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Factors to be considered for selection of material for design of machine elements a) Availability: Material should be available easily in the market. b) Cost: the material should be available at cheaper rate. c) Manufacturing Consideration: the manufacturing play a vital role in selection of material and the material should suitable for required manufacturing process. d) Physical properties: like colour, density etc. f) Mechanical properties: such as strength, ductility, Malleability etc. g) Corrosion resistance: it should be corrosion resistant.

A) X10Cr 18 Ni9 Mo 4 Si 2 : High Alloy steel having carbon 0.10% , chromium 18%, nickel 9 % ,Molybdenum 4% & silicon 2% B) XT72W18Cr4V1: high speed tool steel having carbon 0.72% ,chromium 4% , tungsten 18% , vanadium 1% 

Stress concentration: Whenever a machine component changes the shape of its cross section, the simple stress distribution no longer holds good and the neighbourhood of the discontinuity is different. This irregularity in the stress distribution caused by abrupt changes of form is called ‘stress concentration’.

The different areas covered under the ergonomics are: 1. Communication between the man (user) and the machine. 2. Working environment. 3. Human anatomy and posture while using the machine. 4. Energy expenditure in hand and foot operations. Communication between man and machine  The machine has a display unit and a control unit.  A man (user) receives the information from the machine display through the sense organs.  He (or she) then takes the corrective action on the machine controls using the hands or feet.

Theories of Failures

Maximum shear stress theory is explained below

The principal theories of failure for a member are as follows:

(i) Maximum principal or normal stress theory

(ii) Maximum shear stress theory

(iii) Maximum principal or normal strain theory

(iv) Maximum strain energy theory

(v) Maximum distortion energy theory

Maximum normal stress theory (Maximum principal stress theory or Rankines theory

Ergonomics is defined as the scientific study of the man – machine working environment relationship and the application of anatomical, physiological, psychological principles to solve the problems arising from this relationship.

When a machine part is subjected to a constant stress at high temperature for a long period of time, it will undergo a slow and permanent deformation called ‘creep’. This property is considered in designing internal combustion engines, boilers and turbines

(i) Dead or steady load (ii) Live or variable load (iii) Suddenly applied or shock load (iv) Impact load