Reliability engineering
1. History and Evolution of Reliability Engineering:
- Term ‘reliability’ traced back to 1816 by Samuel Taylor Coleridge
- Pre-World War II focus on repeatability for reliability
- Development of reliability engineering linked with quality improvement
- Significant applications in military equipment during World War II
- Establishment of reliability standards and societies in the mid-20th century
- Emphasis on reliability testing increased in the 1960s
- Shift towards understanding the physics of failure in the 1990s
- Introduction of qualitative approaches to reliability, such as the CMM model
2. Objectives and Challenges in Reliability Engineering:
- Reliability defined as product performance meeting customer expectations
- Reliability engineering aims to prevent failures and improve reliability
- Identifying and correcting causes of failures is crucial
- Methods for estimating new design reliability are essential
- Reliability is affected by stochastic parameters and uncertainties
- Prediction and measurement of reliability face significant challenges
- Focus on costs of failure in terms of system downtime and maintenance
- Reliability plays a crucial role in the cost-effectiveness of systems
3. Reliability Program Plan and Development:
- A reliability program plan is a complex learning and knowledge-based system
- Supported by leadership and built on skills developed within a team
- Integrated into business processes and executed following standard work practices
- Development of the plan is essential for achieving high levels of reliability, testability, and maintainability
- Specifies tasks for reliability engineers and other stakeholders
- Approval by top program management is necessary for sufficient resource allocation
4. Reliability Techniques, Analysis, and Requirements:
- Techniques include fault tree analysis, reliability-centered maintenance, and load/material stress calculations
- Proper analysis is crucial for effectiveness of reliability techniques
- Reliability tasks are specified in a program plan based on varying reliability requirements
- Reliability requirements drive design to prevent failures and limit consequences
- Specify reliability and maintainability requirements in system specifications, test plans, and contracts
- Maintainability requirements address repair costs and time, while testability requirements link reliability and maintainability
5. Human Factors, Design Strategies, and Reliability Prediction Challenges:
- Humans can detect failures, correct them, and improvise
- Design for Reliability (DfR) is a proactive process in product design
- Physics of Failure approach focuses on understanding physical failure mechanisms
- Reliability engineers rely on language to pinpoint risks and solve issues
- Predicting reliability quantitatively can be difficult and costly
- Reliability prediction should be used cautiously, primarily for comparison in trade-off studies
- Modifications to unreliable items can affect reliability predictions
- Reliability hazards classification involves classifying and ordering hazards based on qualitative and quantitative logic
Reliability engineering is a sub-discipline of systems engineering that emphasizes the ability of equipment to function without failure. Reliability describes the ability of a system or component to function under stated conditions for a specified period of time. Reliability is closely related to availability, which is typically described as the ability of a component or system to function at a specified moment or interval of time.
The reliability function is theoretically defined as the probability of success at time t, which is denoted R(t). In practice, it is calculated using different techniques and its value ranges between 0 and 1, where 0 indicates no probability of success while 1 indicates definite success. This probability is estimated from detailed (physics of failure) analysis, previous data sets or through reliability testing and reliability modeling. Availability, testability, maintainability and maintenance are often defined as a part of "reliability engineering" in reliability programs. Reliability often plays the key role in the cost-effectiveness of systems.
Reliability engineering deals with the prediction, prevention and management of high levels of "lifetime" engineering uncertainty and risks of failure. Although stochastic parameters define and affect reliability, reliability is not only achieved by mathematics and statistics. "Nearly all teaching and literature on the subject emphasize these aspects, and ignore the reality that the ranges of uncertainty involved largely invalidate quantitative methods for prediction and measurement." For example, it is easy to represent "probability of failure" as a symbol or value in an equation, but it is almost impossible to predict its true magnitude in practice, which is massively multivariate, so having the equation for reliability does not begin to equal having an accurate predictive measurement of reliability.
Reliability engineering relates closely to Quality Engineering, safety engineering and system safety, in that they use common methods for their analysis and may require input from each other. It can be said that a system must be reliably safe.
Reliability engineering focuses on costs of failure caused by system downtime, cost of spares, repair equipment, personnel, and cost of warranty claims.
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