Engineering Materials

It is a science that deals with the association among the structure and the properties of the materials.

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Properties of materials:

Properties of the materials are divided in to six categories. They are

  • Decorative
  • Electrical
  • Magnetic
  • Mechanical
  • Optical
  • Thermal

Every material possesses a structure, relevant properties. They depend upon the giving out and govern the performance.

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Normal materials possess strength which is limited to ductility.

During that condition reasonable compromise among the two or more properties are essential.

During provision process second selection consideration is any way of material properties.

Classification of the materials:

Based upon the structure and the atomic bonds the engineering materials are divided. They are

  • Metal
  • Non metals
  • Due to combination of the materials

Engineering Materials

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Metals:

Metals are further classified into two types they are

  1. Ferrous
  2. non-ferrous

Ferrous:

Ferrous are alloys or metals, which contain a high amount of iron elements. These are very strong materials, used for the application where high strength is required and at low cost. Ferrous metals are used in the large buildings, locomotives, bridge buildings and railway lines.

Ferrous are divided in to two types they are:

  1. Steels
  2. Cast irons

Steels:

Steels are divided in to two types they are:

  • Alloy steels
  • Plain Carbon steel

Cast iron:

Cast iron is divided in to four types they are:

  • Gray cast iron
  • White cast iron
  • Malleable cast iron
  • Ductile cast iron

Non – ferrous:

Non – ferrous metals are pure metals which are rarely used as structural materials, and they lack mechanical strength. The non – ferrous metals are used where their special properties such as electrical conductivity, resistance and thermal conductivity are required. Aluminum and copper are used as electrical conductors, along with sheet lead and sheet zinc that are used as roofing materials.

Non – ferrous metals are divided in to several types they are

  1. Aluminum
  2. Cu
  3. Mg
  4. W
  5. Zinc
  6. Lead
  7. Nickel

Non – metals:

Nonmetals are divided in to two types they are

  • Ceramics
  • Organic polymers

Combination of the materials

  1. Composite
  2. alloys

Composites

  1. Ceramic polymers
  2. Polymer cement concert
  3. Carbon reinforced
  4. Metal ceramic
  5. Metal reinforced metal
  6. Whisker reinforced metal

Alloys:

Alloys are divided in to two type’s they are

  1. Non-ferrous alloys
  2. Ferrous alloys

Factors affecting material properties:

Heat treatment:

Heat treatment is used to control heating and cooling of the metals to change the properties and also to improve the performance or to enable processing.

For example:

Heat treatment is the method of hardening of a piece of hydrocarbon steel rod. After heating the rod when it turns to red heat, and later rushed into the cold water it undergoes the process rapidly. Later, it becomes hard and brittle. The material is again heated to dull red, but it allows the rod to cold very slowly, which then becomes very softer and less brittle. This process is known as the annealed. After the heat treatment done to the material, it is considered to be in its best condition for flow forming process. During the time of flow forming the grains are deformed, which results in most metals flattering work hardened if flow formed at room temperature. This is to remove the stress from the forming operations and prepare the material for machining process, and then material is made to normalize.

Processing:

Hot and cold working process is applied to the metals. The shape of the metal is obtained based upon the cold working process or hot working process. The temperature is not easy to explain. Hot works are done at the room temperatures and can be compressed into difficult shapes. The steel is not made to do hot work until it is red hot. When the metal is tested under the microscope then it contains very small grains. When the metals are worked or bend at the room temperature, at that instance the grains deform, later the metal becomes very hard and brittle. Hot process is applied to the metals at that instance crystals are also distorted. They reform is done instantly into the standard crystals, because the developed temperature is directly above the temperature of recrystallization for the metal being used. The cold working process is the flow forming of metals below the temperature where the recrystallization, on the other hand the hot working process is the flow forming metals above the temperature of recrystallization.

Environmental reactions:

The properties of the materials can also be achieved by reaction with surroundings in which they are used.

Some examples are:

Resting of steel

Dezincification

Degradation of plastic

General properties of engineering materials:

Properties of materials play a key role. The properties are classified into several types they are:

Physical properties of materials:

The physical properties of the materials deals with some of the properties like temperature, melting, electrical conductivity, density, thermal conductivity, magnetic properties, corrosion resistance etc.

In the following properties some of them are considered to be more important, they are:

Density:

  • For material density is known as mass per unit volume. The units are kg/m^3
  • At 4^o \: C the density of the material compared with the density of water is known as relative density.

Density = \frac{mass(m)}{volume(V)}  and

Relative density =\frac{Density\: \: of \:\:the \:\:\:material}{Density\:\: of\: \: pure\: \: water\: \: at\: \: 4^0 C}  

Electrical Conductivity:

Copper wire must be selected for the electrode or core of the cable; this is because the Copper acts as a very good electrical conductivity. The wire conductor material is provided by the insulation, for which a plastic material like polymerized has been chosen. This material has been select as it is a bad conductor of electricity; very few electrons can pass through it. Insulators are very bad conductors of electricity. When pure metals compare with alloys they are stronger. At room temperatures the pure metals have better conductivity than alloys. The temperature fall is improved with the conductivity of metals and metal alloys. Equally non – metallic materials used for insulators, as they offer a lower resistance to pass the electrons, and become poor insulators, as the temperature rises. For example glass is an excellent insulator.

Melting temperature of material:

The recrystallization temperature and melting temperature have a great effect on the materials and the properties of the alloy material.

Semi-Conductors:

Semi-conductor materials lie between the conductors and isolators materials. Depending upon the temperature, Semi-conductors are classified as good conductors are bad conductors. If there is increase in the temperature in small level, then one can observe the rapidly increase of conductivity of semiconductor materials. The electronic thermometer and the semi-conductors are used as temperature sensors. Semi-conductors have the capabilities, for which during the process of manufacturing the conductor’s properties are to be changed. Silicon and germanium are the examples of semi – conductors. In electronic industry, the conductors are extensively used in the manufacturing of solid devices such as integrated circuits, transistors, diodes and thermistors.

Thermal conductivity:

Thermal conductivity is the ability of the material to transmit heat energy by conduction.

For example tie up a soldering rod to the tip, which is attached to a wooden base.

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The tip is made up of copper, as it is a good conductor of heat. It allows storing the heat energy and easily moves down to the tip, and to the work piece being soldered. Due to the low thermal conductivity the wooden handle remains cool and resists the flow of the heat energy.

Fusibility:

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By applying the fusibility the metals are melted. In the figure it shows that by applying the heat the metals are melted automatically, and it has high fusibility. The materials that melt at high temperature are called as refractory materials. Polystyrene must acts as a thermal insulator and they considered to have low melting point.

Reluctance:

Some materials are good or bad conductors of electricity, and some materials are good or bad conductors of magnetism. The resistance offered by the magnetic circuit is known as the reluctance. The conductors which have good magnetic nature are low reluctance. Ferromagnetic materials are made up of steel and iron, which are also associated with the alloying elements like nickel and cobalt. The remaining materials are non – magnetic, as they offer a high reluctance to the magnetic flux field.

Temperature Stability:

Temperature change scan results in a high amount and it shows the effects on the structure and the properties of the material. If there is a change in the temperature then several can take place such as creep. Creep is defined as the gradual extension of a material over a long period of time while the applied load is kept constant. When we consider the plastic materials creep, which is an important factor, and they are considered when the metals works continuously at high temperatures. In gas turbine blades if the creep rate increases then automatically the temperature is to be increased and is vice versa as the temperature lowers.

Mechanical properties:

Mechanical properties consist of tensile strength, toughness, malleability, hardness, Ductility, stiffness, brittle ness, Elasticity, plasticity etc.

Tensile strength

Tensile strength is the ability of the material to withstand the tensile loads without breaking.

Strength:

Strength is the ability of a material to attack the applied forces without fracturing.

Toughness:

Toughness is the ability of the material to withstand bending, or it is an application of shear stresses without fracture. The rubber or many plastic materials do not scatter so they are tough.

Malleability:

It is the capacity of the substance to tolerate deformation under compression without separation or the malleable materials, to allow a useful amount of plastic deformation. This is it undergoes compressive loading before fracture occurs. Such a material is required for manipulation by the process and rolling, forging and rivet heading.

Hardness:

Hardness is the ability of the material to withstand scratching or depression by another hard body; it is an indication of the wear resistance of the material.

Ductility:

Ductility is the capacity of the substances to undergo deformation, under tension without rupture as in wire drawing.

Stiffness:

Stiffness is used to measure the ability of the material, and not to deflect under an applied load.

Brittleness

Brittleness is the property of a material that demonstrates little or no plastic deformation before break when a force is applied. Also it is typically said in the opposite manner to ductility and malleability.

Elasticity:

Elasticity is the ability of a material to deform under load and return to its original shape and size when the load is removed. If it is made from elastic material it will be the same length before and after the load is applied. All materials possess elasticity to some degree and each one of it has its own elastic limits.

Plasticity

Plasticity is the property which is strictly opposite to elasticity; the ductility and malleability are actual cases of plasticity. Plasticity is the state of a material which has been fully loaded beyond its elastic limit so as to cause the material to deform permanently. Under such conditions the material takes a permanent set and will not return to its original size and shape when the load is removed.

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