# Pune University Exam Paper

## RELIABILITY(Elective-II)(Sem.- II)

Instructions to the candidates:

1)                  Answer any three questions from each Section.

2)                  Answers to the two sections should be written in separate books.

3)                  Neat diagrams must be drawn wherever necessary.

R)    figures to the right indicate full marks.

5)                  Use of logarithmic tables slide rule mollier charts, electronic pocket calculator and steam tables is allowed.

6)                  Assume suitable data, if necessary.

SECTION -1

QI) a) A series of tests are conducted on 850 components and the total duration

of tests is 12 Hrs. The no. of components failed during each hourly interval is noted and given in table. Pind :      [10]

i) pailure density

ii)                                 Hazard rate

iii)                            Reliability

 Time(t) Hr. 1 2 3 4 5 6 7 8 9 10 11 12 No. of failures 120 85 71 62 53 50 52 42 38 40 45 102

b) Explain Availability & Maintainability. Also state the types of availability.[6]

Q2) a) In an engineering manufacturing plant 70% of crankshafts are ground by machinist R & 30% by machinist S. Prom past experience it has been observed that crankshafts ground by machinist R & S contains 6% and 4% defective. Pind the probability that it was ground by the machinist R.[10]

b) Explain center limit theorem.                      [6]

P.T.O.

 Q3) a) Calculate the reliability of the system shown in Pig I. The values in the Block show reliability of individual components in the system. [10]

b) Eight components are connected in parallel to achieve the system reliability of 0.94. Determine the reliability of each component. How many additional number of components to be added in parallel to increase the reliability upto 0.96.             [6]

Q4) a) Calculate the system reliability for the following fig.2     [10]

b)               In a life test of 20 samples, following data is collected for the failure of component in hours. Determine the mean time to failure and reliability at 1300 Hrs.

840, 861, 905, 960, 975, 1020, 1060, 1120, 1150, 1200, 1215, 1235, 1260, 1280, 1300, 1315, 1340, 1365, 1375, 1400.    [6]

Q5) Write short note on following (any three).            [18]

a)                 Baye’s theorem and its applications.

b)                Probability Distributions.

c)                 AGREE Method of Reliability Allocation.

d)                Total probability theorem .

e)                 Types of redundancies.

SECTION – II

Q6) a) The mean strength and the standard deviation of a bolted joint are 3000 kg/cm2 and 260 kg/cm2 respectively. The joint is loaded such that stress induced has a mean value of 2500 kg/cm2 with a standard deviation of 40 kg/cm2. Assuming that shear strength and the induced stresses are independent and normally distributed, find out the probability of survival of the bolted joint. Extract of data from statistical table is given below.

 z 1.2 1.3 1.4 1.5 1.6 1.7 1.8 0 (Z) 0.8849 0.9032 0.9192 0.933 0.945 0.955 0.963

[8]

b) Explain different types of loads considered in designing different machines.                                          [8]

Q7) a) The following data refer to predicted reliability of six components in series. In case the desired reliability of the system is not to fall below

 component 1 2 3 4 5 6 Predicted reliability 0.99 0.9 0.995 0.95 0.95 0.98

[8]

b) Explain the magnified loading and sudden death testing for a system.[8]

Q8)    a)   A logic gate diagram for PTA study has been shown in Pig.1. The failure

 b) Explain the systematic procedure to be followed for Pailure modes, Effects and criticality analysis.                                                                                                [8]

probabilities of ‘a’, ‘b’, V, ‘d’, and V are 0.01, 0.003, 0.005, 0.007 and 0.09 resp. Pind the system reliability.  [8]

Q9) a) In a short sample Accelerated life Testing of a system, based on weibull

distribution the following data is recorded.

 Pailure No. 1 2 3 4 5 6 7 8 9 MTTP (Hrs.) 24 22 12 28 35 38 30 19 25

[8]

b)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                Explain the various accelerated life test carried out for reliability analysis. [8] QIO) Write short note on following (any three).                [18]

 a) Bath Tab Curve. b) Reliability Testing. c) Pault Tree Analysis. d) Quality and Safety. e) Tie set and Cut set.