[sandworm101]

>> The reports all mention that the crack became visible suddenly and for no apparent reason, after the headsets had been connected to the external battery pack and stored overnight (some in Apple's Travel Case) with the soft front cover attached.

It is glass. The device was being charged, which means some heat gradient between the charging battery and the outside world. That thin 3d-shaped glass cracks under thermal stress should be no great surprise.

[reaperman]

> That thin glass cracks under thermal stress should be no great surprise.

Actually, the thinner the glass is, the less likely it is to crack due to thermal gradients. It is thicker glass which experiences greater stress. The equation for thermal stress is:

thermal_stress = (coefficient of thermal expansion) ∙ Young’s modulus ∙ ∆T

which for glass, works out to about 0.63 MPa per 1 degC temperature difference between the centre and edge of the glass. Thinner glass has less temperature difference, so lower stress. Furthermore, surface roughness and type of imperfections lower the amount of stress needed to cause a failure, so Apple's obsessive polishing makes the glass withstand higher stress than usual.

[brookst]

Thanks for the info and model! But if the thin glass is bonded to the aluminum frame by glue, would that not change the calculus? If we imagine hot air on one side of the thin glass and cold aluminum on the other?

I’m very skeptical of the “charging thermals cause cracks” theory, seems more likely that minor manufacturing defects might do so when the headset cools from a session. But I suppose we’ll hear more than we want to in the next few weeks.

[layer8]

> The device was being charged

The external battery pack is the only battery, there is no internal one being charged. There is also no mention of the external battery being charged.

[nickthegreek]

Maybe no surprise to Apple, but it is certainly a surprise to the purchases who shelled out $3,500.

[reaperman]

> Maybe no surprise to Apple

It would be a huge surprise for Apple if a lithium battery inside the visor caused the cracks, as they did not design the head unit to include any internal battery.

[asadotzler]

There isn't a significant battery inside the visor. Unplug the external battery pack you keep in your pocket and see what happens.

[reaperman]

I would need someone else to tell me because I'm not buying a $3,000 toy.

[amelius]

Maybe they placed the visor near or on top of the battery while it was charging?

[iAMkenough]

There's no battery behind that glass, so it's the processors or another component generating heat while stored.

[nottorp]

> Given that the battery is external to the headset, any heat generated would presumably need to be caused by a background software process gone haywire.

Apple is very good at background software processes taking 100%-500% cpu (100% == one core in Apple land).

[sandworm101]

>> The reports all mention that the crack became visible suddenly and for no apparent reason, after the headsets had been connected to the external battery pack and stored overnight (some in Apple's Travel Case) with the soft front cover attached.

The battery is external, but mobile. The users may well have stored it inside the thing. Plus, it is understood that this device continues to draw power while not in use, which also suggests a possible thermal gradiant.

[reaperman]

IIUC there's no lithium battery inside the Apple Vision Pro at all. The power for it is supplied by an external batter connected via USB cable.

[givinguflac]

If it had cracked while in use, perhaps due to the processors heating, but the battery is external to the device, so I don’t see how that’s relevant. I suspect a manufacturing defect personally, given that the heat comes from the computer inside and not the battery.