IEC 62506-2013 pdf free download.Methods for product accelerated testing.
4 General description of the accelerated test methods
4.1 Cumulative damage model
Accelerated testing of any type is based on the cumulative damage principle. The stresses of the product in its life cause progressive damage that accumulates throughout the product life.
This damage may or may not result in a product’s failure in the field.
The strategy of any type of accelerated testing is to produce, by increasing stress levels during testing, cumulative damage equivalent to that expected in the product’s life for the type of expected stress. Determination of product destruct limits， without reliability estimation, provides information on whether there exists a sufficient margin between those destruct limits and product specification limits, thus providing assurance that the product will survive its predetermined life period without failure related to that specific stress type. This technique may or may not necessarily quantify a probability of product survival for its life, just assurance that the necessary adjustments in product strength would help eliminate such failure in product use. Where sufficient margins are determined unrelated to the probability of survival, the type of test is qualitative. In tests where this probability of survival is determined, the magnitude of the stress is correlated to the probability that the product would survive that stress type beyond the predetermined life, and this test type is quantitative.
Figure 1 depicts the principle of cumulative damage in both qualitative and quantitative accelerated tests.
In Figure 1, for simplicity, all stresses, operating limits, destruct limits, etc. are shown as absolute values. The specification values for an item are usually given in both extremes, upper and lower, thus the upper and lower (or low) specification limit, USL and LSL with the corresponding design limits (DSL), UDL and LDL, the upper and lower operating limits, UOL and LOL, and also the reliability test limits, URTL and LRTL. The rationale is that the opposite (negative stresses, may also cause cumulative damage probably with a differently failure mechanism, thus the relationship between the expected and specified limits can be ilustrated in the same manner as for the high or positive stress. As an example, cold temperature extremes might produce the same or different failure modes in a product. To avoid clutter, the positive and the negative thermal or any other stresses are not separately shown in Figure 1, thus the magnitudes of stresses are either positive or negative, and thus represented as absolute values only as upper or lower limits.IEC 62506 pdf download.