Each type of test that has been called an accelerated test provides different information about the product and its failure mechanisms. These tests can be divided into two types: qualitative tests (HALT, HAST, torture tests, shake and bake tests, etc.) and quantitative accelerated life tests. This reference addresses and quantifies the models and procedures associated with quantitative accelerated life tests.
Qualitative Accelerated Life Testing
Qualitative tests are tests that yield failure information (or failure modes) only. They have been referred to by many names including:
?/FONT> elephant tests
?/FONT> torture tests
?/FONT> HALT tests
?/FONT> shake and bake tests
Qualitative tests are performed on small samples with the specimens subjected to a single severe level of stress, to a number of stresses or to a time-varying stress (i.e. stress cycling, cold to hot, etc.). If the specimen survives, it passes the test. Otherwise, appropriate actions will be taken to improve the product's design in order to eliminate the cause(s) of failure.
Qualitative tests are used primarily to reveal probable failure modes. However, if not designed properly, they may cause the product to fail due to modes that would have never been encountered in real life. A good qualitative test is one that quickly reveals those failure modes that will occur during the life of the product under normal use conditions. In general, qualitative tests are not designed to yield life data that can be used in subsequent quantitative accelerated life data analysis as described in this reference. In general, qualitative tests do not quantify the life (or reliability) characteristics of the product under normal use conditions, however, they provide valuable information as to the types and level of stresses one may wish to employ during a subsequent quantitative test.
Benefits and Drawbacks of Qualitative Tests
?/FONT> Benefit: Increase reliability by revealing probable failure modes.
?/FONT> Provide valuable feedbackin designing quantitative tests and in may cases they are a precursor to a quantitative test.
?/FONT> Unanswered question: What is the reliability of the product at normal use conditions?
Quantitative Accelerated Life Testing
Quantitative accelerated life testing (QALT) unlike the qualitative testing methods described previously, consists of tests designed to quantify the life characteristics of the product, component or system under normal use conditions and thereby provide reliability information. Reliability information can include the determination of the probability of failure of the product under use conditions, mean life under use conditions and projected returns and warranty costs. It can also be used to assist in the performance of risk assessments, design comparisons, etc.
Quantitative accelerated life testing can take the form of usage rate acceleration or overstress acceleration. Both accelerated life test methods are described next. Because usage rate acceleration test data can be analyzed with typical life data analysis methods, the overstress acceleration method is the testing method relevant to both ALTA and the remainder of this reference.
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可是还没有看到一半，看不下去了。
只知道他认识我，我不认识他了。。