By J. M. Pimbley
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Additional info for Advanced CMOS process technology
Unfortunately, once an accelerated test has been in use for several years the theory behind it becomes obscured and the successes with evolved designs become the justification of the method. Where there are radical design alterations results can be totally misleading. (c) Laboratory tests The methods described so far have relied on the component operating in the whole vehicle structure to supply the correct loading input. This approach is good for vehicle manufacturers who need to prove and test complete vehicles.
Until recently engineers have been forced to make estimates with very little information other than experience of their own and other people's failures. Many are still doing so. These estimates are usually concerned solely with the maximum stresses the component will experience, ignoring the number of occurrences of this maximum stress and the potential fatigue damage from the many ranges of the lower stress levels. For safe design, this lack of information on the service stresses has necessitated the infinite life approach, although even here the absence of direct measurements has caused frequent failures.
It was decided therefore that the test would have to be accelerated. 11 Structural temperature in accelerated test cycle and typical Concorde flight The method used to accelerate the Concorde full-scale fatigue test was to increase the temperature of the thermal cycle, so as to increase the amount of creep and overaging and give higher thermal stresses. The effect of this was to make each test cycle represent approximately two flights. In addition, forced heating and cooling of the external and appropriate parts of the internal structure was used to speed the rates of heating and cooling.