In today’s highly competitive market environment and the background of globalization, in order to quickly and successfully occupy the domestic and foreign markets, products must not only meet the performance requirements, but also improve the environmental adaptability and reliability of products. Therefore, environmental test and reliability test comply with the needs of the market and are valued by all walks of life at home and abroad. This paper focuses on the relationship between environmental test and reliability test.
1.Concept and research contents
Environmental test is an important part of environmental engineering, which plays an important role in the development, production, storage and use of products. It is an important means to ensure the environmental adaptability of products.
Environmental test is the process of applying certain environmental conditions to products according to certain methods and procedures to test the environmental adaptability of products. The environmental conditions include natural environment, use environment and laboratory environment. It can be divided into the following categories according to the attributes of environmental factors:
1) Climatic factors, including temperature, humidity, air pressure, rain, snow, ice, frost, sand and dust, salt fog, corrosive gases, etc
2) Mechanical factors, including vibration, impact, swing, constant acceleration, explosion, earthquake and noise vibration
3) Biological factors, including molds, insects, marine organisms, etc
4) Electromagnetic radiation factors, including radio interference, lightning, electric field and magnetic field, etc., certainly include the new environment after the combination of these environments.
Environmental test can be divided into environmental adaptability development test, environmental identification test, environmental acceptance test and environmental routine test according to its role and task in different stages. Reliability test also runs through all stages of product research and production to verify whether the product has the original function after a period of time.
2.Environmental test and Reliability test
At present, the international authoritative standards in the field of environmental test and reliability test are MIL-STD-810F Environmental Test Methods and Engineering Guidelines and MIL-STD-781D Reliability Test for Engineering Development, Qualification and Production. In a sense, any test can be regarded as an environmental test, because the test is always conducted in a certain environment. Therefore, reliability test can also be regarded as an environmental test. Environmental tests are also included in strength, life, performance tests and other basic tests.
Usually, people only refer to some specific test stages in the product development process as environmental tests. From the perspective of reliability, environmental tests and any other tests are intended to improve or assess the performance of products. The conduct of these tests is conducive to the improvement of product reliability. MIL-STD-781D clearly points out that these tests can be considered as part of reliability tests. MIL-STD-785B System and Equipment Development and Production Reliability Program also points out that “The environmental tests described in 810F should be regarded as an early part of reliability development and growth. These tests must be carried out at the early stage of development to ensure that there is enough time and resources to correct the defects exposed in the tests, and these corrective measures must be verified under environmental stress, and these information must be included in the FRACAS system as an indispensable part of the reliability outline”.
It can be seen from the provisions on the test purposes of environmental test and reliability test that they are both aimed at exposing the defects in product design, materials, components and processes. Comparing their test items, we can find that. In MIL-STD-810F, extreme value conditions are adopted for environmental stress values, while in MIL-STD-781D, strict simulation of actual use environment is required, and typical environmental conditions are adopted. In addition, there are differences between the two in the amount of environmental stress used in the test, test type, test time, and test termination criteria. In a broad sense, environmental test and any other test are to improve or assess the performance of products, which is conducive to the improvement of product reliability. It can be seen that environmental test is closely related to reliability test. The former is the basis of the latter, which plays an important role in improving product reliability.
2.1 Relationship between environmental test and reliability test
The environmental test is a series of tests for the purpose of finding environmental design defects of products, verifying the adaptability of products to extreme environments during their life cycle, and investigating the response characteristics of products to environmental effects. For products that have passed the function test at room temperature, various environmental tests shall be carried out first to ensure that the products will not be damaged and can work normally in various extreme environments in the future life cycle. Therefore, the environmental test is more basic than the reliability test. It is carried out before the reliability test at all stages of product development and production.
Environmental test is the most basic test of products. Only products passing the environmental qualification test can be put into reliability growth test; products passing the environmental acceptance test can be put into reliability acceptance test. Therefore, it can be said that environmental test is the basis and precondition of reliability test. Reliability test just makes use of the research results of environmental test on environmental conditions. Poor product reliability is often caused by poor use of environmental conditions. For example, high temperature will cause thermal aging, leading to failure of insulation, low temperature will cause the reduction of part volume, causing structural damage, sand and dust, causing blockage, moisture causing electrical corrosion, and vibration impact causing stress corrosion.
In order to ensure that the product can complete the specified functions under the use environment conditions and reach the quantitative reliability index value required by the contract, it is necessary to first understand the future use environment conditions of the product and carry out the product reliability design according to this requirement. All types of reliability design and prediction must be combined with appropriate environmental stress. In terms of improving product reliability, environmental testing plays an important role. To be extreme, without environmental testing, it is impossible to correctly identify product quality and ensure product quality. The more authentic the environmental test, the better the reliability of the product. The type and quantity of environmental stress must refer to the research results of environmental testing.
At the same time, these two kinds of tests basically adopt laboratory test methods and are conducted in the specified controlled environment. The environmental equipment and test methods used, including the corresponding fixture design principles, can be used for reference. The study of environmental conditions used for environmental tests provides prerequisite information for the establishment of reliability test conditions. At the same time, the determination of temperature and vibration values in the reliability test profile is basically the same as the determination of corresponding environmental conditions. It can be considered that environmental test is the basis and premise of reliability test, and many environmental tests should be carried out before reliability test to provide information and basis for reliability test.