and filaments Films and sheets. Packaging materials Paints and varnishes Thermoset products include pot handle, electrical switch cover, plywood adhesives, paints, molded parts, printed circuit boards ,fiber reinforced plastics ENG-G001  Composites Material consisting of two or more phases that are processed separately and then bonded together to achieve properties superior to its constituents Phase - homogeneous mass of material, such as grains of identical unit cell structure in a solid metal Usual structure consists of particles or fibers of one phase mixed in a second phase Examples: Cemented carbides (WC with Co binder) Rubber mixed with carbon black ENG-G001  Classification of Composites Most composite materials consist of two phases: 1-Primary phase - forms the matrix within which the secondary phase is imbedded 2-Secondary phase - imbedded phase sometimes referred to as a reinforcing agent, the reinforcing phase may be in the form of fibers, particles, or various other geometries ENG-G001 According to the type of matrix, composites could be classified as: 1-Metal Matrix Composites (MMCs) - mixtures of ceramics and metals, such as cemented carbides 2-Ceramic Matrix Composites (CMCs) - Al2O3 and SiC imbedded with fibers to improve properties 3-Polymer Matrix Composites (PMCs) - polymer resins imbedded with filler or reinforcing agent ENG-G001  Laminar Composite Structure Two or more layers bonded together in an integral piece. Laminar composite structures: (a) conventional laminar structure, (b) sandwich structure using foam core, (c) sandwich structure using honeycomb core. ENG-G001  examples plywood, in which layers are the same wood, but grains are oriented differently to increase overall strength Automotive tires - multiple layers of rubber bonded together with reinforcing agent Fiber-reinforced plastic panels for aircraft, boat hulls, Printed circuit boards - layers of reinforced copper and plastic for electrical conductivity and insulation, Wind shield glass - two layers of glass on either side of a sheet of tough plastic ENG-G001