Reliability is also called reliability, which refers to the ability of a product to complete a predetermined function within a specified time and under specified conditions. It includes the safety, applicability and durability of the structure. When measured by probability, it is called reliability·
Reliability: the ability of the product to complete the specified functions under the specified conditions and within the specified time.The probability measure of reliability is called reliability[1]。
Life refers to the duration of product use.Measured in Life Units.Under the specified conditions and within the specified time, the ratio of the total number of product failures to the total number of life units is called "failure rate".Failure rate is the basic reliability parameter, and its reciprocal is the mean time between failures (MTBF)[1]。
Reliability is divided into inherent reliability and service reliability.The inherent reliability is used to describe the reliability level of product design and manufacturing. The operational reliability comprehensively considers the factors such as product design, manufacturing, installation environment, maintenance strategy and repair.From the perspective of design, reliability is divided into basic reliability and task reliability. The former includes reliability related to maintenance and supply, and is expressed by mean time between failures (MTBF);The latter only considers the failure impact that causes task failure, which is expressed in terms of mission reliability (MR) and mission time between fatal failures (MTBCF).Most enterprises are mainly concerned with the inherent reliability and basic reliability of products.For repairable products, it is expressed as mean time between failures, for non repairable products, it is expressed as mean failure rate, and for disposable products, it is expressed as mean life[1]。
For products, the higher the reliability, the better.Products with high reliability can work normally for a long time (this is what all consumers need);In terms of technical terms, the higher the reliability of the product, the longer the product can work without failure.
Reliability analysis is the knowledge of calculating the operation probability of each system, such as the reliability of machines and tools, which will affect the process planning and control of the entire production and manufacturing.In addition, the discussion of reliability is often inseparable from the availability and maintainability of the system.Generally speaking, reliability refers to the reliability of products. As the name implies, it means that the quality of products is expressed in the way of reliability. This definition is very important for many products with high unit price and after-sales service.
classification
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Reliability can generally be divided into two levels. The first is the so-called reliability of component.That is, the product is disassembled into several different parts or components, and the reliability of these components is studied first, and then the overall reliability of the whole system and the whole product, that is, the reliability of the system.The method of component reliability analysis is actually statistical analysis. As for system reliability analysis, it is complicated and there are many available methods,
① Allocate reliability according to importance.
② Allocate reliability by complexity.
③ The reliability shall be allocated according to the comprehensive indicators such as technical level and task conditions.
④ The reliability is allocated according to the relative failure rate.
After each part has a clear reliability index, the design calculation of the parts is carried out according to different calculation criteria.The main calculation methods are: calculate the reliability or required size according to the distribution of load and strength;Calculate reliability or safe life according to the distribution of load and life;The quantitative relationship between reliability and safety factor is obtained, and the required size or safety factor is calculated by conventional design method.The load, strength, size, life and other data related to reliability design are all random variables, which must be treated with probability statistical methods.
mathematical expression
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The reliability function can be expressed as a function of time t, which can be expressed as
R（t）=P(T>t)
Where, t is the specified time, and T is the life of the product.
It can be seen from the definition of reliability that R (t) describes the probability that the product is intact within (0, t) time, and R (0)=1, R (+∞)=0.
Reliability engineering
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Reliability engineering is a science combining management and engineering technology. It involves three aspects of engineering technology: electronic (mechanical) engineering, mechanical engineering, and material engineering.There are few high-tech products that are not related to these three aspects.Only when reliability is essentially a quality assurance technology that applies statistical methods to various professional fields, and reliability is actually designed into products, can product quality be ensured.
Reliability test
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The test of product reliability index is reliability test.Reliability test includes environmental test, mechanical stress test, weather resistance test, function test, EMC and safety regulation test, etc.
Development of reliability engineering
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The embryonic stage: during World War II, Germany put forward the basic theory of system reliability in the development of V1 rockets, according to which the reliability of V1 rockets reached 75%.During the Korean War, 60% of the airborne electronic equipment of the United States could not be used after being transported to the Far East, and 50% of the electronic equipment failed during storage.The US Navy has 160000 or 70000 electronic equipment, and needs to replace 1 million electronic components every year. The replacement rate of electronic tubes is five times higher than other components.In 1943, the United States established the "Electron Tube Research Committee" to study the reliability of electron tubes. In 1949, the American Society of Radio Engineers established the Reliability Technology Group - the first reliability professional academic organization was born[1]。
The establishment stage of reliability engineering: in the 1950s, the United States found in the Korean War that unreliable electronic equipment affected the conduct of the war and required a large amount of maintenance costs. The annual maintenance costs were twice the equipment procurement costs!The military, manufacturing companies and academia are involved in reliability research.In December 1950, the United States established the "Special Committee on Reliability of Electronic Equipment", and by March 1952, it had put forward far-reaching recommendations[1]：
Overall development stage of reliability engineering: in the 1960s, with the rapid development of aerospace industry, reliability design and test methods were accepted and applied to avionics systems, and reliability engineering developed rapidly[1]。It is mainly manifested in:
The reliability management was improved and a reliability research center was established. The United States issued the Outline Requirements for Reliability of Systems and Equipment in 1965. Reliability engineering activities were combined with traditional design, development and production, and good benefits were obtained.The Roma Aviation Development Center has established a reliability analysis center, which is engaged in the reliability research of electronic and electromechanical, mechanical parts and electronic systems related to electronic equipment, including reliability prediction, reliability distribution, reliability test, reliability physics, reliability data acquisition, analysis, etc[1]。
Formulate reliability test standards and develop reliability test methods.Mainly studied and designed the statistical test plan and sampling plan, and issued the Failure Rate Sampling Plan and Procedure, Reliability Test, Exponential Distribution (revised to Reliability Design Qualification Test and Product Acceptance Test (Exponential Distribution) in 1967), Life and Reliability Test Sampling Procedure and Table, etc[1]。
Develop reliability prediction technology and issue reliability prediction manual standards.After collecting a large number of field and test failure data, the Electronic Equipment Reliability Prediction Manual was issued in 1962 and revised the following year to serve as the standard for quantitative reliability prediction of aircraft, missiles, satellites and electronic equipment at all stages of development[1]。
An effective data system has been established.The data acquisition system, reliability data center, and security center were successively established in the US military and scientific research institutions, and a national data exchange network was formed in 1966[1]。
Pay attention to maintainability research.In the 1950s, the United States spent 9 billion dollars annually on weapon system maintenance, accounting for 1/4 of the national defense budget.At the end of the 1950s, the Roma Aviation Development Center started a three-year maintainability research plan to study the factors affecting maintenance and develop maintainability verification and prediction technologies.In 1966, the Maintainability Outline Requirements, Maintainability Identification, Verification and Evaluation, Maintainability Prediction and other standards were issued[1]。
Various countries have successively carried out comprehensive reliability engineering research.In the early 1960s, the Soviet Union took technical and organizational measures to promote the development of reliability engineering. In 1962, it published a more complete textbook, Statistical Methods for Reliability and Quality Control, and established a reliability organization led by the chief engineer and related laboratories. The research results of K-S statistical test method and Markov process are internationally recognized,Redundancy technology, derating technology, improving raw materials and special circuits are adopted to ensure the reliability of products and make up for the shortcomings of electronic components.They quoted a lot of American military standards for reliability.The reliability project in France emphasizes centralized management, attaches importance to the reliability research of components, and establishes the "Telecommunication Commission" to coordinate the reliability requirements of various departments on electronic components.The central acceptance test system shall be established, and the manufacturer shall conduct reliability acceptance tests on batch production products under the supervision of the Telecommunication Commission to save money.In 1962, a reliability center was established in the National Telecommunication Research Center, which is responsible for collecting, synthesizing, publishing reliability data, collecting, analyzing, processing and distributing reliability data, and studying reliability test methods[1]。
The in-depth development stage of reliability engineering: in the 1970s, the problem of life cycle cost of the US defense weapon system was prominent, and people more deeply realized that reliability engineering was an important tool to reduce life cost, which was further developed and increasingly mature.The characteristics of the stage are: 1 Establish a unified reliability management organization.2 Establish a national unified reliability data exchange network.3 Improve reliability design and test methods.More rigorous, practical and effective design and test methods were adopted.The failure physics research and analysis technology has been developed, such as FMEA developed into FMECA.More stringent derating design[1]。
The development of reliability engineering in China: early introduction, solid quotation and vitality.In the early 1960s, the Ministry of Electronics established the "China Electronic Product Reliability and Environment Test Institute", which carried out pioneering work in reliability assessment.In 1965, at the suggestion of Qian Xuesen, a scientist, 7 Machinery Department established the Reliability Quality Management Institute.Aerospace products adopt strictly screened "seven special" components.In the mid-1970s, due to the needs of Sino Japanese submarine cables, the Ministry of Electronics carried out verification tests for highly reliable components and developed the accelerated life test technology.Since the late 1970s, many universities have held reliability learning classes to train in-service personnel. Later, reliability courses have been opened to recruit undergraduate and graduate students.Since 1984, the organization has formulated, introduced and issued reliability and infinitesimal standards, forming a relatively complete system.Military enterprises have carried out reliability remedial work and product reliability growth work. The military has carried out reliability assessment and analysis work, and 5 institutes of the Ministry of Electronics have established reliability data centers[1]。
The prospect of reliability engineering: the reform and opening up, the establishment of modern enterprise system, so that the competition between countries extends to the competition between enterprises, reliability engineering also develops rapidly, mainly reflected in the change of concept.The concept of enterprise leaders has changed from "I should attach importance to reliability engineering" in the past to "I should attach great importance to reliability engineering" now.Reliability engineering has been widely accepted by the society, and universities have listed reliability theory and technology as professional basic courses for many majors.Reliability knowledge will become people's basic common sense.Many products have clear reliability quantitative indicators and important advertising words[1]。
Reliability engineering has developed from military enterprises to civil electronic information industry, transportation, service, energy and other industries, and from specialty to "general industry".In the ISO certification process of the quality management system, reliability management is taken as an important part of the review.Professional and technical standards related to reliability have been reorganized and incorporated into the quality management system documents, becoming the management provisions of "what is said must be done"[1]。
In terms of reliability technology, it has developed very rapidly.From 1992 to October 2003, the Shenzhou 5 manned spacecraft successfully completed its mission, with a total investment of 19 billion yuan.The carrying capacity of the spaceship is 3 people, 300 kg and 7 days.The reliability is 0.97, and the safety is 0.997.The design has the ability of independent fault judgment and independent function reorganization. Even if it is hit and broken in space, the cabin pressure can still be maintained for 15 minutes to ensure the time for astronauts to change their spacesuits.A total of 110 institutes participated in the research and development, and more than 3000 units participated in product manufacturing.A total of one sample, four normal samples and five launch vehicles were produced.The diameter of Shenzhou 5 spaceship is 2.5 meters. There are more than 600 instruments, 100000 components and 80000 contacts on it. There are 700000 programs in the software, 20% of which are used for normal operation, and the rest are used for disposal in case of failure.Eight failure modes are designed in the launching and rising section, and 108 failure modes are designed in the operation and recovery section[1]。
