What is the most popular reliability test

2022-08-06
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What is reliability testing

reliability test is a means to investigate, analyze and evaluate the reliability of products. The test results provide a basis for fault analysis, study of corrective measures taken, and judgment of whether the product meets the index requirements. The specific purposes are:

1 to find various defects in product design, components, parts, raw materials and processes

2 provide information for improving the integrity of products, improving the success of tasks, and reducing maintenance manpower costs and support costs

3 confirm whether it meets the reliability quantitative requirements

in order to achieve the above purpose, laboratory test or field test can be carried out according to the situation

the laboratory test is a simulation test in a certain way. The test profile should try to conform to the environmental profile that the oil collector using the oil pump is not pressed on the pump body and can only reach a certain load each time it is loaded. However, it is not restricted by the site and can be carried out at all stages of product development, development, production and use. It has the characteristics of typicality of environmental stress, accuracy of data measurement, integrity of records, etc. Through the test, we can continuously deepen the understanding of product reliability, and provide basis and verification for improving product reliability

field test is the test of the product on the use site. The test profile is real but uncontrolled, so it is not typical. Therefore, it is necessary to record and analyze the impact of environmental conditions, measurement, failure, maintenance and other factors on the site. Even so, it is still difficult to obtain timely reliability evaluation information from the site test. Unless several equipment are placed on the site for use until they are worn out, it is possible to accurately evaluate their reliability after faithfully recording the failure information. When the system is large and difficult to test in the laboratory, the field reliability test of prototype and small batch products is of great significance

2 classification of reliability test

2.1 failure distribution during the life of electronic equipment

at present, we believe that the typical failure distribution during the life of electronic equipment conforms to the "bathtub curve", which can be divided into three sections: early failure section, constant (random or accidental) failure section and loss failure section. Refer to figure 2.1

early failure stage, also known as early failure stage. Early failure occurs in the early period of the product life. The early failure period begins when the product is assembled. Its characteristic is that the failure rate is high and rapidly decreases with the increase of working time. Early failures are mainly caused by the exposure of manufacturing process defects and design defects, such as poor insulation caused by raw material defects, faulty welding caused by welding defects, parameter drift caused by improper assembly and adjustment, performance failure caused by component defects, etc. Early failures can be exposed and eliminated by strengthening the inspection of raw materials and components, process inspection, environmental stress screening at different levels and other strict quality management measures

early wear and tear

failure accidental failure section failure

figure 2.1 bathtub curve diagram of failure distribution during the life of electronic equipment

constant failure section, also known as accidental failure section, its failure is caused by random failure of internal components and parts of the equipment, which is characterized by low failure rate and relatively stable, so it is the main working period of the equipment

The

depletion failure section is characterized by a rapid rise in the failure rate, resulting in a sharp increase in maintenance costs and thus scrapping. The failure is mainly caused by wear, fatigue, aging and loss of structural parts and components

2.2 change of test type and its distribution curve

for the three stages of life-cycle failure distribution of electronic equipment, people take targeted measures when designing, manufacturing and using equipment to improve reliability and reduce life-cycle cost. In the design and manufacturing stage, design defects and manufacturing defects should be minimized. Even so, there will still be early failure and random failure. Therefore, the manufacturer needs to use the means of engineering test to expose and eliminate early failure and reduce the inherent level of random failure. Through these measures, the shape of the product life distribution curve can be changed, as shown in Figure 2.2. In the wear and tear stage, users can extend the service life of equipment by means of maintenance and local renewal

Figure 2.2 shows the life failure rate distribution curve of two groups of products. The figure shows that the reliability level of product B is better than that of product a, because the constant failure rate of product B is lower than that of product a, and the early failure period of product B is shorter than that of product a. If curves a and B are the distribution of failure rates at different stages of the same product, it indicates that the product has passed the reliability growth test and achieved results. Therefore, the constant failure rate of curve B is greatly reduced. The early failure section of curve B shows two lines B and B ', which show that the early failure rate of B is lower than that of B', showing that the defects of process, components and raw materials are less than that of B ', and the resources required for environmental stress screening can also be less

life failure distribution of product a

b life failure distribution of product B

Figure 2.2 effect of equipment reliability test results on the shape of failure distribution curve

2.3 equipment reliability test classification

2.3.1 equipment reliability test item classification

based on the purpose of equipment reliability test, we divide it into two categories: reliability engineering test and reliability verification test, and each type of test includes several test items

1 reliability engineering test aims to expose product faults so that people can eliminate them. It is carried out by the manufacturer, and the test samples are obtained from the developed prototype. Reliability engineering test includes environmental stress screening and reliability growth test. From the test nature, the current aging is also an engineering test item; The reliability guarantee test developed from environmental stress screening can also be summarized here. The starting point of the engineering test is to thoroughly expose the problems and defects of the product as far as possible, take measures to correct them, and then verify whether the problems and defects have been solved and eliminated. After engineering tests, the reliability of products will naturally improve, and the possibility of meeting user requirements will inevitably increase. It can be seen that reliability engineering test is the basic work of product reliability and the technological process of product development and production

2 reliability verification test, from the test principle, should apply statistical sampling theory, so it is also called statistical test. The purpose is to verify whether the product meets the specified reliability requirements. The manufacturer shall formulate a scheme and plan according to relevant standards and development and production progress, which shall be approved by the ordering party; The verification test scheme of key model equipment shall also be submitted to the superior leading authority for approval, and the relevant parties shall organize a joint test team. The verification test includes the reliability identification test of product development and the reliability acceptance test of mass production. Such tests must be able to reflect the quantitative level of equipment reliability, so the test conditions should be as close to the environmental stress as possible; The acceptance or rejection judgment shall be made for the test results. Therefore, the test time and faults shall be recorded in detail. The final conclusion can be made only after the comparison and analysis with the failure criteria and the unified understanding of all parties to the test

2.3.2 differences between equipment reliability test and additional test items of short-distance electric transport terminal

table differences between environmental stress screening, environmental qualification test and reliability statistical test

project environmental stress screening, environmental qualification test, reliability statistical test

application purpose accelerate the development of potential defects of products into faults, eliminate and verify the environmental adaptability of products, verify the reliability level of products

typical stress random vibration,

temperature cycle, electrical stress temperature, humidity, salt fog, rain, mold Vibration, impact, low air pressure, acceleration temperature, humidity, vibration,

stress levels strengthen stress, which can not only expose faults but also do not damage the extreme values of the product's environmental conditions, dynamically simulate the real environmental conditions

stress procedures are combined according to the effect, General: vibration temperature vibration simulates the order of use according to the order of use or the order that can respond to the maximum environmental stress.

100% sampling of samples

fault limits hope to reveal that the fault samples can be repaired and there is no limit on the number of faults.

the acceptance criteria is none. Measuring individual composite particles on the injection machine adds one layer of complexity. The fault does not affect the product reception. The fault affects the product reception, Reject if the number of faults exceeds the specification

3 test arrangement

when arranging the test plan, the reliability test shall be combined with the performance test, environmental stress and durability test as much as possible to form a comprehensive reliability comprehensive test plan. In this way, repeated tests can be avoided, problems and defects easy to be neglected in separate tests can not be omitted, and efficiency can be improved to save costs. Www. reliability.Com

1 the product performance test shall be conducted immediately after the prototype is manufactured, and the defects exposed in the test shall become the direct basis for improvement measures. To evaluate whether the product performance and reliability meet the user's requirements, the performance measurement must be carried out under standard environmental conditions using the specified tolerance values to obtain the reproduction results and the required accuracy

the performance before (standard condition), during (test condition) and after (standard condition) test shall be measured and recorded respectively for comparison

2 the types of environmental stress should be integrated according to the actual situation. Environmental stress shall at least include heat, vibration, humidity and other stresses; The humidity level in the temperature cycle shall be sufficient to produce obvious condensation and frost; Vibration stress shall consider such factors as vibration type, frequency range, stress size, application method and vibration direction. All these shall be similar to the conditions generated by the site use environment and task profile

3 durability test generally includes environmental test, overload test and cyclic test simulating or close to environmental profile. All problems occurred in the test shall be analyzed and corrective measures shall be taken. Then test the improved product to prove whether the problem has been solved

4 test evaluation

4.1 evaluation of test conditions

the test conditions, steps and methods should simulate the life profile and task profile of the product as much as possible to make the test authentic. The purpose of the test is to expose the problems, faults and defects that can only occur in the service environment. If the test can only expose some problems, it is a waste of time and resources. The degree of test simulation depends on the purpose of the test

1 the reason for the low authenticity of the test may be the neglect of some stresses. For example, the connector ignores the vibration stress during the static life test, resulting in frequent failures during field use

2 for the test of exposed defects, it is also appropriate that the applied stress is higher than the service stress. "Over stress" test is generally used for engineering reliability test, such as aging test, screening, reliability growth test in development stage, etc. These are the characteristics of accelerated test, which can expose the hidden weak links of the product as soon as possible and take measures to correct them

It is hoped that the reliability obtained from the test is consistent with the reliability in use. However, the simulated conditions are always different from the real conditions. In most cases, the life test under constant stress condition is not effective. Therefore, it is necessary to design the test profile of the cycle period of comprehensive stress to make it closer to the service conditions

4.2 equipment reliability evaluation