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2017 WINTER

Define following terms of spring:

(i) Spring rate: The spring rate is defined as the load required per unit deflection of the spring. It is also
known as spring stiffness or spring constant. Mathematically,
Spring rate, k = W / δ
Where,
W = Load
δ = Deflection of the spring
(ii) Spring index: The spring index is defined as the ratio of the mean diameter of the coil to the
diameter of the wire. Mathematically,
Spring index, C = D / d
Where,
D = Mean diameter of the coil
d = Diameter of the wire

(ii) How will select bearing from manufacturer catalogue?

The following steps must be adopted in selecting the bearing from the manufacturer’s catalogue: 1. Calculate the radial and axial load reaction (Fa and Fr) acting on the bearing. 2. Decide the diameter of the shaft on which the bearing is to be mounted. 3. Select the proper size of bearing suitable for given application, specified with speed and available space. 4. Find the basic static rating Co of the selected bearing from the catalogue. 5. Calculate the ratio (Fa / VFr) and (Fa / Co). 6. Find the value of x and y i. e. radial and thrust factor from the catalogue.

(i) State and describe in brief about four ergonomic considerations in the designing of machine elements.

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.

State the theories of elastic failure. Explain maximum normal stress theory and maximum shear stress theory with equations.

The principal theories of failure for a member are as follows:(Any four) (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  According to this theory, the elastic failure occurs when the greatest principal stress reaches the elastic limit value in a simple tension test irrespective of the value of other two principal stresses.  Taking factor of safety (F.

Explain various failures to be considered in designing a cotter joint along with the necessary sketches and strength equations.

 

It consist of 3 elements: i. Socket ii. Spigot iii. Cotter Where, d= End diameter of rod d1= Diameter of spigot/Inside diameter of socket d2= Diameter of spigot collar D1= Outer diameter of socket D2= Diameter of socket collar C=Thickness of socket collar t1= Thickness of spigot collar t= thickness of cotter b= Mean width of cotter a= Distance of end of slot to the end of spigot P= Axial tensile/compressive force σt , σc , τ= Permissible tensile,

What are the requirement of a good coupling?

A good coupling should have the following requirements: (i) It should be easy to connect and disconnect. (ii) It should transmit the full power from one shaft to another shaft without losses. (iii) It should hold the shafts in perfect alignment. (iv) It should reduce the transmission of shock loads from one shaft to another shaft. (v) It should have no projecting parts

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