Re: Trailing Arm Bolts - Engineering

[tobyp@xxxx]

Hello Group - I though that I'd "weigh in" on two points that were 
brought out here. BTW - I am very happy to see some "considering" and 
"pondering" going on here ... it is important for everyone's learning 
to gather different viewpoints on specific issues.

For the first point, "brittle bolt breaking", as noted in David's 
first paragraph; This IS a concern when the bolt is "pushed to it's 
limits". Based on my previously noted calculations, we are at, or 
above, the yield limits for the current TAB. The inevitable result is 
bending to the point of yielding, fatigue damage, and ultimately, 
fracture due to fatigue cracking. I also noted that the stresses are 
at about 1/2 the limit of my bolts. You can't generate enough load in 
the system to reach the limit of 200 KSI yield strength in the Inconel 
material that I have selected. The entire rear suspension (rubber 
bushings, washers, trailing arm assembly) will fail long before my 
bolts are stressed even close to their capability.

The second point that David brings up is the retorqueing issue for 
bolts. He is absolutely correct in that, "When using bolts and nuts 
close to their yield point ...", retorqueing can result in stretching 
and yielding. This allows joint loosening, which requires that you 
continue to retorque - until the bolt fails in tension. As noted 
above, the current TAB is near it's yield stress point just from the 
installation torque. This is before any loads are applied to it from 
driving. When my bolts are torqued, the stresses are far below the 
"elastic limit" (sorry for getting technical again!), and there will 
be no permanent (called plastic) stretching of the material. The 
Inconel bolts can be torqued an infinite number of times, barring any 
damage to the threads, and never suffer from "plastic deformation". 
Okay ... I'm done for now. Thanks for your patience with me.

BTW - I have received indications of interest for 31 sets of bolts so 
far. I will keep the list posted (so to speak) on whether this 
project will be economically feasible for myself and Specialty 
Automotive, based on being able to move the majority of the first 
batch of 100 sets that I have discussed with the manufacturer.

Thank you, David, for your sound advice below on proper maintenance 
procedures that all should follow on every car. When in doubt, read 
the instructions!