Design for Reliability Flashcards

Environmental Stress Screening (ESS) differs from HALT primarily in that ESS:

Answer: Applies stresses within or near operational limits to precipitate latent manufacturing defects in production units

ESS applies thermal cycling and vibration stresses near operational limits on production units to precipitate latent manufacturing defects, whereas HALT uses much higher stresses to find design weaknesses.

In Design for Maintainability, which metric measures the probability that a failed system will be restored to operational status within a given time?

Answer: Maintainability (M(t))

Maintainability M(t) is defined as the probability that a failed item will be restored to a specified condition within a given time when maintenance is performed under stated conditions.

A system has two identical components in active parallel redundancy, each with reliability R. What is the system reliability?

Answer: 1 - (1 - R)²

For two components in active parallel redundancy, system reliability = 1 - (probability both fail) = 1 - (1-R)², which is always greater than R for R > 0.

Which concept in Design for Reliability refers to using the same standardized components across multiple products or subsystems to reduce the variety of parts?

Answer: Parts standardization and commonality

Parts standardization and commonality reduce the variety of components used, improving procurement, simplifying maintenance, lowering inventory costs, and accumulating more reliability data per part type.

Built-In Test Equipment (BITE) is incorporated into a design primarily to:

Answer: Automatically detect, isolate, and report faults to reduce diagnostic time and improve availability

BITE is embedded diagnostic hardware/software that automatically detects and isolates failures, reducing mean time to diagnose (MTTD) and improving overall system availability.

Reliability Growth testing (e.g., using the Duane model or AMSAA model) is conducted to:

Answer: Track and improve reliability iteratively by finding and fixing failures during a structured test-analyze-fix-test (TAFT) cycle

Reliability Growth programs use a test-analyze-fix-test (TAFT) cycle where failures are identified, root causes analyzed, and corrective actions implemented to continuously improve reliability over time.

The concept of 'functional partitioning' in Design for Reliability involves:

Answer: Dividing the system into modules based on functional boundaries to contain fault propagation and simplify isolation

Functional partitioning organizes a design into discrete functional modules so that failures are contained within boundaries, simplifying fault isolation, maintenance, and replacement.