Social media and the iPhone Duo subreddit are filled with reports of Apple's foldable failing quickly, sometimes after only a few hours of use. Users describe the hinge catching on something before audibly cracking and breaking the screen, with the cracks appearing in the same place across different devices.
YouTuber CuriousHagi was able to reproduce the cracked screen during durability testing of the iPhone Duo. He then pulled the phone apart to investigate. What he found was that the Duo's hinge is quite complex, consisting of a gear-like central hinge and two different types of linking hinges.
The teardown points to that hinge mechanism as a likely cause of the failures, though the full findings were not detailed in the report. Apple has not commented on the issue.
