Page 53 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

• Resilience: Ability of material to absorb energy up to elastic limit

• Desirable property for spring materials
• Indicated by area under stress strain curve up to elastic limit
• Brittleness: Fracture without much deformation
• Opposite to ductility
• Ex for brittle material: Glass, Cast iron

• Ductility: Undergo deformation under tensile load without rupture.
• This property enables wire drawing.
Malleability: Undergo deformation under compressive load without rupture
• This property is useful in rolling of thin sheets
• Elasticity: Ability of a material to regain its original shape and size after removal of load

Ex: Steel, rubber
• Plasticity: Ability of material to be permanently deformed (without fracture) even after the load is removed.
• This property finds its use in forming, shaping and extruding operations of metals.
Creep: Slow and continuous deformation of material with time under constant load
• Metals shows creep at high temperature where as plastic creep at low temperature
• Ex: Beams in the roof of building shows creep with time.
• This property is considered in designing of boilers, IC engines, steam turbines etc.
• Fatigue: Failure of material caused due to cyclic or fluctuating loads.
• Occurs abruptly without showing any sign of failure
• This property is considered in designing of motor shafts, wire ropes, springs etc. subjected to cyclic loading.
Stiffness: Resistance of material to elastic deformation
• Modulus of rigidity is the measure of stiffness
• Materials which suffer less deformation under load have high degree of stiffness.
• This property is made used in spring balance and spring controlled measuring instruments.
Chemical Properties

• Corrosion resistance: Resistance to deterioration or decaying of metal by chemical or electrochemical
reaction with its environment.
• Corrosion degrade material properties and reduce economic value.
• Acidity: Substance that gives hydrogen (H+) icons or hydronium ions (H3O+) in aqueous solution.
HCI + H2O = H3O+ + CI-
• Alkalinity: Substance that gives hydroxyl icons (OH-) icons in aqueous solution
Na (OH) + H2 O = Na+ + OH-

Chemical properties
• Corrosion resistance: Resistance to deterioration or decaying of metal by chemical or electrochemical
reaction with its environment

• Corrosion degrade material properties and reduce economic value
• Acidity: Substance that gives hydrogen (H ) ions or hydronium ions(H O ) in aqueous solution
+
+
3
HCI + H O = H O + Cl -
+
2 3
• Alkalinity : Substance that gives hydroxyl ions (OH ) ions in aqueous solution
-
Na(OH) + H O = Na + OH -
+
2
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CITS : WCS - Mechanical - Exercise 2