Glossary

Technical terms explained clearly and concisely.

A reference for key terms from reliability engineering, lifetime, testing, DoE and technical risk management.

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A

Accelerated life testing (ALT): Testing under increased, physically justified stresses to observe failures sooner and transfer the results to use conditions with a suitable acceleration model.

B

B10 life: Time or usage by which ten percent of a population have statistically failed.
Bathtub curve: Conceptual failure-rate curve with early-life, useful-life and wear-out phases.
Bq life: Time or usage by which a fraction q of a population has failed; B10 life is the common special case with q = 10%.

C

Censored data: Observations for which the exact failure time is not fully known, for example because an item has not failed by the end of observation.
Confidence bound: One-sided or two-sided boundary of a confidence interval that expresses the uncertainty of a quantity estimated from sample data.
Confidence level: Predefined level of confidence, such as 90 or 95 percent, used by a statistical estimation or demonstration procedure.

D

Dependability: Ability of an item to perform as and when required; it encompasses reliability, maintainability, supportability and the resulting availability.
Design for Reliability (DfR): Engineering approach that integrates reliability into requirements and product development.
Design of Experiments (DoE): Statistical experimental design for efficient investigation of factors, interactions and responses.

E

Early-life failure: Failure at the beginning of use, often related to manufacturing, assembly or material defects.

F

Failure mechanism: Physical, chemical, electronic or software-related process that causes loss of function.
Failure Mode and Effects Analysis (FMEA): Systematic analysis of potential failure modes, causes, effects and actions.
Failure probability: Probability that an item fails by a specified time or amount of use; commonly denoted by F(t).
Failure rate: Time-dependent rate at which units in a population fail.
Fatigue failure: Failure caused by repeated or alternating mechanical loading.
Fault Tree Analysis (FTA): Deductive analysis that structures possible causes of an unwanted top event.
Field data analysis: Evaluation of operating, usage, failure and, where applicable, censored data from products in real-world service.

H

Health monitoring: Monitoring technical condition to detect changes and critical developments early.
Highly Accelerated Life Testing (HALT): Development method that exposes products step by step beyond their intended operating range to reveal design limits and hidden weak points; HALT is not a statistical lifetime demonstration.

L

Lifetime: Time, load cycles or use until a defined failure criterion is reached.
Lifetime analysis: Statistical and technical evaluation of failure times, censored data and operating conditions.
Lifetime model: Mathematical relationship between stress, time and failure behaviour.
Lifetime testing: Testing used to determine or demonstrate time- or usage-dependent failure behaviour under specified loads and failure criteria.
Load spectrum: Description of the magnitude, frequency, duration and sequence of loads experienced by a product during use.

M

Maintainability: Ability of a system to be maintained or restored under defined conditions.
Mean Time Between Failures (MTBF): Average operating time between successive failures of a repairable system.
Mean Time To Failure (MTTF): Average time to failure of a non-repairable item.
Mean Time To Repair (MTTR): Average time required to restore a repairable system.
Mission profile: Structured description of actual use and environmental conditions over time from which relevant loads and test conditions are derived.

P

Prognostics and Health Management (PHM): Methods for condition assessment, failure prediction and maintenance planning.

R

RAMS: Joint consideration of reliability, availability, maintainability and safety when assessing technical systems over their life cycle.
Reliability: Probability that a product performs its required function under defined conditions for a specified period.
Reliability assurance: Coordinated combination of analyses, simulations, testing and documentation used to justify fulfilment of defined reliability requirements.
Reliability Block Diagram (RBD): Logical representation of how component reliability influences system function.
Reliability demonstration: Documented technical or statistical evidence that a defined reliability target is met under specified conditions and at an agreed confidence level.
Reliability engineering: Engineering discipline covering reliability planning, analysis, testing, assurance and prediction.
Reliability planning: Definition, allocation and tracking of reliability targets, methods, responsibilities and evidence throughout product development.
Reliability target: Measurable requirement linking function, use conditions, duration and the permitted failure level of a product or system.
Risk assessment: Analysis and evaluation of technical risks by likelihood and consequence to establish priorities and suitable actions.
Risk management: Continuous process of identifying, assessing, treating and monitoring technical risks throughout the product life cycle.
Robustness: Ability of a product or process to meet requirements despite unavoidable variation in material, manufacturing, environment and use.
Root Cause Analysis (RCA): Structured investigation to identify the fundamental cause of a failure.

S

Sample: Selected subset of a population whose observations are used to draw conclusions about that population.
Stress screening: Loading process used to reveal latent manufacturing or assembly defects before field use.
System availability: Proportion of time for which a system is functional and ready for use.
System reliability: Reliability of the complete system resulting from its structure, dependencies, redundancies and the properties of its elements.

V

Validation: Confirmation by objective evidence that a product or system fulfils the requirements and needs of its intended application.
Verification: Confirmation by objective evidence that specified requirements or specifications have been fulfilled.

W

Wear-out failure: Failure caused by progressive ageing, wear or material degradation.
Weibull analysis: Statistical method for describing lifetime, variation and characteristic failure behaviour.