Thread: Just looking for opinions on a broken trailer axle?

looking at the Growth ring type appearance it might have something to do with the hardening process?
I have used an industrial hardener for half shafts and it had a ring pass over the shaft that super heated the steel and it was immediately followed by a coolant to harden the shaft.
or it is something in the steel manufacturing.
Some metallurgist on the forum will have a better idea

That is a classic picture of metal fatigue, nothing abnormal about it, my engineering text books all had pictures like that in them. Typically all you need is a sharp machining mark as a stress raiser and a cyclic stress (all that road shock) and it'll propagate the crack through relatively soft steel. The centre bit clearly had a brittle failure at the end of its life. My guess is that the trailer axle has had a fairly hard life.

https://en.wikipedia.org/wiki/Fatigue_%28material%29



http://materials.open.ac.uk/mem/mem_mf4.htm

Time to upsize that axle!

fairly standard cyclic fatigue failure as already metioned.

somethings induced a failure in the case hardening this has spread around the circumference as the axles flexed, once most/all of the case hardening had fractured away the crack grew inwards and the faces of the "split" have "polished" against each other as the axle flexed acounting for the smoother part of the break, once the fracture had worked through enough of the metal the remaining portion suffered a near instant over load failure and my guess is that the final failure was a tension failure as the axle "bent" up against itself on the loaded side of the split pulling the final section of metal apart (grab a spring type peg and push the legs apart instead of pinching them you'll get what I mean)

I doubt very much the trailer axle has been heat treated. They're just a medium carbon steel. Any pre-installation welding of spring pads, brake mounts etc will destroy the heat treatment.

I would also say that it has had a hard life and fatigued. Usually a big hit (to propagate fracturing) will bend the axle and it's interesting that it snapped in the centre which makes me think it may not have been a stress raiser from a flaw as the crack probably would have run from one side.

As above. Classic fatigue failure, probably resulting from what could be described as a "machining error" leaving an unintended stress raiser. But most likely in reality the result of chronic overloading where either the trailer was consistently overloaded or the axle was undersized.

This type of trailer axle is not intended to be sufficiently heavily loaded that likely machining marks would be a sufficient stress raiser to initiate failure. Of course, there is the possibility that there was a stress raiser that was sufficient introduced by damage to the axle after machining. This could possibly have been from road damage, although the pictures do not make it clear where the break is on the axle. Similarly, it could be the result from welding making a stress raiser.

There is a slight possibility that the stress raiser was an irregularity in steel composition, but there is no indication of this in the pictures, which strongly suggest the stress raiser was at the surface - and note that there is what looks like a machining mark a few millimetres along the axle from the break, and this is the sort of mark that could have started the failure.

John

I would say the machining error was insufficient radius in the corner, between the journal diameter and the face the bearing sits against. The radius should be as big as the bearing will allow.

Cheers, Mick.