[greybeard]

Hi Eson.
I have had a little experience of this, and I believe that the mechanism is one of chemical attack on the acrylic rather than a physical one.
Under stress, many plastic materials are attacked by solvents that in normal circumstances have no effect.
I noticed this many years ago when embedding acrylic fibres as light guides through polyerster casting resins.
Straight fibres are unaffected by the various additives in the resin(mainly styrene monomer) but if I pre-bent a fibre with heat, then embedded it, it promptly dissolved in the area of the bend. I did several experiments with different resin/fibre combinations and the effect was always present if there was any stress in the fibre, locked in by previous treatment, or during the casting process.

John

[Geof]

Greybeard has it correct; it is a stress cracking phenomenon. Acrylic, Perspex, Plexiglas, whatever the name is very susceptible to this, particularly extruded acrylic.

[greybeard]

Geof, I wish you had been around when I was spending hours trying to find out why the light went into one end of the fibre but didn't come out the other !
I'd never come across the phenomenon, and it was a pretty frustrating period.
I did manage to cut 3mm leds down to 1mm cubes to embed in the same project, but the failure of the fibres was the last straw.
The project ? A fan with embedded chips and optics to produce a "firework display" across the surface five seconds after you opened it.
Happy days...!

John