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GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA ENGINEERING – SEMESTER – V-EXAMINATION – WINTER 2015
Subject Code: 3351902 Date: 10/12/2015
Subject Name: Design of Machine Elements
Time: 10:30 AM TO 1:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make Suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of programmable & Communication aids are strictly prohibited.
5. Use of only simple calculator is permitted in Mathematics.
6. English version is authentic.
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Q.1 Answer any seven out of ten. 14
1. List types of stresses.
2. Define F.O.S.
3. List most materials used in manufacturing of machines.
4. What is standardization ?
5. List main factors influencing design of machine elements
6. List types of loads.
7. What is stress concentration ?
8. What are preferred numbers ?
9. List and shortly explain two main properties of material which are useful in design.
10. List types of keys and their uses.
Q.2 (a) List type of riveted joints. Discuss (equations for) strength and efficiency of riveted joint. 03
OR
(a) Find force and consequently tensile stress induced in M24 size bolt due to initial tightening 03
(b) List types of welded joints., with their symbols. 03
OR
(b) List advantages and disadvantages of screwed joint. 03
(c) A double riveted lap joint is made between 15 mm thick plates. Ihe rivet diameter and pitch are 25 mm and 75 mm respectively. If ultimate stresses are 400 MPa in tension, 320 MPa in shear and 640 MPa in crushing, find minimum force which will rupture the joint. 04
OR
(c) A plate 100 mm wide and 10 mm thick is to be welded to another plate by means of double parallel fillets. Plates are subjected to a static load of 80 kN. Find the length of weld if permissible shear stress in the weld does not exceed 55 MPa. 04
(d) A cotter joint takes a pull of 30 kN. Find rod diameter 'd', spigot diameter 'd1' , and cotter thickness 't' of the joint if permissible stresses for the joint material (all parts are of same material) are 55 MPa, 100 Mpa and 40 MPa for tensile, crushing and shear respectively. 04
OR
(d) A knuckle joint takes a pull of 70 kN. Find rod diameter 'd', knuckle pin diameter 'dp' , and eye end thickness 't' of the joint if permissible stresses for the joint material (all parts are of same material) are 70 MPa, 110 Mpa and 66 MPa for tensile, crushing and shear respectively. Use empirical relation for dp, and t . Check for induced shear stress in knuckle pin. 04
Q.3 (a) List types of levers. Draw neat sketches of three main c/s sections used as lever sections 03
OR
(a) Why brass / bronze material is used in hole of lever at fulcrum pin ? 03
(b) Write equations of modulus of section for rectangular section and elliptical section 03
OR
(b) Draw neat sketch of bell crank lever , label it's elements' name. 03
(c) Draw neat sketch of semi-elliptical leaf spring and label it's parts. Explain it's construction( with material of it's parts) and working. 04
OR
(c) A vertically downward load of W= 4.5 kN is acted on horizontal arm which is 500 mm long, of a bell crank lever. On short arm which is 150 mm long and perpendicular to horizontal arm has a effort 'p' acting at right angle to it's own axis. Find rectangular c/s of lever if width 'b' of section is 3 times the thickness 't' and allowable bending stress for forged lever material is not to exceed 75 MPa. 04
(d) Draw appropriate neat sketch of eccentric loading and explain eccentric loading (with their equation) of such m/c elements. List machine elements subjected to eccentric loading 04
OR
(d) A “ L” bracket carries a load of 42 kN with rectangular cross section. Eccentricity of load with centre of bigger side of c/s section is 75 mm. Take safe tensile stress of 60 N/mm2. Find c/s section of bracket if h= 2b for bracket section. 04
Q.4 (a) List types of shafts. Normally which material is used as a shaft material ? 03
OR
(a) Draw neat sketch of muff coupling and write empirical relational equations for it's design 03
(b) A helical compression spring is to take load of 1000 N .The maximum compression on the spring is 80 mm. The spring index is 4.84.Take mod. of rigidity G = 85 kN/mm2. Find mean diameter 'D', wire diameter 'd'.Approximate no. of turns 'n'= 30. 04
OR
(b) A solid shaft is transmitting 1 MW power at 240 R.P.M. Determine diameter of shaft if maximum torque transmitted exceeds mean torque by 20%. Assume maximum allowable shear stress as 60 MPa. 04
(c) A C.I. flange coupling is required to transmit 15 kW at 900 R.P.M. Find shaft diameter 'd', hub diameter 'D', no. of bolts 'n' and bolt diameter 'db'. Permissible stresses - shear [τ] for shaft and bolt material = 40 Mpa and crushing stress for bolt material = 80 Mpa and shear stress for C.I. flange material [τ] = 8 MPa. 07
Q.5 (a) A thin cyl. pressure vessel of 500 mm internal diameter and 20 mm thickness is subjected to an internal pressure of 2 N/mm2. Find hoop stress, longitudinal stress and max. Shear stress. 04
(b) Find 14 steps of various speeds (range) between 25 R.P.M. to 2000 R.P.M. using preferred numbers theory. 04
(c) Broadly classify anti-friction bearing. Write their advantages and applications. 03
(d) Define and classify pressure vessels. Write condition for thin and thick pressure vessel. Write name and equations for two types of stresses developed in thin cyl. shell subjected to internal pressure.03
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