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Originally Posted by mylesdw
Surely the nature of fatigue failure is that the part can appear 'just like new' right up until the point that it fails.
I guess that some things like this may look wrong 'on paper' but in practice the failure never occurs; The proof of the pudding is in the eating and >50K is a pretty good practical test.
On the subject of 'that' front suspension: why did you go for rocker arms and inboard springs? I always thought that was for aerodynamic reasons on open wheeled cars. Just interested.
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You are correct that the nature of fatigue failure is that the failure point often looks normal until it fails.
As you know, metal fatigue is caused by repeated cycling of of the load. It is a progressive localized damage due to fluctuating stresses and strains on the material. Metal fatigue cracks initiate and propagate in regions where the strain is most severe.
The process of fatigue consists of three stages:
1. Initial crack initiation
2. Progressive crack growth across the part
3. Final sudden fracture of the remaining cross section
I have had a number of the rod ends magnafluxed at varying points in their life and have yet to find any stress cracks in the units.
Even after some fair shunts that left the rod ends bent, there has been no cracking. However, I do stress that these joints as well as all rod ends on the chassis should be inspected between each session for damage or wear.
As to your second query.
1. Packaging. Look at all of bits and see how everything is centrally located and quite compact. Think polar moment. The new cars have pull rod rear suspension for the same reason.
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2. Motion ratios. Over-square to produce high damper shaft movement.
3. Aero. When a splitter is fitted, air needs to flow through the wheel well as cleanly as possible to insure accelerated flow on the underside of the splitter. This was also a consideration, but it is really much like gilding the lily.