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1、1. WhatAsccelerated Life Testing(1) What is Accelerated Life Testing?Traditional life data analysis involves analyzing times-to-failure data (of a product, system or component) obtained under normal operating conditions in order to quantify the life characteristics of the product, system or componen
2、t. In many situations, and for many reasons, such life data (or times-to-failure data) is very difficult, if not impossible, to obtain. The reasons for this difficulty can include the long life times of todays products, the small time period between design and release and the challenge of testing pr
3、oducts that are used continuously under normal conditions. Given this difficulty, and the need to observe failures of products to better understand their failure modes and their life characteristics, reliability practitioners have attempted to devise methods to force these products to fail more quic
4、kly than they would under normal use conditions. In other words, they have attempted to accelerate their failures. Over the years, the term accelerated life testing has been used to describe all such practices.A variety of methods that serve different purposes have been termed accelerated life testi
5、ng. As we use the term in this reference, accelerated life testing involves acceleration of failures with the single purpose of quantification of the life characteristics of the product at normal use conditions.More specifically, accelerated life testing can be divided into two areas: qualitative ac
6、celerated testing and quantitative accelerated life testing. In qualitative accelerated testing, the engineer is mostly interested in identifying failures and failure modes without attempting to make any predictions as to the products life under normal use condInitqiuoannst.itative accelerated life
7、testing, the engineer is interested in predicting the life of the product (or, more specifically, life characteristics such as MTTF, B(10) life, etc.) at normal use conditions, from data obtained in an accelerated life test.(2) Types of Accelerated TestsEach type of test that has been called an acce
8、lerated 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 a
9、nd procedures associated with quantitative accelerated life tests.Qualitative Accelerated Life TestingQualitative tests are tests that yield failure information (or failure modes) only. They have been referred to by many names including: elephant tests torture tests HALT tests shake and bake testsQu
10、alitative 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
11、improve the products 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
12、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
13、. 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 o
14、f Qualitative Tests Benefit: Increase reliability by revealing probable failure modes. Provide valuable feedbackin designing quantitative tests and in may cases they are a precursor to a quantitative test. Unanswered question: What is the reliability of the product at normal use conditions?Quantitat
15、ive Accelerated Life TestingQuantitative 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 inform
16、ation. 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 ove rstress acceleration. Both accelerated life test methods are
