|Quoting amccann (Thread starter):|
My curiosity stems from a recent flight on an ERJ145. While boarding I noticed a main entry door corner doubler repair, typically an indicator of fatigue damage.
|Quoting tdscanuck (Reply 1):|
As a result, it's expected to develop fatigue cracks prior to its design service life. The entire point of damage tolerant designs is to assume that undetectable cracks are present at day one and then inspect for and catch them before they reach critical length. If a modern jet reaches it's design service life without any cracks then it was either incredibly lucky or grossly over-designed.
|Quoting amccann (Reply 2):|
It seems logical with the increasing regional jet cycles and damage tolerance principles that doubler repairs would/will be more common as regional jet cycles continue to increase.
|Quoting Starlionblue (Reply 3):|
Sure. However remember that airliners are designed and built for the expected type of operation. For RJs, you're talking multiple daily cycles. For a 777, you're talking one daily cycle. So it doesn't follow that RJs necessarily fall apart earlier if you compare cycle for cycle.
|Quoting amccann (Reply 4):|
It is reasonable to state that a properly designed long haul product at X number of cycles will have the same probability of cracking as a properly designed short haul product at X number of cycles if their Service Life is similar.
|Quoting amccann (Reply 4):|
However a basic SN curve will demonstrate the "primary" driver of fatigue is cyclical loading.
|Quoting m1m2 (Reply 7):|
|Quoting tdscanuck (Reply 5):|
The *stress* is hugely important (that's why it's usually log-log). An aircraft designed for a lot of cycles will tend to run at lower stress so that the cracks don't grow as fast.
|Quoting Roseflyer (Reply 6):|
The CRJ is designed for 60,000 cycles. I haven't seen the embraer MPD to see their numbers. See below for most airplanes.
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