In this article, you will learn in details about the Mechanical Properties of Materials and Metals.
Table of Contents
Mechanical Properties of Materials.
A mechanical property deals with the behavior of materials or metals when they are subjected to the external forces or loads. It is the characteristic that indicates the variations taking place in the metal.
These mechanical properties are considered while designing machine components. The component will perform well during its use only when it is designed by considering all mechanical properties.
The behavior of materials under external loads is called Mechanical Properties of Materials.
The most important and useful mechanical properties are;
1. Stress.
2. Strain.
3. Elongation.
4. Contraction.
5. Elasticity.
6. Plasticity.
7. Strength.
8. Impact strength.
9. Yield strength.
10. Stiffness.
11. Toughness.
12. Hardness.
13. Brittleness.
14. Malleability.
15. Ductility.
16. Fatigue.
17. Creep.
You’ll learn all of the above mechanical properties of metals and materials here in details.
1. Strength.
It is the mechanical property of a metal, which provides resistance to an external force or it is the capacity or ability to withstand various loads without deformation or breaking.
Hence, it is the highest resistance offered by the material when it is subjected to an external load. Stronger the material, greater is the load it can withstand.
In the case of metals, strength is very important, because the metals should tolerate heavy loads. It means that metals should not be induced with heavy stress and deform.
If the metals have high strength, they can withstand various loads.
The various loads which may act on the metal components of the machine tool are;
1. Tensile,
2. Compressive,
3. Shear,
4. Bending,
5. Torsion etc.,
and their respective strengths include;
1. Tensile strength,
2. Compressive strength,
3. Shear strength.
4. Bending strength,
5. Torsion strength, etc.
Some metals and their alloys possess high strength per unit mass, making them useful materials for carrying heavy loads or resisting any damages due to impact loads.
Depending upon the type of load applied the strength can be tensile, compressive, shear or torsional. The material can be loaded by means of heating, internal structure, loading type, etc.
The maximum stress that any material will withstand before destruction is called its ultimate strength.
2. Impact Strength.
It is that property of the metal which gives its ability to withstand shock or impact or sudden loads.
When impact load is applied within the elastic limit of the material, that energy is absorbed by the material and given out when the load is removed, as in case of spring materials.
This property within an elastic limit is known as resilience.
However, the impact strength is its load withstanding capacity up to its rupture. Some times the impact load leads to failure of the metal component.
The impact loads may exist in shear, compressive, or tensile. Impact strength can be measured by Charpy or Izod test.
The Charpy test measures the ability of a metal to withstand the applied impact load, while, Izod test measures the load required to rupture the metal component.
3. Elasticity.
The property of metal and its ability to return to its shape and size after removal of load or to regain its initial position or shape and size when the applied load is removed is called elasticity.
Most of the components are designed with a suitable elasticity; otherwise, the machine components will be deformed when it is subjected to loads.
Most of the metals have better elasticity such as heat treated springs and coils made up of steel, copper, aluminum, etc.
However, some of the metals are not elastic; they have properties like brittleness and hardness. Elasticity is a tensile property of its material.
The greatest stress that a material can endure without taking up some permanent deformation is called the elastic limit.
4. Stiffness (Rigidity).
The resistance of a material to deflection is called stiffness or rigidity, or it is the property of a metal due to which it resists deformation when it is within the elastic limit.
The metals having higher stiffness can deform very less or are not deformed at all.
To understand stiffness the modulus of elasticity or young’s modulus is to be measured for the respective metal because it is the measure of stiffness for tensile and compressive loads.
Modulus of rigidity is used for shear loads and bulk modulus for volumetric deformation.
Steel is stiffer or more rigid than aluminum.
Stiffness is measured with Young’s modulus (E). Higher the value of Young’s modulus, stiffer is the material.
5. Plasticity.
It is the property of a metal that gives the ability to deform non-elastically; without fracture, they do not regain their original shape and size when the applied load is removed.
In this case, the material undergoes some degree of permanent deformation without failure. Plasticity is the reverse of elasticity.
In the cold and hot working of metals, the metal undergoes permanent deformation even when the process is completed.
For example, steel will be deformed when red-hot, and it does not regain its original shape and size. Similarly, lead, clay, etc., would be plastic at room temperature.
Plasticity is useful in several mechanical processes like forming, shaping, extruding, and many other hot and cold working processes.
In general, plasticity increases with increasing temperature and is a favorable property of material for secondary forming processes.
Due to these properties, various metal can be transformed into different products of required shape and size. This conversion into desired shape and size is effected either by the application of pressure, heat, or both.
6. Hardness.
The hardness of a material is the measurement of plastic deformation, and it is the resistance to any plastic deformation. Hardness indicates the strength of the material.
It is the ability of a material to resist scratching, abrasion, indentation, or penetration.
It is directly proportional to tensile strength and is measured in special hardness testing machines by measuring the resistance of the material against the penetration of an indentor of special shape and material under a given load.
The different scales of hardness are Brinell hardness, Rockwell hardness, Vicker’s hardness, etc.
The hardness of a metal does not directly relate to the harden-ability of the metal. Harden-ability is indicative of the degree of hardness that the metal can acquire through the hardening process. i.e., heating or quenching.
7. Ductility.
It is the property of material or metal that represents plastic deformation under tensile load, or it enables it to be drawn into wires or elongated. Without rupture under tensile load.
The metals used for machine tools production must have considerable ductility; it is the opposite of brittleness.
Various metal such as steel, steel alloys, mild steel, copper, aluminum, tin, zinc, etc., are examples of good ductile materials.
Gold, silver, copper, aluminum, etc., can be drawn by extrusion or by pulling through a hole in a die due to the ductile property.
The ductility decreases with increase in temperature. The percent elongation and the reduction in area in tension are often used as empirical measures of ductility.
8. Malleability.
It is the property of material or metal that represents plastic deformation under compressive load, or it is the property of a metal which enables it to roll into thin sheets or plates.
Metals used for manufacturing the machine tool components must have sufficient malleability because of the metal size and shape changes during the manufacturing of the components according to design.
Various metals, such as copper, aluminum, gold, wrought iron, steel alloys, and soft steel, etc., are examples of good malleable materials.
9. Toughness.
It is the ability to absorb energy up to failure or fracture, or toughness is the ability of a material to resist any deformations due to bending, twisting, torsion, etc.
It is measured by an impact test.
Steel and steel alloys such as manganese steel, wrought iron, mild steel, etc., usually, all ductile materials are tough materials.
10. Brittleness.
It is the property of a material and indicates fracture without appreciable deformation, and is opposite to toughness and ductility.
The brittle material fails or breaks very easily, even with the application of a very small load.
Cast iron, glass, etc., are brittle materials used in the engineering applications.
The machine tool components must have zero or very less brittleness; otherwise, they will break or fail.
11. Fatigue.
Fatigue represents the tendency to fracture under cyclic loading, or it is the inability to withstand repeated and/or continuous application and removal of loads or cyclic loads.
The fatigue is the prolonged effect of repeated straining due to application and removal of stress, by which material breaks or fractures.
The machine tool components must withstand such a fatigue loading, and this must be considered while designing of machine tool components, high-speed Aero engines, and turbines where they are required to give long services under cyclic loads.
12. Creep.
Creep represents slow and progressive deformation with time at constant stress, or it is the failure or deformation of the material under constant stress at high temperature over a period of time.
In the case of belt drives, I.C engines, etc., the material is subjected to constant pressure at high temperature.
Under these conditions, the material would slowly and progressively deform over the period of time and finally fails.
Amorphous materials like rubber belts and materials made of plastic are sensitive to creep.
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