Hello all,
I am from the University of Missouri's FSAE team and am working on the suspension for this year. I'm at a roadblock on trying to size the a arms.
I have already calculated the expected tire forces, and used our suspension geometry to do a 'truss analysis' of the system. From here we can see the expected tensile and compressive loads for all of our different cases (accel, cornering, braking, bump, and combined cases). From here I did some basic buckling calculations using the Euler formula to find the critical load. The consensus here was that we can run 1/2" 0.035 tubes for pretty much everything and we would have plenty of room for safety. However, the euler formula assumes perfectly concentric loading, which is never going to be true. We can estimate some error for manufacturing tolerances and calculate the eccentric loading case, and this still gives us a plenty of room for safety under realistic manufacturing tolerances.
I know from past experience that realistically if all of our a-arms were this small (1/2 inch 0.035) they would likely deflect a lot and possibly break. It seems that the error comes from the fact that our suspension links are not all 2 force members like we assume when we did our load calculations. The fact that the ends are welded together at the outboard spherical means they can exert a moment, and introduce bending into the situation. This is where I am stuck - I don't think it is possible to look at it like a basic statics problem if you make them "welded" joints. Short of running extensive FEA using our load cases on each corner, are there any calculations that can be done in order to estimate the amount of eccentric loading/bending that will be put into the arms? It seems that this will be of greater magnitude than any perfect tension/compression forces that we can calculate using basic static analysis.
Hate to be that guy that just posts to ask everyone to do the work for him - but I'm just curious if there is anything that can be done here short of "just overbuild them and test the car" or doing all the FEA, which it seems we are going to have to do. If you'd like to see specifics on what I have done so far I'd be happy to share.