Functional test parameters with degradation measures may be required to obtain meaningful test results of long lived products. Difficulty in handling the stress combination combined with the possibility of non-linear behavior may result in changes to an accelerated test. Add intermittent or soft system failures to this mix and reliability challenges increase. Data analysis of a small number i. Sample size selection should represent as wide a variability as possible.
Often available samples is smaller than desired and this complicates test planning and results. Degradation measures become indispensable when zero failures occur in test. Data collection times during test may also impact the analysis especially when looking for non-linear behavior. Test data collection points are set for convenience of reading and not to yield the best spread of information for analysis.
Abstract Three laboratory-based accelerated corrosion tests were investigated to develop improved procedures for assessing corrosion protection properties of organic paint films. The methods … Expand. Environmental and electrochemical test methods for the evaluation of protective organic coatings. Evaluation des proprietes anticorrosives de revetements organiques a l'aide de trois essais d'exposition acceleres et de deux essais electrochimiques.
Related Papers. Normally, these stress levels will fall outside the product specification limits but inside the design limits. Stress Types and Stress Levels In an effective overstress acceleration life test, the analyst chooses one or more stress types that cause the product to fail under normal use conditions. This can include temperature, voltage, humidity, vibration or any other stress type that directly affects the life of the product under normal use conditions.
The stress es are then applied at various accelerated levels and the times-to-failure and times-to-suspension for the units under accelerated test conditions are measured.
For example, if a product normally operates at Kelvin and high temperatures cause the product to fail more quickly, then the accelerated life test for the product may involve testing the product at K, K and K in order to stimulate the units under test to fail more quickly.
In this example, the stress type is temperature and the accelerated stress levels are K, K and K. The use stress level is K. When the stress is constant, the stress level applied to a sample of units does not vary with time. Each unit is tested under the same accelerated temperature for the duration of the test.
For example, ten units are tested at K for hours, ten different units are tested at K for hours and ten different units are tested at K for hours.
When the stress is time-dependent, the stress applied to a sample of units varies with time. Time-dependent stresses can be applied in a variety of ways. For example, if temperature is the stress type, each unit may be tested at K for 10 hours then increased to K for 10 hours then increased to K for 10 hours over the duration of the test.
Alternatively, the units may be placed in a test chamber where the temperature starts at K and increases by five degrees every ten minutes until the chamber reaches K. Some common types of time-dependent stress profiles include step-stress, ramp-stress and various profiles in which the application of the stress is a continuous function of time. Figure 1 and Figure 2 display two examples of the many time-dependent stress profiles that can be used in an accelerated life test design.
Weibull, exponential or lognormal that best fits the data at each stress level. This results in an overstress probability density function pdf for each accelerated stress level. Another mathematical model, the life-stress relationship, is then required to estimate the probability density function pdf at the normal use stress level based on the characteristics of the pdf s at each accelerated stress level. The plot in Figure 3 demonstrates the relationship between life and stress for a particular product.
Figure 3: Graphical demonstration of the relationship between life and stress When analyzing accelerated life data, the analyst must select a life-stress relationship that fits the data for the particular product.
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