Lecture 1.pptx...............................

besttttttttttttttttttt

1. PROPERTIES OF MATERIALS Different materials possess different properties in varying degree and therefore behave in different way under given conditions These properties include Mechanical Electrical Thermal Chemical Magnetic Physical A design engineer is interested in the behavior of materials under load which is mechanical in nature, for the design of machines & structures . Any material subjected to a load either deforms , yield , or break , depending upon the magnitude of the load . We are basically interested in knowing as to how a particular material will behave under applied load i.e . In knowing the mechanical properties.

2. WHY TO STUDY TO MECHANICAL PROPERTIES OF MATERIALS? An elementary knowledge of the properties of the various materials enables the designer to decide which particular material is the best to use for any particular purpose . An elementary knowledge of the principal processes by which iron and steel are produced is also essential to every engineer, As in specifications of engineering designs and structures it is frequently stated by which particular process the material to be employed is to be made . Certain terms relating to the properties of materials are constantly being used by engineers . The exact meaning of these terms must therefore be explained at this stage.

3. 1. Tenacity / Strength It is the resistance offered by a material when subjected to external loading . So, stronger the material the greater the load it can withstand . Depending upon the type of load applied the strength can be Tensile Compressive Shear Torsion 2. Hardness It is the ability of a material to resist scratching , abrasion , indentation . Thus machine cutting tools are made hard To prevent them from being blunted By contact with the materials they are intended to cut. Softness is the converse of Hardness.

4. 3. Brittleness The property of material to br eak readily without much permanent distortion, subjected to shocks. Usually, the tensile strength of brittle materials I s only a fraction of their compressive strength . Therefore, a non-ductile material is said to be a brittle material. Brittle Material Should not be considered as lacking strength . It only shows the lack of plasticity . Do not have Yield Point on Stress-Strain Diagram + Low Value of E Glass Cast Iron Examples 4. Ductility The property possessed by certain bodies that they may be drawn out in the direction of their length . The elongations are permanent . It enables the material to draw out into thin wire on application of the load . Possess the properties both of tenacity and softness . The ductility decreases with increase of temperature . Mild steel, gold , silver, copper , aluminum, etc. Examples

5. 5. Malleability Malleability of a material is its ability to be flattened into thin sheets without cracking by hot or cold working. A body is said to be malleable when it can be beaten out and extended in all directions. Ductility is a tensile property, whereas malleability is a compressive property Malleability increases with increase of temperature. Aluminum, copper, tin, lead, steel, etc. are malleable metals. 6. Welding Power Separate pieces of certain metals, when heated to a high temperature, may be joined together by hammering so as to form one piece. Such metals are said to be weld able. 7. 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. The greatest stress that a material can some endure without taking up called permanent elastic limit. set is

6. 8. Stiffness (Rigidity) The resistance of a material to deflection is called stiffness or rigidity. Stiffness is measured by young’s modulus E. The higher the value of the young’s modulus, the stiffer the material. 9. Plasticity The plasticity of a material is its ability to undergo some degree of permanent deformation without failure. Due to this properties various metal can be transformed into different products of required shape and size. Plasticity is an important property and widely used in several mechanical processes like forming, shaping, extruding and many other hot and cold working processes. In general, plasticity increases with increasing temperature This conversion into desired shape and size is effected either by the application of pressure, heat or both.

7. 10. Toughness 11. Hardenability The toughness of a material is its ability to withstand both plastic and elastic deformations. Toughness is a measure of the amount of energy a material can absorb before actual fracture or failure takes place. “The work or energy a material absorbs is called modulus of toughness”. For e.g., 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. wrought iron, mild steels It is a highly desirable quality for structural and machine parts to withstand vibration. shock and Hardenability is the degree of hardness that can be imparted to metal by process of hardening. The material is heated above a certain temperature and then suddenly quenched in a cold oil or water bath. Hardness does not directly relate to the hardenability. Hardenability is indicative of the degree of hardness that the metal can acquire through the hardening process. i.e., Heating or quenching.

8. 12. Impact Strength 13. Resilience 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. The IZOD impact test. The CHARPY test. Resilience is the capacity of material to absorb energy elastically. On removal of the load, the energy stored is released as in a spring. The quantity gives capacity of the material to shocks and vibrations. bear The maximum energy which can be stored in a body up to elastic limit is called resilience. the proof