Accelerated Life Testing...Why?
Today's market is fast and furious and timing is everything. What may have taken years to accomplish in the past can now be done in months, or even weeks. If you can release a reliable product before your competitors can release theirs, then you have gained a great advantage. But how can you gain this advantage in time to market? One factor that can play an important role is accelerated life testing.
Accelerated life testing is still a relatively new subject in reliability engineering, but it is starting to gain greater acceptance in the industry. Accelerated life testing is the process by which a product is forced to fail more quickly than it would have under normal use conditions. Forcing the product to fail more quickly reduces test time and still allows you to understand the life characteristics of the product. Conceptually, this is a wonderful idea, but there are still many concerns. How do I set up an accelerated life test? What are the benefits? How much will it cost and how much time/money will it save me? The answers to these questions are not simple and straightforward, but when is anything worth having easily accomplished?
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 estimation of the probability of failure of the product under use conditions, mean life under use conditions, projected returns and warranty costs. It can also be used to assist in the performance of risk assessments, design comparisons, etc.
So, which type of accelerated test should you conduct? Well, it depends. Both types of accelerated tests will allow you to collect information to increase the reliability of the product. But if you actually would like to be able to quantify what the reliability is, then you would conduct a quantitative test. In reality, you would probably conduct both types of tests and you can use the information gained from the qualitative test to help in setting up the quantitative test.
an Accelerated Life Test
Figure 1: Typical stress range for a component, product or system.
The choice of stresses and stress levels, along with the process of setting up the experiment, is of the utmost importance. Consult your design engineer(s) and material scientist(s) to determine what stimuli (stress) is appropriate, as well as to identify the appropriate limits (or stress levels). If these stresses or limits are unknown, multiple tests with small sample sizes can be performed in order to ascertain the appropriate stress(es) and stress levels. Proper use of Design of Experiments (DOE) methodology is also crucial at this step. In addition to proper stress selection, the application of the stresses must be accomplished in some logical, controlled and quantifiable fashion. You must maintain accurate data on the stresses applied as well as the observed behavior of the test specimens. Bottom line...you must do your homework upfront before conducting an accelerated life test. Any error that exists in any guess will most certainly be discovered later, which in general, usually means you go back to square one. Spending the time and money ahead of time is definitely an investment, but it is an investment that you cannot afford not to take.
The actual acceleration factor that you can expect from an accelerated life test will depend on the characteristics of the product being tested. If you are expecting acceleration factors on the order of 100s or even 1000s, then unfortunately you will be disappointed. It is possible to design a test with an acceleration factor of, say, 500, but the test is not likely to yield useful information.
When properly applied, accelerated life testing can provide valuable information and in today's market, the sooner that information can be gathered the better off you will be. And once you have the information, analyzing the data has become much easier using ReliaSoft's ALTA software. Accelerated life testing is simply one of the available methods that you can use to learn about your product more quickly. Once you have gathered the information, you can make knowledgeable decisions about how to proceed.
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