The knowledge of physical properties of materials is a must for the selection of materials for a particular application. There are different materials that are required for any engineering work to be carried out. These materials are collectively called Engineering materials. Almost all materials that we look around like metals, non-metals, polymers, different chemicals, fibbers, etc. constitute Engineering materials.
Every Engineering material has a set of properties that make them suitable for one work or the other. These properties are classified as – physical properties and chemical properties of materials. Here, we will discuss the physical properties of an engineering material in detail.
The physical properties of a material can be defined as its inherent property that can be observed without altering the identity of the material. Proper knowledge and study of these properties help us choose a material for a specific purpose. E.g. Copper is chosen to make electrical conductors and not paper because copper is a good conductor of electricity as compared to paper which is a bad conductor of electricity. So, conductivity is the physical property based on which the comparison has been drawn out.
Types of Physical Properties of Engineering Materials
Physical properties are of two types: Intensive properties and Extensive properties.
Intensive properties are the properties that are independent of the volume or size of the engineering material. These properties are also known as Bulk properties. The followings are the intensive physical properties of the materials.
- Melting Point
- Boiling Point
- Thermal Conductivity
- Refractive Index
- Specific Heat Capacity
- Thermal Expansion Coefficient
- Magnetic susceptibility
Now, we will discuss each intensive physical property of the material in detail.
The force exerted per square unit area on the material’s surface that is perpendicular to the direction in which the force is exerted is known as Pressure. It is an important physical property of the material. It is given as;
Where P is the pressure, F is the applied force and A is the surface area of the material. The pressure is measured in kg/metre2.
Temperature is the quantitative expression of the relative hotness or coldness of a material with respect to its surrounding. It is the average kinetic energy of the molecules of a substance. It is measured in Fahrenheit, Celsius, or Kelvin scale.
The temperature of a material doesn’t depend on the size or volume of the material. Whether there is 100 kg of ice or only 100 grams, the ice melts at 0 deg. C irrespective of the amount.
The melting point of a material is a physical property that indicates a specific temperature at which a solid material converts into liquid. Depending on the application, certain impurities can be added to the material to increase or decrease the melting point. Impurities introduce defects or by introducing atoms that can affect the melting process of a material.
The boiling point of a material is a specific temperature at which a liquid turns into a gas. Just like in the case of melting point, impurities can be added to a material to increase or decrease its boiling point.
Density provides information about the concentration of particles and molecules or how tightly they are packed within a given volume. It is defined as the mass per unit volume of a material. It is given by;
Where ρ is the density, m is the mass and V is the volume of the material. Thus density is measured in kg/m3.
The ductility of a material is defined as the ability of the material to be drawn into a thin wire. The ductility of a material indicates the degree to which a material can sustain plastic deformation under tensile stress before failure.
The malleability of material is its ability to be beaten down into thin sheets by hammering, forging, etc.
Conductivity is an important physical property of a material that shows the availability of free electrons in the material. The conductivity of a material is the ability of the material to conduct electricity when a certain voltage is applied across it. Materials having free electrons like metals are good conductors of electricity as compared to insulators which have no free electrons in the outer shell of their atomic structure.
Materials like Silicon, Germanium, Gallium Arsenide, etc. have conductivity between the conductors and the insulators. Hence these are known as semiconductor materials and are used for making semiconductor components.
The toughness of a material is its ability to resist a fracture or rupture in its shape. Toughness is also defined as the amount of energy that a material can absorb before rupturing. It is the combination of strength and ductility of a material. Diamond is the toughest known material on earth.
The thermal conductivity of a material is a physical property that indicates its ability to transfer heat. Thermal conductivity defines how efficiently a material can conduct heat from one point to the other. Metals have high thermal conductivity while insulators are poor thermal conductors. Thus metals are used in heat transfer applications whereas insulating materials are used for insulating a hot material so that it could be handled. It also conserves heat by shielding the hot body.
The refractive index is the property of the material that shows how light propagates through a material. This property depends on the characteristics of the material and does not depend on the size or amount of the material. It is an intensive property because it characterizes the material itself and is not affected by the size or amount of the material.
Specific Heat Capacity
Specific heat of a material is defined as The amount of heat required to raise the temperature of the unit mass of material by 1oC is called specific heat of the material. It is denoted by ‘S’.
m is the mass of material in Kg.
Q is the amount of heat given to material in Joule.
Δt is a rise in temperature.
The unit of specific heat S in the SI system is Joule/Kg oC.
Thermal Expansion Coefficient
The coefficient of thermal expansion shows the expansion of material with an increase in temperature. There are three types of thermal expansion coefficients. They are-
Coefficient of Linear Expansion
The change in the length of the material with an increase in temperature is called the coefficient of linear expansion. It is denoted by the letter “αL”
The Unit of αL is per oC.
Coefficient of Area Thermal Expansion
The change in the area of an object because of a change in temperature is called the “Coefficient of Area thermal expansion”. It is denoted by “αA”.
The Unit of αA is per oC.
Coefficient of Volume Thermal Expansion
The change in the volume of the material with a change in the temperature is called the coefficient of volume thermal expansion. It is expressed by the letter “αV”
The unit of αV is per oC.
The degree to which a material can be magnetized in the presence of an external magnetic field is called magnetic susceptibility. It does not depend on the amount of material.
The extensive properties of a material are the physical properties of the materials that depend on the amount of matter present in the material. Unlike the intensive properties, the size and volume of the material determine its extensive properties. The followings are the extensive properties of a material.
- Heat Capacity
- Electric Charge
We will now discuss the extensive physical properties of the material in detail.
Mass is a physical property of a material that is defined as the amount of matter present within a material. The mass of material remains constant anywhere. The acceleration due to gravity changes from one place to the other and its product with the mass gives us the weight of the material which is a variable quantity.
Length is the measurement of the size or extent of material in one dimension.
The volume is a physical property of the material that shows the amount of space occupied by a material in a 3-Dimensional space. It is an extensive property as it depends on the amount of material. Similarly, the length, breadth, area, and height of a material are its extensive properties.
The heat capacity of a material is the amount of heat required to raise the temperature of the material by a certain unit. It is defined as the ratio of heat absorbed by a material to its temperature change.
Heat Capacity is measured in Calories/deg. C.
The entropy is a physical property of the material. The entropy of a material is defined as the disorderness or randomness of its matter. It is the measure of the thermal energy of the material per unit temperature that is unavailable for doing some useful work as any useful work requires ordered molecular motion.
Electric charge is a physical property of a material that causes it to experience a force when placed in an electromagnetic field. The Net Electric charge present on the given material is its extensive property as it depends on the amount of substance.
The product of an object’s mass and velocity is called the momentum of the material. The momentum will be more if there is more amount of material. Thus, the physical property of the material- momentum – depends on the size of the material.
The property of the material allows it to have energy in various forms like thermal, chemical, or mechanical energy.
These are some of the important physical properties of Engineering materials, classified as intensive and extensive, that help us to compare and choose a suitable material that can give the desired result in an application.