Hi Peter,
Unless a helpful engineer pops up on the list, this could be quite an expensive
exercise.
Unfortunately I doubt that the TAC would accept you learning FEA and doing your
own analysis, although don't totally exclude this option. The analysis is easy
enough to learn, it's the correct application of it that requires skill.
The probable reason they are concerned about this is that Ali behaves quite
differently to steel under cyclic stress. Steel reaches a stress plateau called
the endurance limit under cyclic loading, Ali on the other hand continues to
degrade. So if a steel item is never loaded beyond it's endurance limit it has
infinite life, Ali will fail eventually even at low loads. So the "art" of
designing Ali parts is to ensure the eventual failure is well beyond the worst
case load life cycle of the part.
A quick intro to the problem can be found here
https://en.m.wikipedia.org/wiki/Fatigue_limit
I'd suggest three approaches:
1) Contact the kit supplier & any build forums to see if anyone has already
done the analysis, this may provide the info TAC are asking for.
2) Ask the TAC if they will accept a load test to say 5G is substitution for
the FEA. Unlikely for the reasons explained above, but worth a try.
3) redesign the suspension to either shift load to the lower arm or use a
spindle that is normally loaded on the top mount. I think one of our members is
building a Countach and is using Jaguar spindles. Even a change to a steel
spindle incorrectly loaded may satisfy the TAC.
I have heard of corvette spindles on a lot of custom built cars so the FEA info
may be available through a different build, e.g. something from Factory Five as
an example.
Regards,
Robin
On 29 September 2019 at 23:52 pbettany@xxxxxxxxxxxxx wrote:
Hi
This is the wording from the TAC
“The front uprights are from a C5 Corvette which in its original
configuration has a loaded lower arm (the
spring mounts to the lower arm). In its new configuration the upper arm
is the loaded arm, meaning that
the sprung weight and all bump-loads of the vehicle are now passing
through the top ball joint and top ball
joint mounting location of the upright. As the upright is made from
alloy, and was not designed for this
loading, the TAC has agreed that there needs to be an analysis done, by
an engineer, to assess the upright
and ensure that it is fit for purpose. This should be done by way of
calculations and FEA, and should
consider all applicable aspects for example vehicle weight, wheel offset,
and should include suitable safety
factoring, for example 3G bump is commonly used by LVVTA for automotive
components.”
The Honda Accord ball joint is a Moog K9643 which is the lower ball
joint. TAC didn’t say anything about this joint so I presume it’s OK
Does anybody know who can do this test?
