Jump to content

Got a crack


Tony
 Share

Recommended Posts

Rim flange failure can be due to fatigue initiated from pits at the surface caused by exposure to chlorides (like the rock salt we put on the roads) and propagated as a result of cyclic stress and hoop stress from the loads imposed on the rim from normal use (all influenced by tyre pressure, vehicle weight, cornering loads etc. etc.). :)

Dunno if the Merc wheels are die cast or roll forged? The AMG rims are roll forged. The forged would be more resistant to the failure mode.

Link to comment
Share on other sites

Rim flange failure can be due to fatigue initiated from pits at the surface caused by exposure to chlorides (like the rock salt we put on the roads) and propagated as a result of cyclic stress and hoop stress from the loads imposed on the rim from normal use (all influenced by tyre pressure, vehicle weight, cornering loads etc. etc.). :)

Dunno if the Merc wheels are die cast or roll forged? The AMG rims are roll forged. The forged would be more resistant to the failure mode.

 

Nail and head spring to mind...

Link to comment
Share on other sites

Oh so it was corrosion? That's interesting, always thought that just sits on the surface but it makes sense that it could eat through the wheel.

 

I think only the AMG ones are forged.

 

It's not that it eats through the wheel. Any kind of imperfection can act a "stress raiser" i.e. it has the effect of causing a much higher level of localised stress at a particular point. In situations where the load on a component is cycling, as it is a wheel, the raised stress level at the point of imperfection causes fatigue to set in earlier at that point. The crack is initiated because of this fatigue and once it starts it accelerates rapidly to failure.

 

Other factors can give rise to a stress raiser e.g. a groove left by poor machining, or too small a radius at the intersection between two surfaces. Fatigue induced cracking can occur in components that appear, on the face of it, to be adequately strong to support the load that they carry and good design involves the careful avoidance of stress raisers.

Link to comment
Share on other sites

I'll go with stress fatigue, can be high duty cyclic loadings, even without any stress raiser. Could be some age hardening depending on the material.

 

The experience with BMW wheels with RFTs, show rims can crack like that, sometimes several places around the rim, (seen seven cracks on one inner edge) so suggesting loadings are far too high for the expected life cycle.

 

HighlandPete

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...