Summary
Failure rate is the frequency with which an engineered system or component fails, expressed in failures per unit of time. It is usually denoted by the Greek letter λ (lambda) and is often used in reliability engineering. The failure rate of a system usually depends on time, with the rate varying over the life cycle of the system. For example, an automobile's failure rate in its fifth year of service may be many times greater than its failure rate during its first year of service. One does not expect to replace an exhaust pipe, overhaul the brakes, or have major transmission problems in a new vehicle. In practice, the mean time between failures (MTBF, 1/λ) is often reported instead of the failure rate. This is valid and useful if the failure rate may be assumed constant – often used for complex units / systems, electronics – and is a general agreement in some reliability standards (Military and Aerospace). It does in this case only relate to the flat region of the bathtub curve, which is also called the "useful life period". Because of this, it is incorrect to extrapolate MTBF to give an estimate of the service lifetime of a component, which will typically be much less than suggested by the MTBF due to the much higher failure rates in the "end-of-life wearout" part of the "bathtub curve". The reason for the preferred use for MTBF numbers is that the use of large positive numbers (such as 2000 hours) is more intuitive and easier to remember than very small numbers (such as 0.0005 per hour). The MTBF is an important system parameter in systems where failure rate needs to be managed, in particular for safety systems. The MTBF appears frequently in the engineering design requirements, and governs frequency of required system maintenance and inspections. In special processes called renewal processes, where the time to recover from failure can be neglected and the likelihood of failure remains constant with respect to time, the failure rate is simply the multiplicative inverse of the MTBF (1/λ).
About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related publications (1)

Capacité portante de ponts en arc en maçonnerie de pierre naturelle

Alix Grandjean

Historical masonry arch bridges are an integral part of our cultural heritage and deserve the attention and the efforts required to safeguard their patrimonial value. There is currently a diverse rang
EPFL2010
Related units

No results

Related concepts (13)
Failure rate
Failure rate is the frequency with which an engineered system or component fails, expressed in failures per unit of time. It is usually denoted by the Greek letter λ (lambda) and is often used in reliability engineering. The failure rate of a system usually depends on time, with the rate varying over the life cycle of the system. For example, an automobile's failure rate in its fifth year of service may be many times greater than its failure rate during its first year of service.
Reliability engineering
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).
Mean time between failures
Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system. The term is used for repairable systems while mean time to failure (MTTF) denotes the expected time to failure for a non-repairable system. The definition of MTBF depends on the definition of what is considered a failure.
Show more
Related courses (9)
CIVIL-522: Seismic engineering
This course deals with the main aspects of seismic design of buildings and bridges. It covers different structural design and evaluation philosophies for new and existing reinforced concrete and unrei
CS-487: Industrial automation
This course consists of two parts:
  1. architecture of automation systems, hands-on lab
  2. handling of faults and failures in real-time systems, including fault-tolerant computing
Show more
Related lectures (129)
Failure Modes in MicroNanosystems: Understanding Fatigue and Fracture Strength
Explores fatigue and fracture strength in MicroNanosystems, covering fluctuating loads, endurance limits, and temperature effects.
Reliability of Space Systems
Explores reliability and redundancy in space systems, including failure rates and safety design concepts.
Prestressed Bolted Assemblies
Explains the design and behavior of prestressed bolted assemblies, covering resistances, torques, and failure types.
Show more
Related MOOCs (2)
The Art of Structures I - Cables and arcs
Ce cours présente les principes du fonctionnement, du dimensionnement et de la conception des structures. L'approche est basée sur une utilisation de la statique graphique et traite en particulier des
The Art of Structures I - Cables and arcs
L'art des structures propose une découverte du fonctionnement des structures porteuses, telles que les bâtiments, les toitures ou les ponts. Ce cours présente les principes du dimensionnement et les s