To measure, verify or improve the product reliability The test conducted is called reliability test, which is a product Reliability work Is an important link of. Generally, the purpose of reliability test on products is as follows:
(1) Make the product reach the predetermined reliability index in the development stage. In order to make the product reach the predetermined reliability index, reliability tests should be carried out on the samples in the development stage to find out the problems existing in the raw materials, structure, process, environmental adaptability and other aspects of the product, and make improvements. After repeated tests and improvements, the reliability indexes of the product can be continuously improved to meet the predetermined requirements.
(2) Reliability identification shall be carried out during product development and finalization. When new products are developed and finalized, identification tests shall be carried out according to product standards (or product technical conditions) to comprehensively assess whether the products meet the specified reliability indicators.
(3) Control the quality of products in the production process. In order to produce products stably, it is sometimes necessary to conduct reliability tests on each product according to the items specified in the product technical conditions. In addition, reliability sampling test shall be carried out batch by batch or according to a certain period. The stability of product quality can be understood through the reliability test of the product. If the product quality declines due to poor quality of raw materials or out of control process, it can be reflected in the reliability test of the product, so that corrective measures can be taken in time to restore the product quality to normal.
(4) The products are screened to improve the reliability level of the whole batch of products. Reasonable screening can combine various reasons (such as raw material The early failure products caused by defects, improper process measures, operator negligence, production equipment failure and poor quality inspection shall be eliminated, so as to improve the reliability level of the whole batch of products. (5) Study the failure mechanism of products. The reliability test (including simulation test and field use test) of the product can understand the failure mode and failure law of the product under different environments and stress conditions. The internal causes of product failure (i.e failure mechanism ）And the weak link of the product, so that corresponding measures can be taken to improve the reliability level of the product. [2] Reliability test can be divided into environmental test, life test, special test and field use test according to the project.
(1) Reliability environment test
This test includes many items, mainly including: ① climatic conditions, such as temperature, humidity, air pressure, snow, salt fog, corrosive gas, etc.; ② mechanical conditions, such as vibration, shock, centrifugation, collision, drop, weight loss, noise, shock wave, etc.; ③ radiation conditions, such as solar radiation, nuclear radiation Etc. (2) Life test
Life test is an extremely important part of reliability test. Through this test, we can understand the life characteristics and failure rules of products, and calculate the reliability indicators such as product failure rate and average life. The product life test can be divided into long-term life test and accelerated life test 。 (3) Special test
Special test is to test and check the relay with special instrument. This kind of test is not only used in reliability test, but also in reliability screening test. Such as X-ray inspection, infrared inspection, helium mass spectrometer leak detection, radioactive tracer leak detection, etc.
(4) Field use test
The environmental conditions for field test are the actual conditions for product use. The samples can be more and the time can be longer during the field test. Through this test, practical statistical data can be obtained, which provides a more accurate basis for improving and improving product quality. [3]
The reliability test shall be carried out according to the test location, purpose, project, product development stage stress It can be divided into several types according to the strength of, the destruction of the test object, and the different sampling plans. For example: 1. According to the test location, it can be divided into laboratory test and field test;
2. According to the test items, it can be divided into environmental test, screening test and life test;
3. According to the test purpose, it can be divided into reliability measurement test, reliability verification test and Reliability growth test ； 4. According to the product development stage, it can be divided into development test, identification test and acceptance test;
5. According to the strength of applied stress, it can be divided into normal stress test and enhanced stress test;
6. It can be divided into destructive test and non-destructive test according to whether the test object is damaged or not;
7. According to the sample size, it can be divided into full test and sampling test;
8. According to the sampling plan, it can be divided into fixed time censoring test, fixed number censoring test and sequential test. [4]
The reliability test can generally be carried out according to the following procedures.
(1) Determine the test type according to the test purpose and product conditions;
(2) Assumed product life distribution type;
(3) Select the test scheme according to the product batch and cost;
(4) Determine the upper and lower limits of product reliability indicators according to technical and economic conditions;
(5) Formulate a sampling plan according to the test plan and given parameters to determine the number of test objects and test time;
(6) Determine the test conditions, including environmental conditions, working conditions, load conditions and the initial state of the test object;
(7) Specify the parameters to be measured and the corresponding measurement methods and periods according to the product performance;
(8) Formulate criteria for fault classification and judgment;
(9) Specify the items, contents and corresponding formats to be recorded;
(10) Carry out data analysis and processing, judge test results and put forward test reports. [4]
Due to economic and time reasons, it is usually not to conduct reliability tests on all products, but to take an appropriate number of samples from a batch of products for tests according to certain principles and procedures, and use the results of these sample tests to judge whether the reliability level of the batch of products meets the requirements of the standard or the order contract, Or to estimate the value of the reliability characteristic quantity of the batch of products. These samples are called sub samples or samples, and the batch of products from which samples are taken is called parent, population or batch. It is possible to judge some products with high qualification rate as unqualified or some products with low qualification rate as qualified by sample test. The former is called producer risk, that is, the probability of rejection when the actual reliability level of the product is equal to the acceptable reliability level, expressed in α; The latter is called user risk, that is, the probability of acceptance when the actual reliability level of the product is equal to the ultimate reliability level, expressed in β. The sampling plan is a way to calculate the sample number n from a batch of products N according to the upper and lower limits, α and β values of the given reliability index under the premise of a certain risk. [4]
