TECH SPOT: SAMPLE CRE QUESTIONS (Part 25)

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1. Which of the following is NOT true about the Taguchi DOE approach?
I. It includes the concept of loss function in factorial experiments.
II. It assumes losses occur when a process fails to meet a target value.
III. It assumes losses are due to variability within the process.
IV. It assumes that the loss function is a step function relative to the specification limits.
A. I only

B. II only

C. III only

D. IV only

 

2. In general, reliability testing is performed for which of the following reasons?
I. To detect unanticipated failure modes.
II. To compare estimated failure rates to actual failure rates.
III. To monitor reliability growth over time.
IV. To meet or exceed customer expectations.

A. I and III only

B. II and IV only

C. I, II and III only

D. I, II, III and IV

 

3. The time to failure of a component is Weibull distributed, β=0.5, η=10,000 hours.
What is the probability that the component will still be operational after one year?
A. 0.3922

B. 0.3214

C. 0.3680

D. 0.6320

 

4. Seventy-two bearings are available for life testing. To save test time
they are divided into six groups of twelve bearings and tested using the
sudden-death technique. The Resultant Data is :

Group 1: Bearing #3 fails at

110 hrs

Group 2: Bearing #4 fails at

75 hrs

Group 3: Bearing #11 fails at

165 hrs

Group 4: Bearing #5 fails at

310 hrs

Group 5: Bearing #7 fails at

210 hrs

Group 6: Bearing #12 fails at

270 hrs

What is the 0.90 Reliability of the bearing population?
A. 69 hrs

B. 79 hrs

C. 241 hrs

D. 120 hrs

Time1(hrs)

Number

Censor(F=1,C=0)

110

1

1

75

1

1

165

1

1

310

1

1

210

1

1

270

1

1

110

11

0

75

11

0

165

11

0

310

11

0

210

11

0

270

11

0

 

5. The ratio of the Bill of Material (BoM) turbopump field failures to the BoM turbopump bench lab test failures is:

Both Field & lab data had a Weibull β=2.59
The turbopump was redesigned to fix the problem and two units were tested in the lab for 500 hours without failure under the same accelerated conditions. What service experience should be expected in terms of characteristic life?
Hint: Use the equation for MLE η
A. 252 hrs

B. 707 hrs

C. 1000 hrs

D. 653 hrs

 

6. A first prototype for a novel laser-powered sausage slicer is built. Failures occur at the following numbers of minutes: 1.1, 3.9, 6.2, 17.8, 79.7, 113.1, 206.4 and 239.1. After each failure, the design is refined to avert further failures from the same mechanism. Determine the reliability grown coefficient β for the slicer.
A. 0.34
B. .93
C. 1.31
D. 1.15
 


 
7. Brand X aircraft manufacturing company has a backup control system that operates independently of the primary control. Each of the systems has a probability of 0.01 of failing on a particular mission.
What is the probability of at least one system functioning properly?
A. 0.9999
B. 0.9801
C. 0.9808
D. 0.99999
P(at least one system functions properly)= 1-P(none working) =1-(0.01)2=0.9999

 

8. While the AMSAA-Duane model is N(t)=λtβ ; the model can be rearranged in a number of ways to satisfy a customer’s demands for reporting. Which of the following functions could be used for plotting cumulative Failure rate and Cumulative MTBF:

A. I. & II

B. I. & III.

C. II. & IV.

D. II. & III.

 

9. In constructing programs for environmental stress screening(ESS), the selection of the stress levels and the choice of exposure times is a challenging task. Which of the following are true:
I. ESS is not a test. ESS is a screening process
II. ESS is not Burn-in, ESS stresses a product to operational extremes
III. ESS is used in manufacturing/production to catch latent failures.
IV. All items in a product line should be exposed to ESS.
A. I., II., IV.

B.I.,III., IV.

C. II., III., IV.

D. I.,II.,III.,& IV.

 

10. A test was done on ultrasonic inspection kits to determine how effective they are in discovering microscopic cracks in aircraft parts. When a crack was present, the equipment signaled a crack 98% of the time. There was a “false alarm” on 3% of the parts which had no cracks. Suppose five percent of all the parts have a crack in them. If the percentages in the test can be assumed to be the true probabilities, find the probability that a part is really bad when a kit signals a crack.
A. 0.9215

B.0.9225.

C. 0.6322.

D. 0.7533.

 

 

EXTRA Problem:
An engineer just ran 50 compressor start tests with NO failures.
The engineer needs to pass the customer’s requirement of 80% confidence of at least 0.90 Reliability.
Has the engineer achieved that goal?
A. Yes
B. No
C. More data required
D. Question not worded correctly
 
Confidence Interval Estimate of Reliability

We want 80% of the intervals we would estimate from repeated
Testing to contain the true value.
Therefore,

1 – Confidence =

Therefore, 0.2=

So, R = 0.968

For N=50, no failures, we can state with 80% confidence that
the true unknown reliability lies between 0.968 and 1.0.
The answer is A.

 

 

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TECH SPOT: SAMPLE CRE QUESTIONS (Part 25)

1. Which of the following is NOT true about the Taguchi DOE approach?I. It includes the concept of loss function in factorial experiments.II. It assumes losses occur when a process fails to meet a target value.III. It assumes losses are due to variability within the process.IV. It assumes that the loss function is a step

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TECH SPOT: SAMPLE CRE QUESTIONS (Part 24)

1. A computer chip manufacturer averages 7 defects per chip. What is the probability of a chip containing less than 3 defects?A. 0.00638 B. 0.02234 C. 0.02963 D. 0.02872     2. Given the following data: (where (-) indicates censored) -309,229,386,-104,180,-217,-167,168,122,138Determine the best fit Weibull parameters β,η, t0? A. β=2.76,η=261.1, t0= 0.0 B. β=0.88,η=147.86, t0=113.76

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