On Mon, 10 Aug 2020 10:30:38 +0100, Martin Brown
wrote:

On 08/08/2020 12:23, Pinnerite wrote:
I have some cast aluminium garden chairs.
The screw holding one of the arms got loose and I forgot to tighten it.

Yesterday the top of the arm snapped off, leaving the screw in place.

snip

I am somewhat mystified how a loose screw could make
the arm snap off.

By allowing excessive bending moment over the remaining material?

I doubt you will be able to make a good enough bond to
last very long in service unless you can add some strengthening as well.

Whilst you may be right, it could all depend on what the loads are on
the joint under correct circumstances?

eg. If the arm would only typically see load 'n' but with the screw
loose, a part of the arm that may not normally carry much load got
'10n' (causing it to fail). As long as the chemical bond will take the
straight 'n' then all could be well?

Ideally, the break has happened at an angle to the normal load and
hence mitigating the load on the repair joint to some degree.

Cheers, T i m