Acceleration life testing conditions

To complete these results, the researchers applied accelerated temperature, humidity, and bias tests (THB) to study the time-to-failure and the associated conduction and failure mechanisms [146]. The experiments were performed using the same test vehicle and adhesive materials as in the previous work. The accelerated life test conditions were 85°C and 85% RH with three different voltages 10, 50, and 100 V. The results and observations of the authors can be... 

Thus, it is no longer acceptable for the formulator to delay this compatibility testing until later in the development programme. The key message is for the formulator to test early and ensure equivalence of the whole product throughout the development cycle. Leachables are specifically mentioned data on their identity and concentration in the product and placebo are required through the shelf life and also under accelerated stability test conditions. Information should be submitted on source, chemical composition and physical dimensions of the container closure system, together with control and routine extraction tests. Acceptance criteria are also required. 

To date, four different accelerated parameters or a combination of these parameters have been employed in accelerated life testing (1) elevated temperature, (2) reduced humidity, (3) open circuit voltage (OCV), and (4) cycling relative humidity (RH), temperature, potential, freeze/thaw, or start/stop conditions. 

Suppose that some units are snbjected to a constant stress accelerated life testing composed ofk stress levels. The testing units belong to old products with an initial period denoted Tq at nse condition, which are not perfect when they arrive at accelerated life testing. 

Differences of opinion have existed for decades with respect to the mixture of corrosive gases that should be used in test chambers. For air-conditioned electronic equipment rooms in urban environments that are well removed from industrial pollution (Class II Battelle environment, G1 IBM environment, and lEC Class II environment), the appropriate Battelle accelerated life test calls for use of 200 ppb NO2, 10 ppb H2S, and 10 ppb CI2 at an RH of 70 %. This test does an excellent job of simulating corrosion films on silver, copper, tin, and some gold-plated metals, but has been criticized in recent years because the Aims it produces on nickel are unrealistic. 

Fig. 13.16 Qualification of the moisture resistivity of two modules with different degradation processes resulting in different time-to-feilure and different activation energies for three different climatic stress conditions. The longer time to failure in accelerated life testing for the module indicated in red does not result in better durability in operation compared to the second module...

According to the above method, we can estimate the acceleration coefficient and carry out experiment design and evaluation. We should note that this method is based on the stress reliability prediction method. If the expected value cannot fully reflect the accelerated stress, the use of this method is restricted, such as multiple stress accelerated life test, etc. And for satellite unit, due to the complexity of its failure mechanism, failure rate ratio can only be as a reliability characterization of the product in different conditions but not as an accurate measure of life characteristic value, and there is no accurate theoretical basis. 

For faster product development or improvement, accelerated life testing (ALT) can be used to determine the reliability of implants in accelerated use conditions [79]. Accelerated life testing helps to identify failures and failure modes qualitatively or predicts package lifetime quantitatively at normal use conditions (Accelerated Life Testing Online Reference, ReliaSoft s eTextbook for accelerated life testing data analysis [80]). 

SIR tests are accelerated aging tests. Accelerated life tests (ALT) are used to determine the expected lifetime in the use environment. To obtain this data, a statistical number of test coupons are exposed to accelerated conditions and tested to failure. Several temperature conditions are needed to determine the activation energy for the process, as indicated in the Arrhenius equation helow ... 

Test, particularly related to the qualification or life test. In the qualification testing the adequacy of the lubrication system shall be demonstrated under a more extreme range of simulated conditions (usually thermal). In the life test the adequacy of the mechanism design, lubricant lifetime and performance shall be demonstrated under representative conditions (eg thermal, motion profile, durations, loads etc). If accelerated life testing is performed (which is normal) the conditions must be... 

A comparison between the accelerated tests and the operational life tests provides an acceleration factor . A major concern in accelerated life tests is to be sure that you are accelerating the right degradation mechanism. Most often both life tests and accelerated tests are run. In addition, control samples (shelf samples or archival samples) are kept in pristine condition so that aged samples can be compared to the original materials. This type of test has... 

Accelerated life test (adhesion) A test conducted at a stress higher than that encountered in normal operation for the purpose of producing a measurable effect such as the loss of adhesion, in a shorter time than experienced at normal operating conditions. Examples Elevated temperature concentrated chemical environment. 

The length and amount of cracks is assessed according to the Bayer method [72,73]. The ISO standard ozone test conditions involve a test temperature of 40°C zE 1°C and an ozone level of 50 5 pphm, with a test duration of 72 h. Testing is done under static [72] and/or dynamic strain [73]. These are accelerated tests and should be used for the relative comparison of compounds, rather than for the prediction of long-term service life. The method is rather complicated and demands a long duration of ozone exposure. Therefore, in some cases the rate constants of the antiozonants reaction with ozone in solution are used instead to evaluate the efficiency of different antiozonants [74]. 

Accelerated testing depends critically on selecting a parameter whose effect on service life is so well understood that long lifetimes at low values of the parameter can be predicted from shorter lifetimes at higher values. The parameter may be the prime cause of degradation, such as in a stress-rupture test where longer lifetimes at lower loads are predicted by extrapolation from short lifetimes at higher loads. It can also be a secondary parameter, such as when temperature is increased to accelerate chemical attack while the principal factor, chemical concentration, is kept constant. This is because there is more confidence in the relation between rate of reaction and temperature than in the relation of rate of reaction to concentration. It is clearly essential that extrapolation rules from the test conditions to those of service are known and have been verified, such that they can be used with confidence. 

An indirect indication of service life is obtained simply by comparison of the performance of materials under given test conditions, the one which shows the smaller change being deemed to perform better. If one material is a standard with known service performance an estimate can be made of the other material s expected performance. Particularly with accelerated tests, this can be a dangerous assumption because the differences seen under the test conditions may not be similar to the differences realised in practice. To make a direct estimate of service life it is necessary to apply some form of extrapolation technique to measured data. 

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