Reliability_and_Maintenance_Engineering.pptx

Reliability

1. Reliability & Maintenance Engineering

2. Reliability Reliability: The reliability of the system (a component, a complex system, a computer program or a human being) is defined as the probability that the unit performs its intended function adequately for a given period of time under the stated operating condition and environment . Measures for Reliability: Probability of survival Mean time to failure Mean down time Availability Frequency of failure.

3. Metrics of Reliability: Failure rate(λ): It is the number of times the system fails in a particular interval of time. MTBF: The mean time taken before the system’s failure is known as Mean Time Before Failure (MTBF), where MTBF=1/λ Reliability of the system R(t)= e (- λt ) =e t/MTBF

4. Introduction (Cont.) Maintainability: Maintainability is the probability that a failed equipment is restored to operable condition in a specified time (down time) when the maintenance is performed under stated condition. Repair Rate (µ): It is the rate at which the system is repaired to its operating condition. MTTR: It is the average time taken by system to repair to its operating state. MTTR=1/µ

5. Introduction (Cont.) Availability: Availability is defined as the probability that the unit is performing its intended function at a particular given time when used under an stated operating condition. It is proportion of time during which during which an equipment is available for use. =  

6. Failure & Failure Mode A failure is the partial or total loss or change in the properties of a device in such a way that its functioning is seriously impeded or completely stopped. Failures can be grouped in the following categories: Initial Failure or Infant Mortality. Wear-out Failure Random or catastrophic failure.

7. Types of Failure Initial Failure or Infant Mortality These defects are due to manufacturing defects, such as weak parts, poor insulation, bad assembly, poor fits. Large number of failure likely to occur during this period. Also known as debugging or burn –in period. In this period, failure rate decreases with time.

8. Types of Failure Wear-out failure These failures occur due to deterioration of the machine parts. Gradual change in the parameter become beyond the admissible limit. The changes are irreversible in nature. In this period, failure rate increases

9. Types of Failure Random or catastrophic failure These failures occur due to the sharp change in the parameters determining the performance of the system. These may occur due to change in environmental condition. Also known as the random failures or catastrophic failure, as these failures are difficult to detect. In this period, failure rate almost remain constant.

10. Bathtub Curve

11. Causes of Failures Poor Design Wrong Manufacturing Techniques Lack of knowledge and expertise Complexity of equipment Poor maintenance policy Organizational rigidity Human error