Mechanical Properties Of Engineering Materials

Mechanical Properties Of Engineering Materials 

Engineering materials play a vital role in this modern age of science and technology. Various kinds of materials are used in industry to meet the requirement of human beings. The selection of a specific  material for a particular use is a very complex process. However, one can simplify the choice if the details about.
1. use parameters.
2. manufacturing process.
3. Functional requirement.
4. Cost considerations 
while selecting materials for engineering purposes, properties such as impact strength, tensile strength, and hardness indicate the suitability for selection but the design engineer will have to make sure that the radiography and other properties of the material are as per the specification . 

1.Strength- The strength of metal is its ability to withstand various forces to which it is subjected during a test or n service, It is usually defined as tensile strength, compressive
strength, proof stress, shear strength, etc. Strength of materials is a general expression for the measure of capacity of resistance possessed by solid masses or pieces of various kinds to any cause tending to produce in them a permanent and disabling change of form or positive fracture. Materials of all kinds owe their strength to the action of the forces residing in and about the molecules of the bodies but mainly to that ones of these known as cohesion: certain modified results of cohesion as toughness or tenacity, hardness, stiffness and elasticity are also important elements, and strength is in relation of the toughness and stiffness combined.

2. Elasticity - A material is said to be perfectly elastic if the whole of the stress produced by a load disappears completely on the removal of the load, the modulus of elasticity of Young's modulus (E) is the proportionally constant between stress and strain for elastic materials. Young;s modulus is the indicative of the property called stiffness; small values of E indicate flexible materials and large value of E reflect stiffness and rigidity. The property of spring back is a function of modulus of elasticity and refers to the extent to which metal springs back when and elastic deforming load is removed. In metal cutting, modulus of elasticity of the cutting tools and tool holder affect their rigidity. Values of modulus of elasticity for same important metal are.

3. Plasticity -Plasticity is the property that enable the formation of permanent deformation in a material. It is reverse of elasticity ; a plastic material will retain exactly the shape it takes under load, even after the load is removed. Gold and lead are the highly plastic materials. Plasticity is used in stamping images on coins and ornamental work.

During plastic deformation there is the displacement of atoms within metallic grains and consequently the shapes of the metallic components change. It is because of this property that certain synthetic materials are given the name "plastics". These materials can be changed into required shape easily.

4. Ductility -  It is the ability of a metal to withstand elongation or bending. Due to this property wires are made by drawing out through a hole. The material shows a considerable amount of plasticity during extension. This is a valuable property in chains, ropes etc. because they do not snap off, while in service, without giving sufficient warning by elongation.

5. Malleability -  This is the property by virtue of which a material may be hammered or rolled into thin sheets without rupture, This property generally increase with the increase of temperature. The  metals in order of their ductility and malleability .

6. Toughness - Toughness is the strength with which the material opposes rupture. It is due to the attraction which the molecules have for each other: giving them power to resist tearing apart.
The area under the stress-strain curve indicates the toughness .Although the engineering stress-strain curve is often used for this the computation, a more realistic result is obtained from a true-stress curve. Toughness is expressed as energy absorbed per unit volume of material participating in absorption or Nm/m³ . This result is obtained by multiplying the ordinate by the abscissa of stress-strain plot.

7. Brittleness - Lack of ductility is brittleness.  When a body breaks easily when subjected to shocks it is said to be brittle.

8. Hardness - Hardness is usually defined as resistance of material to penetration. Hard materials resist scratches or being warn out by friction with another body.
Hardness is primarily a function of the elastic limit of the materials and to a lesser extent a function of the work hardening coefficient. The modulus of elasticity also exerts a slight effect on hardness.
The converse of hardness is know as softness.


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