Mechanical properties of a materials

Mechanical properties of a materials

    ➤ Elasticity:  

    → Elasticity of a material is its power of coming back to its original position after deformation when the stress or load is removed. 

    → Elasticity is a tensile property of its material.

    ➤ Stiffness:  

    → It is the property of a material due to which it is capable of resisting deflection or elastic deformation under applied loads. also called rigidity. 

    → The degree of stiffness of a material is indicated by the young’s modulus. 

    → The steel beam is stiffer or more rigid than aluminum beam.

    ➤ Plasticity:  

    → The plasticity of a material is its ability to change some degree of permanent deformation without failure. 

    → This property is widely used in several mechanical processes like forming, shaping, extruding, rolling etc. 

    → Due to this 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. 

    → Plasticity increase with increase in temp.

    ➤ Malleability:  

    → Malleability of a material is its ability to be flattened into their sheets without creaking by hot or cold working. 

    → Aluminum, copper, tin lead steel etc. are malleable metals.

 

    ➤ Ductility:  

    → Ductility is that property of a material, which enables it to draw out into thin wire. 

    → Mild steel is a ductile material. 

    → The percent elongation and the reduction in area in tension is often used as empirical measures of ductility.

    ➤ Brittleness:  

    → The brittleness of a material is the property of breaking without much permanent distortion. 

    → There are many materials, which break or fail before much deformation take place. Such materials are brittle e.g. glass, cast iron. 

    → Therefore a non-ductile material is said to be a brittle material. 

    → Usually the tensile strength of brittle materials is only a fraction of their compressive strength. 

    → A brittle material should not be considered as lacking in strength. It only shows the lack of plasticity.

    ➤ Toughness:  

    → Toughness is a measure of the amount of energy a material can absorb before actual fracture or failure takes place. 

    → The toughness of a material is its ability to withstand both plastic and elastic deformation. 

    → The work or energy a material absorbs is called modulus of toughness.

    → For Examples: If a load is suddenly applied to a piece of mild steel and then to a piece of glass the mild steel will absorb much more energy before failure occurs. 

    → Thus mild steel is said to be much tougher than a glass. 

    ➤ Hardness:  

    → Hardness is defined in terms of the ability of a material to resist screeching, abrasion, cutting, indentation or penetration. 

    → Many methods are now in use for determining the hardness of a material. They are Brinell, Rockwell and Vickers.

    → Hardness of a metal does not directly related to the hardenability of the metal. 

    → Hardenability is indicative of the degree of hardness that the metal can acquire through the hardening process. i.e., heating or quenching.

    ➤ Impact Strength:  

    → It can be defined as the resistance of the material to fracture under impact loading, i.e under quickly applied dynamic loads.

    → Two standard tests are normally used to determine this property.

    ➤ Fatigue :  

    → Failure of a material under repeated stress is known as fatigue and the maximum stress that a metal can withstand without failure for a specific large number of cycle of stress is called Fatigue limit.

    ➤ Creep:  

    → The slow and progressive deformation of a material with time at constant stress is called creep. 

    → There are three stages of creep. 

    → In the first one, the material elongates rapidly but at a decreasing rate. 

    → In the second stage, the rate of elongation is constant. 

    → In the third stage, the rate of elongation increases rapidly until the material fails. 

    → The stress for a specified rate of strain at a constant temperature is called creep strength.