Mechanical Properties of Engineering Materials

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Mechanical Properties of Engineering Metals

The mechanical properties of engineering materials has an great importance in design of machines, tool design and structures. The important mechanical properties of the metals are strength, elasticity, stiffness, plasticity, ductility, malleability, toughness, hardness, brittleness, formability, castability and weldability. With the help of stress-strain diagram, these properties can be well understood. Few important mechanical properties are discussed below :
1. Strength: Strength is defined as the ability of the material to resist the externally applied forces with breakdown or yielding. The internal resistance offered by a material to an externally applied force is called stress.
The capacity of bearing the load by a metal and to withstand a destruction under the action of external load is known as Strength.
Stronger the material, greater the load it can withstand. This property of material therefore determines the ability to withstand stress without failure. Strength varies according to the type of the loading. It is always possible to access tensile, compressive, shearing and torsional strength.
The max stress that any material can withstand before destruction is called ultimate strength.
2. Elasticity: It is the property of a material to regain its original shape after deformation when the external forces are removed. It can also be referred as the power of the material to come back to its original position after deformation when stress or load is removed. It is also known as the tensile property of the material.
3. Stiffness: It is the ability of the material to resist the deformation under the stress. The resistance of material to elastic deformation of deflection is called stiffness or rigidity.
A material that suffers very low or slight deformation under load, has high stiffness. For instance, suspended beams of steel and aluminium may both be strong enough to carry the required load but aluminium beam will sag or deflect further. This means, steel beam is more rigid than aluminium beam.
4. Plasticity: It is the mechanical property of the material which retains the deformation produced under the load permanently. This property of material is required in forging, in stamping images on coins and in ornamental work. It is the ability or tendency of the material to undergo some degree of permanent deformation without its rupture or failure. Plastic deformation takes place only after elastic range of the material has been exceeded. Such property of material is important in forging, stamping, shaping, extruding and many other hot and cold working processes. This property generally increases with increase in its temperature.
5. Ductility: Ductility is termed as the property of the material enabling it to be drawn into wire with the application of tensile load. Ductile material must be strong and plastic. The ductility is usually measured by the terms, percentage elongation and percent reduction in area which is often used as empirical measures of ductility.
6. Malleability: Malleability is the ability of the material to be flattened it into thin sheets under application of heavy forces without cracking by hot or cold working process. It is special case of ductility which permits material to be rolled or hammered into thin sheets. A malleable material should be plastic but it is not essential to be strong.
7. Hardness: Hardness is the ability of the metal to cut another metal. A harder metal can always cut or put impression to the softer materials by virtue of its hardness. It is very important property of the metals and has high a wide variety of meanings. It embrasses many different properties such as resistance to wear, scratching, deformation and machinability.
8. Brittleness: It is the property of the material exactly opposite to ductility. It is the property of the breaking of material with little permanent distortion. The materials having less than 5% elongation under loading behavior are said to be brittle material. Brittle materials when subjected to tensile load snap off without giving any sensible elongation.
9. Formability: It is the property of the metals which denotes ease in its forming in to various shapes and sizes. The different factors that affect formability are crystal structure of metal, grain size of metal, hot and cold metal working, alloying element present in its parent metal. Metals with small grain size are suitable for shallow forming while metals with size are suitable for heavy forming. Hot working increases formability. Low carbon steel possesses good formability.
10. Castability: Castability is defined as the property of the metal which indicates the ease with it can be casted into different shapes and sizes.
11. Weldability: It is the property of the metal which indicates the two similar or dissimilar metals are joined together by fusion with or without application of pressure and with or without use of filler metal efficiently. Metals having weldability is descending order are iron, steel, cast steel and stainless steel.
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Sujit Kadus

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