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1. Introduction
At present, each company's corporate standards contain a certain number of test items, which are often a series of tests consisting of one or more groups of different test items. This kind of test in which the test sample is exposed to two or more environments in sequence is called a combination test. Rather than a comprehensive environmental test like a typical reliability qualification test. Different types of tests have different purposes.
If you want the test to achieve the predetermined goals, you should consider the completeness of the test items, the rationality of the test conditions, the scientific nature of the test items and test sequences, as well as the test methods and specific tests used.
Four factors of program reproducibility. It should be pointed out that in the past test standards and test practices, people paid more attention and attention to the selection and determination of test items, test conditions, test procedures and the selection of test methods, and paid less attention to the interaction and interaction between each test item. Sequence arrangement.
Many products are only considered to complete the test items specified in the technical conditions. The sequence of the test items often depends on the condition of the test samples, the progress of the development and production plan, the time conditions of the test equipment and test personnel. This practice of arbitrarily determining the order of implementation of the test projects without considering the interaction between the environmental test projects actually seriously affects the credibility and comparability of the test results.
This article focuses on the related technologies of arranging the sequence of pilot projects. Suggestions on the sequence arrangement of each test. By comparing some external standards and analyzing the failure mechanism of each test item, a recommended order of enterprise standard reliability tests is proposed for reference by development engineers.
In addition, the acceptable standards for product performance and structural integrity should be clearly stated in the relevant specifications before testing. Some simple examples include:
Description of performance maintenance;
Achievement of all or specified parts of technical performance;
Allowable degree of performance degradation;
Results of visual inspection of the product.
2. Sequence of test items
As mentioned above, testing is often a combination of tests.
This combination test mainly consists of a series of single-factor test items that simulate a single influence, which also includes some comprehensive test items such as temperature-vibration test. When designing an environmental test program, you will inevitably encounter three problems:
first, how to group test samples;
second, when using the same test sample to conduct multiple test projects, the order should be arranged randomly or according to certain principles; third Is there a requirement for the time interval between the two test items, and whether the testing before and after the test can be simplified. Among these three problems, the first one is easily taken seriously. This is because some test items or a certain test procedure in the test items are destructive, such as durability test and salt spray test. Since these tests cannot be performed at the same time, It is arranged at the end of the test sequence, and usually more than two groups of samples are arranged for testing.
For the purpose of saving test sample funds, various measures should generally be taken to reduce the number of groups as much as possible. For example, based on the characteristics of salt spray test and mold test and evaluation, which are generally irrelevant to product functions, they are arranged last and conducted on test pieces with damaged functions.
The second issue regarding the order of test items is more complex, and the impact of the previous test on the subsequent test needs to be considered. Since the assessment of different test items has different impact mechanisms on the test samples, different test sequence arrangements will inevitably lead to different test results.
Therefore, when one or a group of samples are used to conduct multiple environmental test items in sequence, the possible interactions between each test item should be carefully studied, and the optimal sequence of test items should be tailored and designed according to the purpose of the test to ensure that the combined test Consistency and comparability of results.
The third question is relatively simple, because usually the interval between each single-factor test item will not have a significant impact on the test results, so there is no clear regulation on this time, but it should generally be done before and after each test item.
Carry out initial testing and final testing to ensure that qualified products are put into this test and evaluate the results or impact of the test.
Normally, samples should be pre-treated, restored and stabilized between each test. BOTO recommends that when two adjacent test projects are separated by a short period of time and the tests are conducted in the same laboratory with little change in indoor environmental conditions, the final test of the former test can be used as the basis for the latter test. Initial detection to simplify testing.
3. Principles for considering the order of test projects
Generally speaking, in addition to the response characteristic investigation test, no matter what type of test is performed at which stage of development and production, as long as two or more test items are conducted consecutively, the sequence arrangement of the test items must be considered. However, for different Due to different test purposes, the principles for arranging the sequence of test items are often different for different types of tests.
3.1 Adaptability development test The adaptability development test is mainly used to discover design defects and weak links of the product under test, to provide information for improving product design, and of course to verify design correction measures. The order of test items in this test generally follows the following principles:
1) If the purpose of the test is to obtain information on product reliability design defects in the shortest possible time in order to improve the design as soon as possible, and the number of test samples available is limited, it is often necessary to start with the most severe test items, or to test the test samples Start the test items with the greatest impact so that defects in the test samples are exposed as quickly as possible and the entire test is terminated quickly.
2) If the purpose of the test is to obtain as much performance data as possible before the test sample is damaged (especially when the number of test samples is small), start with the test that has the least impact on the performance of the test sample (i.e. non-destructive test) , so that as many test items as possible can be done before the test sample is damaged.
3.2 Qualification test and acceptance, routine test design The purpose of qualification test and batch production product acceptance and routine test is to check whether the reliability of the tested product meets the requirements stipulated in the technical conditions, and to provide guidance for the design and finalization of the developed product and the quality of the batch production product.
Acceptance provides the basis for decision-making and is a test for compliance inspection. The results of this test evaluation have a significant impact on the work progress and interests of both the developer, manufacturer and user.
Therefore, it is a test that must be strictly controlled. Particular attention must be paid to the reproducibility, comparability and correctness of the test results. In addition, this kind of test often involves many test items.
For example, the qualification test often requires all test items specified by the technical conditions. Therefore, it is particularly important to correctly tailor the sequence of test items. Generally, the sequence of test items is designed according to the following two principles:
1) When the use environment of the test sample can be predicted, the test sequence should be consistent with the order in which the environmental conditions experienced by the product during production, transportation, storage and use are as consistent as possible. This is the most ideal sequence for product assessment.
2) When the use environment of the test sample is unpredictable, the order that has the most severe impact on the product is often adopted.
At this time, it is necessary to consider the problem that the results produced by the previous test can be exposed or strengthened by the later test.
To choose a good test sequence, you must first understand and master the impact of various single environmental factors on the test sample and the possible failures;
secondly, you must understand the impact of different initial states of the test sample on the test;
thirdly, you must master the different test sequences. The similarities and differences between the failure situation of the test sample and the actual failure situation under the conditions, and strive to find the test sequence that best matches the actual situation.