## Design of Machine Elements I - Dec 2016

### Mechanical Engg (Semester 5)

TOTAL MARKS: 100

TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.

(2) Attempt any **four** from the remaining questions.

(3) Assume data wherever required.

(4) Figures to the right indicate full marks.
**1(a)** Explain the following:

Factor of safety and service factor.

Standard & codes.

Preferred series.(6 marks)
**1(b)** Two 50 mm shaft are connected by unprotected type flange coupling. The no. of bolts used are 6 on 150 mm bolt PCD. The shaft transmits 30 KW at750 rpm. For the following safe stresses

Shear stress for shaft-63 Nmm^{2}

Shear stress for flange material-10N/mm^{2}

Shear stress for key material-46N/mm^{2}

Crushing stress for key material-23N/mm^{2} Calculate: i) key Dimensions

ii) Flange Dimensions(4 marks)
**2(a)** Classify Keys. Explain why taper is provided on key.(4 marks)

### Solve any one question.Q3(a,b) &Q4(a,b)

**2(b)** A hallow circular column of external diameter 250mm and internal diameter 200 mm carries projecting bracket on which a load of 20 KN rests. The center of load from centre of column is 500 mm. Find the stresses at the sides of column and plot stress distribution plot across circular column.(6 marks)
**3(a)** Draw Neat labeled skecth of Un-Protected type flange coupling.(4 marks)
**3(b)** A forget steel bar of 50 mm diameter is sunjected to reversed bending stress of 250N/mm^{2}. Assume there is no stress concentration factor. Calculate life of bar. Use following data:

S_{ut}=600N/mm^{2}

Surface finish factor=0.43

Size factor=0.85

Reliability factor=0.897 at 90% reliability

Factor of safety=1.5(6 marks)
**4(a)** Write a short note on endurance limit modifying factors(6 marks)
**4(b)** A shaft transmit 20KW at 200 rpm. It carries a central load of 1000 N and centrally supported at 2.5 m part. The allowable shear stress for shaft is 42Mpa. The shock and fatigue factors for bending & torsion are 1.51 & respectively. Determine shaft diameter by maximum shear stress theory.(4 marks)

### Solve any one question.Q5(a,b) &Q6(a,b)

**5(a)** Explain with neat sketch, re-circulating ball screw.(4 marks)
**5(b)** A nut and screw combination having double start square threads nominal diameter 25 mm and pitch 5 mm sudjected to axial load of 1000 N. The outer and inner diameter of the screw coller is 50 and 20 mm respectively. The coefficient of friction for collar thread and screw thread are 0.15 & 0.2 respectively. The screw rotates at 12 rpm. Assume uniform wear condition, and allowable bearing pressure is 5.77N/mm^{2}. Dertermine,

i) Power required to rotate the screw

ii) Streeses in screw Body & threads

iii) No. of threads of nut in engage with screw.(12 marks)
**6(a)** Following data refers to C-Clamp

Maximum clamping force=4000N

Screw Type-Single start square threaded

Nominal Diameter=12rpm

Pitch=2mm

Coefficient of collar friction=0.25

Coefficient screw friction=0.12

Mean collar Diameter=12mm

Operator force at the end of handle=80N

Distance between the axis of handle and surface of nut in clamped condition=150 mm

Nut height=25 mm Determine,

1) Length of handle if 50 mm additional length for gripping

2) Stresses in screw body at two critical sections

3) Bearing Pressure on screw thread(13 marks)
**6(b)** Explain self locking and overhauling of power screw.(3 marks)

### Solve any one question.Q7(a,b,c) &Q8(a,b)

**7(a)** Explain with neat sketch any four types of screw fastenings.(4 marks)
**7(b)** With neat sketch write design steps for Turn Buckle, also write any two application.(6 marks)
**7(c)** A cylindrical head is connected to a flange by 12 bolts, The inside diameter of cylinder is 480 mm& maximum pressure inside is 1.5N/mm^{2} if bolt have permissible shear strength of 80N/mm^{2}. Determine the size of bolt neglecting initial tightenings.(8 marks)
**8(a)** Write advantages of welded joints. Explain primary and secondary shear stress in eccentrically loaded welded joint(6 marks)
**8(b)** A welded bracket is shown in figure 1 below, carries a load of 30 KN. Calculate size of weld if shear stress in weld is 80N/mm^{2}.

!mage(13 marks)