Hardness
It is the ability of a material to withstand scratching (abrasion) or indentation by another hard body, it is an indication of the wear resistance of the material. For example, figure shows a hardened steel ball being pressed first into a hard material and then into a soft material by the same load. As seen that the ball only makes a small indentation in the hard material but it makes a very much deeper impression in the softer material.
Density
Density is defined as mass per unit volume for a material. The unit is usually kg/m³. Relative density is the density of the material compared with the density of the water at 4°C.. The formulae of density and relative density are:
Strength
Strength is the ability of a material to resist applied forces without fracturing.
Tensile Strength
It is the ability of a material to withstand tensile (stretching ) loads without breaking.
Wear Resistance
When two surfaces slide against each other, material will be removed from both of them. or Resistant to damage from normal wear or usage
Its wear-resistant parts are used to combat damage to machinery caused by high and corrosion.
However Wear Resistance can also be looked at as the durability of the property. Machine components that come into contact with each other need to have high Wear Resistance.
Corrosion Resistance
Corrosion resistance refers to the resistance a material offers against the reaction with adverse elements which can corrode the material.
Essentially, corrosion is the process in which a material is oxidized by the environment and loses electrons in its result. Therefore, corrosion resistance is the capability to hold that binding energy of metal and withstand the deterioration and chemical breakdown that occurs during surface to such an environment.
Toughness
It is the ability of the materials to withstand bending or it is the application of shear stresses without fracture, so the rubbers and most plastic materials do not shatter, therefore they are tough.
Ductility
It refer to the capacity of substance to undergo deformation under tension without rupture as in wire drawing (as shown in figure), tube drawing operation.
Malleability
It is the capacity of substance to withstand deformation under compression without rupture or the malleable material allows a useful amount of plastic deformation to occur under compressive loading before fracture occurs. Such a material is required for manipulation by such processes as forging, rolling and rivet heading as shown in figure.
Elasticity
It is the ability of a material to deform under load and return to its original size and shape when i the load is removed. If it is made from an elastic material it will be the same length before and after the load is applied, despite the fact that it will be longer whilst the load is being applied. All materials possess elasticity to some degree and each has its own elastic limits. As in figure.
Thermal Conductivity
It is the property of a material which represents that how easily the heat can be conducted by material.
The thermal conductivity of a material can be defined as "the amount of heat transmitted by unit thickness of material normal to the unit area surface in unit time when the temperature gradient across the material piece is unity in steady state condition. Its unit in SI system is watts per meter per "K.
This is the ability of the material to transmit heat energy by conduction. Figure 2 shows a soldering iron. The bit is made from copper which is a good conductor of heat and so will allow the heat energy stored in it to travel easily down to the tip and into the work being soldered. The wooden handle remains cool as it has a low thermal conductivity and resists the flow of heat energy.
Electrical Conductivity
It is the property of material which represents that how easily the electricity can be conducted by the material. It is denoted by 'o'. It is the reciprocal of resistivity of material. It unit is mho/meter.
Electrical conductivity is a measure of how well a material accommodates the movement of an electric charge.
Figure 1 shows a piece of electrical cable. In this example copper wire has been chosen for the conductor or core of the cable because copper has the property of very good electrical
Conductivity
That is, it offers very little resistance to the flow of electrons (electric current) through the wire. A plastic materials such as polymerized has been chosen for the insulating sheathing surrounding the wire conductor. This material has been chosen because it is such a bad conductor, where very few electrons can pass through it. Because they are very bad conductors they are called as insulators. There is no such thing as a perfect insulator, only very bad conductors.
For example, metallic conductors of electricity all increase in resistance as their temperatures rise. Pure metal shows this effect more strongly than alloys. However, pure metals generally have a better conductivity than alloys at room temperature. The conductivity of metals and metal alloys improves as the temperature falls.
Conversely, non-metallic materials used for insulators tend to offer a lower resistance to the passage of electrons, and so become poorer insulators, as their temperatures rise. Glass, for example, is an excellent insulator at room temperature, but becomes a conductor if raised to red heat.
Magnetic Properties
The magnetic properties of a material are those which determine the ability of material to be suitable for a particular magnetic Application.
All matter exhibits magnetic properties when placed in an external magnetic field. Even substances like copper and aluminum that are not normally thought of as having magnetic properties are affected by the presence of a magnetic field such as that produced by either pole of a bar magnet. Depending on whether there is an attraction or repulsion by the pole of a magnet, matter is classified as being either paramagnetic or diamagnetic, respectively.
Electrical Conductivity vs Thermal Conductivity
This chart shows the attractive nature of alumina. Most. Materials have a strong relationship between electrical and thermal conductivity. Ceramics like alumina are unusual in that they can have excellent thermal conductivity - but provide high electrical insulation.
Aluminum oxide is a chemical compound of aluminum and oxygen with the chemical formula Al2 O3 It is commonly called alumina
Electrical and Thermal conductivity of Fiber materials
Defines the Metals
A metal is a material (an element, compound, or alloy) that is typically hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable that is, they can be hammered or pressed permanently out of shape without breaking or cracking as well as fusible (able to be fused or melted) and ductile (able to be drawn out into a thin wire). About 91 of the 118 Clements in the periodic table are metals, the others are nonmetals or metalloids. Some elements appear in both metallic and non-metallic forms.
There are two types of metal, ferrous metal and non-ferrous metal. Ferrous metal contains iron, Non-ferrous metal does not contain iron. A combination of two or more metals is called an alloy. An alloy is produced to have properties which could not be achieved with the individual substances.
Examples iron (Fe), copper (Cu), aluminum (Al), nickel (Ni), titanium (Ti). Nonmetallic elements such as carbon (C), nitrogen (N) and oxygen (0) may also be contained in metallic materials. Metals usually are good conductors of heat and electricity. Metals have a crystalline structure in which the atoms are arranged in an orderly manner. In chemistry, a metal is an element that readily forms positive ions (captions) and has metallic bonds. Metals are sometimes described as a lattice of positive ions surrounded by a cloud of delocalized electrons. A modern definition of metals is that they have overlapping conduction bands and valence bands in their electronic structure.
The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. On the periodic table, a diagonal line drawn from boron (B) to polonium (Po) separates the metals from the nonmetals, Most elements on this line are metalloids, sometimes called semi-metals; elements to the lower left are metals; elements to the upper right are nonmetals.
Defines the Ceramics
They are generally compounds between metallic and nonmetallic elements chemically bonded together and include such compounds as oxides, nitrides, and carbides. Ceramic materials can be crystalline, non-crystalline, or mixtures of both.
Typically they have high hardness and high-temperature strength but they tend to have mechanical brittleness. They are usually insulating and resistant to high temperatures and harsh environments.
Ceramics can be divided into two classes: traditional and advanced.
Traditional ceramics include clay products, silicate glass and cement;
Advanced ceramics consist of carbides (SiC), pure oxides (A1203), nitrides (Si3N4), non silicate glasses and many others.
Ceramics are used in a wide range of technologies such as refractories, spark plugs, dielectrics in capacitors, sensors, abrasives, magnetic recording media, etc. The space shuttle makes use of -25,000 reusable, lightweight, highly porous ceramic tiles that protect the aluminum frame from the heat generated during re-entry into the Earth's atmosphere.
Polymer
There are many different polymeric materials that are familiar to us and find a wide variety of applications; in fact, one way of classifying them is according to their end use. Within this scheme the various polymer types include plastics, elastomers (or rubbers), fibers, coatings, adhesives, foams, and films.
Plastics:
Possibly the largest number of different polymeric materials come under the plastic classification. Plastics are materials that have some structural rigidity under load, and are used in general-purpose applications. Plastic materials may be either thermoplastic or thermosetting.
The response of a polymer to mechanical forces at elevated temperatures is related to its dominant molecular structure. In fact, one classification scheme for these materials is according to behavior with rising temperature. Thermoplastics (or thermoplastic polymers) and thermosets (or thermosetting polymers) are the two subdivisions.
This polymerization can create two varieties
of plastics: thermoplastics and thermosetting plastics. Thermoplastics soften under heat and harden with cooling: thermosetting plastics harden after the first heating and form links with other plastic molecules that never soften again.
The material used for injecting into the plastic injection molds is derived from two different basic plastics: thermoplastic and thermosetting plastic. Most familiar plastic items are made from thermoplastics because these meltable plastics can be shaped and reshaped easily.
Thermoplastic
A thermoplastic (sometimes written as thermo plastic) is a type of plastic made from polymer resins that becomes a homogenized liquid when heated and hard when cooled. When frozen, however, a thermoplastic becomes glass-like and subject to fracture. These characteristics, which lend the material its name, are reversible. That is, it can be reheated, reshaped, and frozen repeatedly. This quality also makes thermoplastics recyclable.
So Thermoplastics soften when heated (and eventually liquefy) and harden when cooled-processes that are totally reversible and may be repeated. On a molecular level, as the temperature is raised, secondary bonding forces are diminished (by increased molecular motion) so that the relative movement of adjacent chains is facilitated when a stress is applied. Irreversible degradation results when a molten ther plastic polymer is raised to too high a temperature. In addition, thermoplastics are relatively soft. Most linear polymers and those having some branched structures with flexible chains are thermoplastic.
There are dozens of kinds of thermoplastics, with each type varying in crystalline organization and density. Some types that are commonly produced today are polyurethane, polypropylene, polycarbonate, and acrylic.
Properties of thermoplastic materials are:
It may melt before passing to a gaseous state.
Allow plastic deformation when it is heated. They are soluble in certain solvents.
Swell in the presence of certain solvents.
Good resistance to creep.
Examples and applications of thermoplastic plastic materials:
High pressure polyethylene as applied to rigid material covered with electrical machines, tubes, etc....
Low pressure polyethylene elastic material used for insulation of electrical cables, etc...
Polystyrene applied for electrical insulation, handles of tools... . Polyamide used for making ropes, belts, etc...
PVC or polyvinyl chloride for the manufacture of insulation materials, pipes, containers, etc...
Polyethylene is likely the most commonly encountered thermoplastic and is used to make shampoo bottles, plastic grocery bags, and even bullet proof vests.
These materials are normally fabricated by the simultaneous application of heat and pressure (see Section 15.22). Examples of common thermoplastic polymers include polyethylene, polystyrene, poly(ethylene terephthalate), and poly(vinyl chloride).
Thermosetting
Thermosetting polymers are network polymers. They become permanently hard during their formation and do not soften upon heating Network polymers have covalent crosslinks between adjacent molecular chains. During heat treatments, these bonds anchor the chains together to resist the vibrational and rotational chain motions thigh temperatures. Thus, the materials do not soften when heated, Crosslinking is usually extensive, in that 10% to 50% of the chain repeat units are crosslinked. Only heating to excessive temperatures will cause severance of these crosslink bonds and polymer degradation. Thermoset polymers are generally harder and stronger than thermoplastics and have better dimensional stability. Most of the crosslinked and network polymers, which include vulcanized rubbers, epoxies, phenolics, and some polyester resins, are thermosetting.
Thermoset materials are those materials that are made polymers joined together by chemical bonds, acquiring a highly cross-linked polymer structure.
The highly crosslinked structure produced by chemical bonds in thermoset materials, is directly responsible for the high mechanical and physical strength (high strength to support high stress or load, temperature...) compared with thermoplastics or elastomers materials.
Thermoset material properties:
You cannot melt.
Generally do not swell in the presence of certain solvents
They are insoluble.
High resistance to creep
Examples and applications of thermoset plastic materials:
Epoxy resins used as coating materials, caulks, manufacture of insulating materials, etc...
Phenolic resins- tool handles, billiard balls, sprockets, insulation, etc....
Unsaturated polyester resins - manufacture of plastics reinforced fiberglass commonly known as polyester, fillers, etc...
Wood
Wood composites fall into 3 categories
Laminated Boards
Plywood is the most commonly known Laminated Board. It consists of thin layers of wood bonded together. To prevent warping and to give strength these boards are layered i such a way that their grains run 90° to each other.
Particle Boards
Particle Board is made from recycled materials such as sawdust or shavings that have been bonded together to form Chip Board. This Chip Board is used in the manufacturer of Kitchen Units
Fiber Boards
Fibre Board is made from compressed fibres of differing length that have been bonded together. They include both Hardboards and Medium Density Fibreboard (MDF)
Glass
This is a hardwearing, abrasion-resistant material with excellent weathering properties. It is used for electrical insulators, laboratory equipment, optical components in measuring instruments, in the form of fibers, is used to reinforce plastics. It is made by melting together the naturally occurring materials silica (sand), limestone (calcium carbonate) and soda (sodium carbonate).
Factors affecting materials properties:
The following are the more important factors which can be influence the properties and performance of engineering materials.
Heat treatment
This is the controlled heating and cooling of metals to change their properties to improve their performance or to facilitate processing. An example - heat treatment is the hardening of a piece of high carbon steel rod. If it is heated to dull red heat and plunged into cold water to cool it rapidly (quenching), it will become hard and brittle. If it is again heated to dull red heat but allowed to cold y slowly it will become softer and less brittle (more tough). In this condition it is said to be be annealed.
After the heat treatment happened on the material it will be in its best condition for flow forming. During flow forming (working) the grains will be distorted and this will result in most metals becoming work hardened if flow formed at room temperature. To remove any locked in stresses resulting from the forming operations and to prepare the material for machining, the material has to be normalized.
Processing
Hot and cold working process will be referred to understand what is meant by terms hot and cold working as applied to metals. Figure shows examples of hot and cold working.
Figure 8. Examples of (a) hot-working and (b) cold-working process.
Metal is hot worked or cold worked depending upon the temperature at which it is flow formed to shape. These temperatures are not easy to define, for instance, lead hot works at room temperature and can be beaten into complex shapes without cracking, but steel does not hot work until it is red hot.
When metal are examined under the microscope it can be seen that they consist of very small grains. When most metals are bent or worked at room temperature (cold worked) these grains become distorted and the metal becomes hard and brittle.
When metals are hot worked the crystals are also distorted. however, they reform instantly into normal crystals because the process temperature is above the temperature of recrystallization for the metal being used and work hardening does not occur, this cold working is the flow forming of metals below the temperature the recrystallization, whilst hot working is the flow forming of metals above the temperature of recrystallization.
Environmental reactions
The properties of materials can also be effected by reaction with environment in which they are used.
For example:
Resting of steel
Unless steel structures are regularly maintained by rest neutralization and painting process, resting will occur. The rest will eat into the steel, reduce its thickness and, therefore, its strength. In extreme cases an entire structure made from steel may be eaten away.
Dezincification of brass
Brass is an alloy of copper and zine and when brass is exposed to a marine environment for a long time, the salt in the sea water pray react with the zinc content of the brass so as remove it and leave it behind on spongy, porous mass of copper. This obviously weakness the material which fails under normal working conditions.
Degradation of plastic
Many plastic degrade and become weak and brittle when exposed to the ultraviolet content of sunlight. Special dyestuffs have to be incorporated into the plastic to filter out these harmful rays.
Ageing
Ageing of materials or products implies changes of the original state, but it does not necessarily only comprise deterioration or degradation. Ageing can also mean formation of new substances and stabilization. In some cases this effect is desirable. Ageing of incineration ash and slag leads to carbonation [7, 8]. With respect to organic matter humic substances are built up resulting in a stable organic fraction with low turnover rates. These natural processes that come along with material ageing were adopted for technical applications, e.g. humification in the course of composting.
Alloys
Pure Metals have the following physical properties.
High Density.
High Melting & Boiling Points Good Conductors of Heat Electricity.
Malleable.
Ductile.
Lustrous.
So weakness of pure metals are weak & soft due to their ductility and malleability.
ALLOYS DEFINITION:
Alloy is a mixtures of two or more elements with a certain fixed composition in which the major component is a metal.
Characteristics of alloy are: (Stronger, Harder, Resistant to corrosion, Have a better finish & Lustrous) Harder than their components
Less Ductile Less Malleable, so hardness of Gold is increased by addition of Copper to it Melting Point of alloys is always less than the Melting Points of constituent’s metals Other properties like reactivity towards oxygen & moisture, colour etc depends upon constituents
Bronze -90% copper 10% tin-Hard and strong" Does not corrode easily Has shiny surfaces to build statues and monuments in the making swards, medals and artistic materials
Brass 70% copper-30% zinc Harder than copper in the making of musical instruments and kitchenware
Steel ~ 99% iron~1% carbon ~ Hard and strong in the construction of building and bridges in the building of cars and railway tracks
Stainless steel -74% iron ~8% carbon~18% chromium “shiny strong does not rust to make surgical instruments
Duralumin 93% aluminum - 3% copper ~ 3% magnesium" 1% manganese ~ light strong to make the body of aero planes and bullet trains
Pewter 96% tin ~3% copper 1% antimony "luster shiny strong in the making of souvenirs
Uses of Alloys
To Modify Chemical Reactivity: When sodium is used as reducing agent, it is too reactive to be used Na+ Hg → Sodium Amalgam
To increase Hardness: Hardness of gold is increased when Cu is added Zn + Cu → Cu becomes harder (Brass)
To Increase Tensile Strength: Nicely, [An alloy of Ni (1%), Cu (4%), and Al (95%)] has greater tensile strength
To Lower The Melting Point: Solder Metal which is an alloy of Sn (30 %) , Pb ( 70 %), has very low Melting Point as compared to Sn & Pb
To Modify Colour: Alumni Bronze, (An alloy of Cu & Al) has beautiful Golden colour To Resist Corrosion: Fe gets rusted and corroded its corrosion takes place with time but Stainless Steel, alloy of Fe & C is not rusted. | Fe (98%), C(2%)]
