failure modes

huangyhg

failure modes?
there is this contractor who is substituting a standard arm of an excavator to a much longer arm
(lengthened about 50%). he is using this excavator to drive down some steel c sections (size about 150-200 mm) into ground (these piles are like temporary supports for main excavation). he says that the operating condition is that the boom is only acting like a link to obtain deeper reach, and driving mechanism is attached in place of the bucket.
my question is that what can be possible failure modes of the excavator boom other than buckling? is there a need for a detailed fea analysis to ensure the structural adequacy of the boom?
have any one of you ever experienced failure of an excavator boom??
one possible failure mode is bending.  another is overturning of the machine.  another is overloading something else back behind the section in question.
i would not see this as something requiring fea.
if it's a link with pin joints at each end then you won't have bending. i'd do a static analysis on the loads to calculate the forces in each   
longer arms are common for slurry wall trenching.  only  other change is new arm may have dual cylinders.   
whats the reason for worrying? isnt this a means and methods for the contractor to worry about? also, whats the weight of the driving end? compare that to the regular arm bucket capacity and derive a overturning moment. i would defer this the the mfg too
thank you for the posts everyone..
we are worrying as we r responsible for submitting calcultions for this modification work and certify so tht the owner is worryfree
jrisebo,
perhaps the op is an engineer working for the excavator manufacturer.