CRE Design for Reliability 3

Question 1

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

Accepted Answer

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

Answer

Uses higher stress levels to find design defects, while HALT only reveals manufacturing defects

Answer

Is performed exclusively during the design phase before any hardware is built

Answer

Is used only to validate compliance with environmental specifications like MIL-STD-810

Question 2

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

Accepted Answer

Maintainability (M(t))

Answer

Availability (A)

Answer

Mean Time To Repair (MTTR)

Answer

Mean Maintenance Man-Hours Per Repair (MMH/R)

Question 3

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

Accepted Answer

1 - (1 - R)²

Answer

R × R = R²

Answer

R + R = 2R

Answer

R / (2 - R)

Question 4

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

Accepted Answer

Parts standardization and commonality

Answer

Modular design

Answer

Design simplification

Answer

Functional partitioning

Question 5

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

Accepted Answer

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

Answer

Replace periodic scheduled maintenance tasks entirely

Answer

Increase the complexity of the design to meet military specifications

Answer

Serve as a redundant backup for critical system functions

Question 6

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

Accepted Answer

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

Answer

Demonstrate that a mature product meets its MTBF specification at the end of development

Answer

Qualify components to MIL-PRF standards before system integration

Answer

Establish the steady-state failure rate for use in FMEA occurrence ratings

Question 7

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

Accepted Answer

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

Answer

Assigning reliability requirements to individual components proportionally by cost

Answer

Partitioning the failure mode database between hardware and software teams

Answer

Splitting redundant paths across different physical locations to reduce common cause exposure