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Answers to CRE questions in December 2018 Newsletter

The mean number of life units during which all parts of the item perform within their specified limits, during a particular measurement interval under stated conditions’. This is the definition of ___________ for a repairable item.
o MTBF ‐ Mean Time Between Failures                             
o MTBM ‐ Mean Time Between Maintenance
o MTTF ‐ Mean Time To Failure                                          
o MDT ‐ Mean Maintenance Downtime

The sum of corrective maintenance times at any specific level of repair, divided by the total number of failures within an item repaired at that level, during a particular interval under stated conditions? This is the definition of __________.
o MTBM ‐ Mean Time Between Maintenance                 
o MTBF ‐ Mean Time Between Failures
o MTTR ‐ Mean Time To Repair                                           
o MDT ‐ Mean Maintenance Downtime

When a test is terminated before all units fail the resulting data are known as:
o right censored                                                                     
o interval data
o left censored                                                                       
o None of these

The main responsibilities of a Failure Review Board include all except which of the following?
o Assessing failures                                                                                        
o Setting up accelerated life tests
o Monitoring Corrective Action to prevent failure Reoccurrence           
o Monitoring reliability growth.

Which one is the most important input for Reliability Program development?
o MTBF prediction data                                  
o Customer requirements from their mathematical modeling  data
o Accelerated life test data                            
o Customer requirements from their empirical data

Customer inputs at the concept stage of design are used to drive all except which of the following?
o Initial reliability predictions based on field data              
o Development of operational profiles
o Criteria for acceptable product performance                   
o Identification of suitable design verification tests

In which of the following life cycle phases is Reliability prediction most useful as an aid during tradeoffs between various operating scenarios (such as operating conditions, customer usage)?
o Concept                                  
o Production
o Development                         
o Test

Manufacturing errors are the primary reason for products failing during the:
o infant mortality stage.                                     
o wear‐out stage.
o useful life stage.                                               
o infant mortality and wear‐out stages

During its useful life period, the MTTF for a particular type of light bulb is 2000 hours. Out of 1000 of these bulbs, how many will have burned out after 1500 hours?
o 472                                          
o 736
o 528                                          
o 750

A unit has a design life of 1,000 days. It has a MTBF that is estimated to be 50 days, requiring a mean time to repair of 15 days. The acquisition cost for this unit is $150,000. Each time that the unit fails, a fixed cost of $3,000 is incurred  along with a variable cost of $500/day. What is the expected cost of this unit over its design life?
o $240,000                               
o $360,000
o $150,000                             
o $210,000

Picture © B. Poncelet

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