Failed Lift Tag Axle, 1997 WB (youtube)

[davidbrady]

(04-03-2019 10:02)ernie ekberg Wrote:  wonder how it broke?

Hi Ernie, To put some numbers to it, here's my envelope drawing for loads, shear, and moments:
  1997WB_TagShearMoment.pdf (Size: 296.61 KB / Downloads: 520)

The max bending stress is: s = M/Z where M is the max moment, Z is the section modulus and for a 5" diameter tube with 0.5" wall thickness Z = 7.25, which gives us a max stress (s) of s = 80,000/7.25 = 11034 psi. Suspensions are built to handle 3G of vertical load. This simple analysis shows this axle has the required safety factor and stays clear of the metal fatigue limit during normal driving which is less than half its UTS (Ultimate Tensile Strength), or around 32000 psi for mild carbon steel. IOWs, something else is going on.