# Design of Machine Elements-1 July 2009

Fifth Semester B.E. Degree Examination, June-July 2009  Design of Machine Elements – I

Note: 1 Answer any FIVE full questions, selecting at least TWO questions from each part.

2. Use of design data hand book is permitted.

3.Missing data should be suitably assumed and clearly stated.

PART-A

1.a. Write brief note on general procedure used in design.

b. Explain the following theories of failure:

(i) Maximum normal stress theory.

(ii) Distortion energy theory.

c.   A steel rod 1.5 meter long resists an impact load of 2 kN dropped 50mm along its axis. Limiting the maximum stress in the rod to 15 diameter of rod required ii) Impact factor. Use E = 200 GPa.

2. a. Explain the following:

(i) Notch sensitivity ii) Stress concentration factor.

b.  A bolt in an assembly is subjected to a pull of 1000N along its axis and a shear force of 500N, what will be the maximum stress induced in the bolt. If the bolt is made of SAE 1045 annealed steel, is the bolt is safe given that the diameter of bolt is 12mm.      (07 Marks)

c.   A 50mm diameter steel rod supports a 9000N load and in addition is subjected to torsional moment of 100 N-m. Determine the maximum normal and the maximum shear stresses.

3. a. Explain endurance limit and endurance Strength with the help of S.N. diagram

b. A hot rolled steel rod is subject to a torsional load that varies from  +440 N-m  clockwise to 110 N-m counter clockwise and an applied bending moment bending  varies from -220 N-m. The rod is of uniform cross Section. Determine the required rod diameter. The material has an ultimate tensile strength of 550 MPa and a yield strength of 410 MPa  Design based on a factor of safety of 1.5. Take the endurance limit as half the ultimate.

4. A Machine component is subjected to a bending load which is completely cyclic as shown Fig in 4(a) Determine in the suitable value of load W. If the maximum stress induced is not to exceed 100 N/mm2 and  200 N/mm2 Ocnd = 200 N/mm

(b)  A bracket is fixed to the wall by means of four bolts and loaded as shown in Fig.4(b). Calculate the size of the bolts if the load is 25 kN and the yield stress is 380 N/mm . The factor of safety is taken as 2.5. Use maximum shear stress theory.

PART-B

5 . A shaft supported between bearing 400mm apart gets its drive through a gear drive.. A gear is mounted 200mm to the right of the left hand bearing and is driven by a pinion just above it. The gear has a module of 10mm, number if teeth is equal to 40 and pressure angle (j>=20°, the power received is 20kW at 500 rpm. Overhanging to the right hand bearing by 200mm there is a pulley of diameter 200mm, the belt drive is inclined at an angle of 30° with the vertical and is away from the shaft. The ratio of belt tension is taken as 3:1. Design a shaft assuming that the allowable stress as 100 N/mm2 in tension and 40 N/mm2 in shear, for suddenly applied loads with minor shocks.

6.(A) 45mm diameter, shaft is made of steel with a yield strength of 40 MPa. A parallel key of size 14mm wide and 9mm thick, made of steel with a yield strength of 340 MPa. Find the required length of key, if the shaft in loaded to transmit the maximum permissible torque. Design based on maximum shear stress theory and take factor of safety as

(b). Design a bushed-pin type flexible coupling to connect a pump shaft to a motor shaft transmitting 32 kW at 960 rpm. The overall torque is 20 percent more than mean torque. The material properties are as follows:

i)    The allowable shear and crushing stress for shaft and key material is ?0 MPa and 80 MPa respectively.

ii)    The allowable shear stress for cast iron is 15 MPa.

iii)   The allowable bearing pressure for rubber bush is 0.8

iv)   The material of the pin is same as that of shaft and key.

7.(a) A pulley has been fabricated by welding the rim of pulley to the annular web plate by a weld of size 3mmx3mm, where as hub is welded to the web plate by 5mmx5mm weld. Determine save power that can be transmitted by this pulley and welded considering only welded joint.

(b) An eccentric loaded connection is as shown in Fig.7(b). Determine the size of weld, if maximum share stress induced in weld is not exceed 75 N/mm2

8. (a) A tie bar in abridge consists of a plate 350mm wide and 20mm thick. It is connccted by a e thickness by a cover butt joint. Design an economical structural joint, if le stresses are, tensile stress 90 N/mm2, shear stress 60 N/mm2, Compressible 150 N/mrn2.

(b) A triple-threaded power screw is used in a screw jack, has a nominal diameter of 50 mm and a pitch of 8mm. The threads arc square shape and the length of the nut is 48 mm. The screw jack is used to lift a load of 7.5 kN. The coefficient of friction at the threads is 0.12 and the collar friction is negligible. Calculate

i)     The principle shear stresses in the screw rod.

ii)    The transverse shear stress in the screw and nut.

iii)   The bearing pressure for threads and

iv)   Slate whether the screw is self locking.