Reliability engineering is crucial in product development, focusing on equipment functioning without failure. It addresses reliability, availability, maintainability, and safety throughout a product's lifecycle. From design to service, it ensures products meet reliability requirements and maintain performance in the field.

This topic connects to the broader chapter on engineering applications by showcasing how statistical techniques are applied in real-world scenarios. It demonstrates how engineers use tools like FMEA, reliability testing, and maintenance strategies to improve product reliability and safety in various industries.

Reliability Engineering in Product Development

Role of Reliability Engineering

• Reliability engineering is a subspecialty of systems engineering that emphasizes the ability of equipment to function without failure
• Focuses on four key elements: reliability, availability, maintainability, and safety (RAMS)
• Identifies and manages asset reliability risks that could adversely affect plant or business operations
• The primary role is to identify and manage asset reliability risks that could adversely affect plant or business operations
• Important in all phases of the product lifecycle, from design and development through testing, manufacturing, and service life

Importance Throughout Product Lifecycle

• Reliability engineering is critical during the design and development phase to ensure the product is designed for reliability from the start
  • Involves selecting reliable components, designing redundancy and fault tolerance into the system, and conducting reliability analyses
• During testing, reliability engineering helps validate the reliability of the product through various testing methods (accelerated life testing, HALT, stress-strength analysis)
• In manufacturing, reliability engineering ensures the production processes are capable of consistently producing products that meet the reliability requirements
• Throughout the service life of the product, reliability engineering supports maintenance and repair activities to sustain the reliability of the product in the field
  • Includes developing preventive maintenance schedules, troubleshooting guides, and spare parts provisioning

Failure Modes and Effects Analysis

FMEA Process

• Failure mode and effects analysis (FMEA) is a step-by-step approach for identifying all possible failures in a design, a manufacturing or assembly process, or a product or service
• A common process analysis tool used in reliability engineering to identify potential failure modes, determine their effect on the operation of the product, and identify actions to mitigate the failures
• The purpose is to take actions to eliminate or reduce failures, starting with the highest-priority ones
  1. Identify potential failure modes
  2. Assess the severity, occurrence, and detection of each failure mode
  3. Calculate the risk priority number (RPN) for each failure mode
  4. Develop action plans to mitigate the high-priority failure modes
  5. Implement the actions and re-assess the RPN

Statistical Techniques in FMEA

• Key statistical techniques used in FMEA:
  • Pareto analysis to identify the most common failures
    • Helps prioritize which failure modes to address first based on their frequency of occurrence
  • Weibull analysis to model time-to-failure and predict reliability over time
    • Estimates the probability of a failure occurring within a specific timeframe
• Fault tree analysis (FTA) is another technique used to analyze the undesired states of a system using boolean logic to combine a series of lower-level events
  • Starts with a top event (system failure) and works backward to identify all the possible ways the failure could occur
  • Uses logical gates (AND, OR) to show the relationship between events

Reliability Testing Methods

Types of Reliability Tests

• Reliability testing is the process of testing a system or component under stated conditions for a specified period of time to determine the probability that it will perform its intended function adequately for the specified period of time, under the specified environmental conditions
• Accelerated life testing uses increased stress levels to shorten the life of the product or quicken the degradation of the product's performance to obtain reliability data more quickly
  • Common stresses include temperature, voltage, vibration, and humidity
• Highly accelerated life testing (HALT) is a stress testing methodology used to expose design and process weaknesses, allowing engineers to improve them prior to product launch
  • Applies a combination of stresses (thermal cycling, vibration, voltage margining) to rapidly find weaknesses
• Stress-strength analysis is a methodology used to assess the reliability of a component or system in terms of the stress it experiences and its ability to resist that stress (its strength)
  • Estimates the probability that the strength exceeds the stress
• Degradation testing is used to measure the performance of a product over time under normal operating conditions to estimate its expected lifetime under those conditions
  • Tracks key performance parameters (output voltage, flow rate, etc.) over time to model the degradation

Analyzing Reliability Test Data

• Reliability test data is analyzed using statistical methods to estimate key reliability metrics:
  • Mean time to failure (MTTF) for non-repairable systems
  • Mean time between failures (MTBF) for repairable systems
  • Failure rate over time (bathtub curve)
  • Probability of failure within a specific time (reliability function)
• Confidence intervals are used to quantify the uncertainty in the reliability estimates based on the sample size and variability of the test data
• Acceleration factors are used to extrapolate the reliability estimates from the accelerated test conditions to the normal use conditions
  • Arrhenius equation for temperature acceleration
  • Inverse power law for voltage and mechanical stress acceleration

Strategies for Reliability Improvement

Design for Reliability

• Reliability strategies focus on reducing the likelihood of failure through robust design, redundancy, and fault tolerance
  • Robust design involves selecting components and materials that are insensitive to variation in manufacturing and environmental conditions
  • Redundancy involves including backup components or systems that can take over if the primary component fails
  • Fault tolerance involves designing the system to continue operating, possibly at a reduced level, in the presence of faults
• Safety strategies focus on minimizing the consequences of failure through fail-safe designs, protective devices, and warning systems
  • Fail-safe designs ensure the system remains in a safe state in the event of a failure (elevator brakes)
  • Protective devices prevent unsafe conditions (pressure relief valves, circuit breakers)
  • Warning systems alert operators to unsafe conditions (alarms, fault indicators)

Maintenance and Logistics Support

• Maintainability strategies focus on reducing the time to repair or replace failed components through modularity, standardization, and diagnostic tools
  • Modularity involves designing the system as a set of easily replaceable modules to facilitate repair
  • Standardization involves using common components and interfaces to reduce the variety of spare parts and tools required
  • Diagnostic tools help technicians quickly identify and isolate faults to speed up repair time
• Availability strategies focus on maximizing the uptime of the system through preventive maintenance, condition-based maintenance, and rapid repair capabilities
  • Preventive maintenance involves regularly scheduled servicing and replacement of wear-out items to prevent failures
  • Condition-based maintenance involves monitoring the system for signs of impending failure and taking action before the failure occurs
  • Rapid repair capabilities involve having trained technicians, spare parts, and tools readily available to minimize downtime when failures do occur
• Reliability centered maintenance (RCM) is a process to ensure that systems continue to do what their users require in their present operating context by combining various maintenance strategies
  • Focuses maintenance resources on the most critical functions of the system
  • Utilizes preventive, predictive, and reactive maintenance tasks as appropriate based on the failure modes and consequences