GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- VI (New) EXAMINATION - WINTER 2019
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Subject Code: 2162001 Date: 12/12/2019
Subject Name: Design of Mechanisms - I
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) Differentiate between crushing stress & bearing stress. 03
(b) Explain maximum principle stress theory 04
(c) Write short note on Factor of safety & preferred number 07
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Q.2 (a) Why cotter is provided with tapper ?write advantage of cotter 03 joints
(b) What is lever ?Explain principle on which it works 04
(c) Design a knuckle joint to transmit 50 kN. The design stresses may be 07 taken as 80 MPa in tension, 40 MPa in shear and 80 MPa in compression.
OR
(c) Design a Bell crank lever having load arm 500mm and effort arm of 07 150mm respectively. The maximum load to be raise is 4500N. Use the following allowable stresses for the pin and lever material. Tensile Stress =75 N/mm2 Shear Stress= 60 N/mm?2 & Bearing pressure = 10 N/mm?2
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Q.3 (a) What is limitation of Euler’s formula 03
(b) State and explain the Renkine formula in the design of column 04
(c) An offset link with an effort-of 10 mm is shown in fig.-1 The 07 thickness ‘t’ of the link is-26 mm if the permissible tensile stress for the link is 100 N/mm?,determine the load carrying capacity of the link.
OR
Q.3 (a) What is slenderness ratio 03
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(b) Why the efficiency of square thread is less than 50%. 04
(c) Explain Johnson’s formula for designing Column 07
Q.4 (a) Write down the condition for the self locking of screw. 03
(b) What is wahl’s factor? Why it is considered? 04
(c) Compare the weight, strength and rigidity of a hollow shaft of 07 same external diameter as that of solid shaft, Both the shaft are made of same material. Assume that the diameter ratio for the hollow shaft as 0.6.
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OR
Q.4 (a) Write down the condition for overhauling of screw 03
(b) Explain spring in series and spring in parallel derive formula 04 with figure.
(c) As per figure 2. A bracket is bolted to column by 6 bolts arrange 07 in two column. The distance between bolts along the row is 75mm and along the column 50mm. The joint is subjected to maximum eccentric force of S0KN acting at 150mm away from the centre of column. Taking allowable stress in the bolt as 150N/mm2, Determine the size of each boolt.
Q.5 (a) What are end fixity coefficient? 03
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(b) Explain hoop stress and Longitudinal Stress. 04
(c) Design closed coil helical spring (neglecting the effect of stress 07 concentration) from following data
Maximum load =2750N
Minimum load= 2250N
Axial deflection =6 mm
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Spring index= 5
Permissible shear stress= 420 Mpa
Modulus of rigidity= 84 kN/mm?
OR
Q.5 (a) What is mean by dynamic load & static load? 03
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(b) Write the terminology of semielliptical leaf spring With neat 04 sketch.
(c) Two helical spring are connect in series .one of spring is mad of 07 6 mm dia. wire with spring index of 5 and 12 coil . other is made of 7 mm dia. wire with spring index 6 and 18 coil . calculate the spring rate for two springs. Determine the maximum axial load that can be supported by the comination of spring .the allowable shear stress is 450 Mpa and modulus of rigidity is 80 GPa
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