Reliability engineering.
 
1. Which statement is untrue?
Reliability R(t) is defined as the probability that a system will perform satisfactorily under specific conditions within a certain time interval.
Reliability is the complement of the probability of failure R(t)=1-F(t)
For rolling bearings the L10 life is often used, which corresponds to a probability of survival of R(t)=0.9 and a probability of failure of F(t)=0.1
A deterministic approach in calculating the torque a press fit can transfer is generally satisfactorily.

2. An LRC circuit consists of an inductor R=0.95, resistor R=0.85, capacitor R=0.9, and AC voltage source R=0.92 all connected in series.
The overall reliability of the circuit will be R=0.22
The overall failure probability of the circuit will be F=0.22
The overall reliability of the circuit will be R=0.67
The overall failure probability of the circuit will be F=0.67

3. A computer has three cooling fans connected in parallel. One fan will provide enough cooling and the reliability of the individual fans R=0.9.
The system reliability of the fans connected in parallel increases to R=0.95
The system reliability of the fans connected in parallel increases to R=0.975
The system reliability of the fans connected in parallel increases to R=0.99
The system reliability of the fans connected in parallel increases to R=0.999

4. A cooling system of a computer consists of three cooling fans connected in parallel to one main power supply. One fan will provide enough cooling. The reliability of the individual fans R=0.9, of the power supply R=0.95.
The reliability of the cooling system will be R=0.9
The reliability of the cooling system will be R=0.95
The reliability of the cooling system will be R=0.99
The reliability of the cooling system will be R=0.999

5. Which statement is untrue?
Fault tree analysis (FTA) is a procedure to help establish system reliability.
Fault tree analysis (FTA) is a procedure to help identify critical components.
Fault tree analysis (FTA) is a procedure to help identify failure modes of components.
The fault tree itself is a graphical representation of events that lead to a specific failure (top event).

6. Which statement is untrue?
Failure mode and effect analysis (FMEA) is a procedure to help identify possible failure modes of components and their impact on the functioning of the system.
FMEA is a key tool in quality improvement.
FMEA is without statistics, however, provides very limited insight into the system reliability.
FMEA is generally initiated after a failure has occurred.

7. Which statement is untrue?
Failure analysis (FA) refers to the understanding and categorizing of a failure mode, not necessarily to find the rout cause.
Root cause failure analysis (RCFA) includes the investigation towards root causes of failures.
Root cause analysis (RCA) is a procedure to identify the root causes for a failure and the actions to necessary to prevent recurrence in future.
RCA is generally initiated in design stage as part of a reliability improvement program.

8. Which statement is untrue?
The "Relative frequency diagram" represents the number of failures within time intervals, i.e. the failure distribution over time.
The "Probability density function" of failure represents the number of failures within time intervals divided by the total number of failures, i.e. the probability of failure density over time.
The "Normal distribution" also called the "Gaussian distribution" is the most widely used probability density distribution.
Other probability density distributions are the "Wear out", "Bathtub", "Random" and "Infant mortality" functions.

9.
A quantity of 100 components all fail within one year of service. 5 components failed during the first month, 15 components have failed within 2 months. Which statement is untrue?
The probability of failure that one component fails within two months F(2)=0.15
The probability of failure that 15 components fail within two months F(2)=0.15
The reliability of the individual components for two months service R(2)=0.85
The cumulative failure also called the failure density in the first month is f(2)=0.05

10.
The diameter of a batch of shafts is normally distributed. It is assumed that 99.7% of the shafts have a diameter within 100.1mm.  Which statement is untrue?
The mean value of the diameter of all shafts will be 10 mm.
99% of the shafts will have a diameter within 100.086mm
95% of the shafts will have a diameter within 100.065mm
1.25% of the shafts will have a diameter smaller than 9.935mm