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Brass Cylinder Shear Failure
3

Brass Cylinder Shear Failure

Brass Cylinder Shear Failure

(OP)
Hello,

I'm recently had a few shear failures for a turned brass H59 part (see the link below for an image). My gut tells me that it's a material defect, since we've made over 10k of these prior and only just started seeing this failure mode. Does this make sense? Has anyone seen this before, and if so, do you have a theory as to what specifically about the material might be defective? I'd really appreciate any feedback here:)

https://drive.google.com/file/d/1EUNH47lgtO2biB-Ev...

RE: Brass Cylinder Shear Failure

It doesn't look sheared, except that most failures end up along a shear plane - it looks like some large bending force was applied and it peeled the threaded portion off the flanged section. Notice that there is a deep vee on the right image at the 12 o'clock position that reverses towards the 6 o'clock position.

Maybe someone sharpened the tool a little extra and removed a small fillet? This can easily form a very high stress concentration.

Without knowing the loads and operating conditions, it could be anything. You should be able to do a hardness test on an old one and the failed one to see if the latest material is weaker or send samples of old and new out to a metallurgical lab for a more exhaustive comparison.

It's also not unlikely for a material supplier to exceed the requirements for a long time and then there is a change in supplier or a change in process to make material that conforms to the spec but has worse properties, a condition you may have been unaware of.

RE: Brass Cylinder Shear Failure

Had a quick look at the picture and noticed the location of the failure. Although, as previously said, there are unknown loading conditions included, such a component would usually have what is known as a ‘thread undercut analysis’ carried out (also known as Kowalski’s Method/ Formula). Due to thread radial loading, as a result of preload and in service loading, the end of the cylinder would be pushed radially inwards, putting the outer surface at the kt affected undercut (at last thread and at thickness step) into tension and bending. Such analysis may help in understanding the potential stress levels?

RE: Brass Cylinder Shear Failure

Why is that thread undercut deeper than it needs to be and why are there no stress relief fillets ?

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