Nearly all and everything contemporary produced is completely designed within a
digital computer specified environment; from electronics to mechanical; covering
design criteria such as Thermal Expansion & Conductivity, Modal Frequency
Vibrational Response, Dynamic Physical Loads & Gravity, Material Elasticity
Stress
& Strain, Chemical Interactions... This is a very basic matrix of R&D analysis.
When a company such as Bombardier develop a power train it is run through the
above
matrix before being produced and released for industry use.
The factory supplied 9XX exhaust system will have the above matrix applied along
with field testing results which are fed back into the design process upon a
"Continual Improvement" basis, which the end user sees as optional or mandatory
factory Service Bulletins.
This closed loop system quickly falls apart when third party aftermarket
components
are brought into the mix; some may cause premature failure, others may prevent
it; it depends upon the applied knowledge of who ever is producing the
component.
The whole exhaust is constantly vibrating at (x)hz at (x)deg and will be tested
at the factory based upon the typical operating ranges of the power unit being
in the vicinity of 5100rpm and (x)deg give or take 15% either side. Stress and
strain fatigue points of the exhaust system will naturally be found around
both bending points, and attachment points. Hard mounting the exhaust muffler
to the engine block moves any inertia forces of the exhaust into the engine
block
which may or may not be designed to support such loads beyond (x)hrs of usage
at (x)rpm.
A rough running engine or loose fixing somewhere in the mix adds another
dimension
of vibration into the fatigue failure equation.
This why its important to keep any motor well serviced and tuned and running
smooth.
The short answer to the question is "Cycle Count" but that is just going to be
too cryptic for most to understand.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510499#510499
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