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Que : 4. Define Hardness, toughness, ductility, brittleness. परिभाषित करे :- हार्डनेस, टफनेस, डक्टिलिटि, ब्रिटलनेस
Answer:

Hardness
Hardness is a very important property of the metals and has a wide variety of meanings. It also embraces many different properties such as resistance to wear, scratching, deformation and machinability etc.
Also, it is the property of a metal, which gives it the ability to resist being permanent, deformed (bent, broken, or have its shape changed) when a load is applied. The greater the hardness of the metal, the greater resistance it has to deformation.
It also means that the ability of a metal to cut another metal. The hardness is usually expressed in numbers which are dependent on the method of making the test.

They are four types of tests are used to determine the hardness of metals, they are
Brinell hardness test,Rockwell hardness test, Vickers hardness test, Shore scleroscope.

Toughness
Toughness is the property of a material to resist fracture due to high impact. It is measured by the amount of energy that a unit volume of the material has absorbed after being stressed up to the point of fracture.
This property is desirable in parts subjected to shock and impact loads. Normally the toughness of the material decreases when it is subjected heat.

Ductility
Ductility is the property of a material enabling it to be drawn into a wire with the application of a tensile force. A ductile material must be both strong and plastic. The ductility is usually measured by the terms, percentage elongation and percentage reduction in area. The ductile material commonly used in engineering practice are mild steel, copper, aluminum, nickel, zinc, tin and lead.

Brittleness
It is the property of breaking of a material with little permanent distortion. Brittleness of a material is opposite to ductility property.
Brittle materials are withstanding compression load. When subjected to tensile loads snap off without giving any sensible elongation. Cast iron is a brittle material.