28-07-2012, 04:49 PM
A Presentation on Design of Machine Elements
A Presentation.ppt (Size: 3.14 MB / Downloads: 133)
Classification of Engineering Materials
Metals and their alloys
1. Ferrous metals 2. Non-ferrous metals
cast iron, steel, copper, brass,Zinc
Non metals such as glass,rubber,Plastic
Availability of materials
Suitability of materials for working conditions in services
Cost of the materials
Mechanical Properties of Metals
Strength – ability of a material to resist the externally applied forces without breaking
Stiffness- ability of a material to resist deformation under stress
Elasticity – regain its original shape after deformation when external forces are removed
Ductility – property of a material enabling it to draw into wire when tensile force is applied
Brittleness – property of the material opposite to ductility
Toughness- property of the material to resist fracture due to high impact loads
Resilience – property of the material to absorb energy and to resist shock and impact loads
Creep – when subjected to constant stress at high temperature for a long period it will undergo a slow and permanent deformation
Malleability – special case of ductility which permits materials to be rolled or hammered into thin sheets
Hardness – important property of the metals – it embraces many different properties such as resistances to wear, scratching, deformation, and machinability etc.,
Standardization
Minimize variety
Standard components and parts can be obtained readily and economically from the market
Makes the repair and maintenance of machine simple
Reduce the time and effort to design and manufacture new machines
Mass production also becomes possible due to standardization
Preferred Numbers
Preferred numbers are nothing bet a series of numbers in a geometric progression
Used for standardization
Reduce unnecessary variations in sizes of an articles
Used for fixing the speed, power capacities, structures
By experience that discrete increment of particular measure, if maintained in GP gives a logical, uniform and proportionate characteristic variation pattern.