Design Project .docx

Banha University Faculty of Engineering-Shoubra Mechanical Production Department

Reliability & Failure analysis

BY: Abdullah Omar Mohammed Abou Reasha

Under the supervision of: Prof. Dr.atti gomaa

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The importance of Reliability Electrical, electronic and Mechanical equipment is used in a number of fields — in industry for the control of processes, in computers, in medical electronics, atomic energy, in weapon systems, defence equipments, communications, navigation at sea and in the air, and in many other fields. It is essential that this equipment should operate reliably under all the conditions in which it is used. In the air navigation, military and atomic energy fields, for instance, failure could result in a dangerous situation. Very complicated systems, involving large numbers of separate units, such as avionic and aerospace electronic systems are coming into use more and more. These systems are extremely complex and use a large number of component parts. As each individual part is liable to failure, the overall reliability will 2|Page

decrease unless the reliability of each component part can be improved.

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Reliability engineering

is an engineering field that deals with the study, evaluation, and life-cycle management of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time

Reliability engineering is a sub-discipline within systems engineering. Reliability is often measured as probability of failure, frequency of failures, or in terms of availability, a probability derived from reliability and maintainability. Maintainability and maintenance are often important parts of reliability engineering.

Well-publicized system failures such as those listed below may have also contributed to more serious consideration of reliability in product design •

Space Shuttle Challenger Disaster: This debacle occurred in 1986, in which all crew members lost their lives. The main reason for this disaster was design defects.

• Chernobyl Nuclear Reactor Explosion: This disaster also occurred in 1986, in the former Soviet Union, in which 31 lives were lost. This debacle was also the result of design defects.

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• Point Pleasant Bridge Disaster: This bridge located on the West Virginia/ Ohio border collapsed in 1967. The disaster resulted in the loss of 46 lives and its basic cause was the metal fatigue of a critical eye bar.

RELIABILITY SPECIALIZED AND APPLICATION AREAS

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Mechanical reliability

This is concerned with the reliability of mechanical items. Many textbooks and other publications have appeared on this topic. Example:

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Critical mechanical component assessment

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Shaft strength

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Selection of flexible couplings and transmission brakes

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Gear life assessment; screening of belt drives

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Assessment of bearing life, load ratings of slider bearings and shaft sealing devices

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Bolt loading and lubrication systems

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Software reliability.

This is an important emerging area of reliability as the use of computers is increasing at an alarming rate.

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Human reliability. In the past, many times systems have failed not due to technical faults but due to human error. The first book on the topic appeared in 1986

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Reliability optimization. This is concerned with the reliability optimization of engineering systems

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Reliability growth. This is basically concerned with monitoring reliability growth of engineering systems during their design and development

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Structural reliability. This is concerned with the reliability of engineering structures, in particular civil engineering Power system reliability.

This is a well-developed area and is basically concerned with the application of reliability principles to conventional power 5|Page

system related problems. Many books on the subject have appeared over the years including a vast number of other Robot reliability and safety. This is an emerging new area of the application of basic reliability and safety principles to robot associated problems  Life cycle costing. This is an important subject that is directly related to reliability. In particular, when estimating the ownership cost of the product, the knowledge regarding its failure rate is essential.  Maintainability.  This is closely coupled to reliability and is concerned with the maintaining aspect of the product.

TERMS AND DEFINITIONS •

Reliability: This is the probability that an item will carry out its assigned mission satisfactorily for the stated time period when used under the specified conditions.

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Failure: This is the inability of an item to function within the initially defined guidelines.

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 MEAN TIME BETWEEN FAILURES(MTBF): The mean exposuretime between consecutive failures of a component. This applies to repairable items, and means that if an item fails, say 5 times over a period of use totaling 1000hours, the MTBF would be 1000/5 or 200hours. 

 MEAN TIME BETWEEN MAINTENANCE (MTBM): The average time between all maintenance events that cause downtime, both preventative and corrective maintenance, and also includes any associated logistics delay time. 

 MEAN TIME TO FAILURE (MTTF): Mean Time To Failure (MTTF): Itis the average time that elapses until a failure occurs. MTTF is commonly found for non repairable items such as fuses or bulbs, etc.

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