And again there is no one answer for such simple question. Strongly depends on what type of test you need to conduct.
It is also very important to understand at which stage, design of the product. Usually at very early stages of the design there is many unexpected failures, when design is mature enough – failures become predictable, and there is one last period, called – wear out/aging stage.
To visualize it, there is famous Bathtub curve:
Y axis – is failure rate and X axis is Time, can be cycles, hours, years etc.…
Every design follow this pattern (the only exclusion is Software Development, but this is separate topic), even we, as a human been, following same pattern:
As a product developer, you probably want release your product after “Early Failure period” stage. And now, you need test it, to show that the product is capable to serve some period of life. In one of my previous articles, I have touch base regarding the sample size.
In general there is 3 major durability type of tests:
Bogey test – durability test, usually based on previous historical test and used as a benchmark test. Very often without relation to real duty cycle of the product.
Run to failure(RTF) – durability, usually used to identify different type of failures per different type of loads. Usually driven by FMEA, and based on those results can be defined the life of product based on distribution.
Degradation test – this durability test usually reflect aging and wear out life of the product. During this test should be identifying time intervals to measure the degradation level of the product. This is test can predict full life of the product.
In general before doing any test, one should ask himself, what type of failures this test should discover? How the test conditions related to the real duty cycle of the product?
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