Assessing Product Reliability
8.1.5. What are some common acceleration models?
|The Eyring model has a theoretical basis in chemistry and quantum mechanics and can be used to model acceleration when many stresses are involved||Henry Eyring's contributions
to chemical reaction rate theory have led to a very general and powerful
model for acceleration known as the Eyring Model. This model has several
for which S1 could be some function of voltage or current or any other relevant stress and the parameters , H, B, and C determine acceleration between stress combinations. As with the Arrhenius Model, k is Boltzmann's constant and temperature is in degrees Kelvin.
If we want to add an additional non-thermal stress term, the model becomes
and as many stresses as are relevant can be included by adding similar terms.
|Models with multiple stresses generally have no interaction terms - which means you can multiply acceleration factors due to different stresses||Note that the general Eyring model includes
terms that have stress and temperature interactions (in other words, the
effect of changing temperature varies, depending on the levels of other
stresses). Most models in actual use do not include any interaction terms,
so that the relative change in acceleration factors when only one stress
changes does not depend on the level of the other stresses.
In models with no interaction, you can compute acceleration factors for each stress and multiply them together. This would not be true if the physical mechanism required interaction terms - but, at least to first approximations, it seems to work for most examples in the literature.
|The Eyring model can also be used to model rate of degradation leading to failure as a function of stress||Advantages of the Eyring Model
|In practice, the Eyring Model is usually too complicated to use in its most general form and must be "customized" or simplified for any particular failure mechanism||Disadvantages of the Eyring Model