Earlier today, we shared a video of what appeared to be the front panel of the 4.7-inch iPhone 6 subjected to a limited bending stress test, but YouTube user Marques Brownlee has now acquired the same front panel and subjected it to additional stress tests, including more significant bending and scratching.

In the video, Brownlee scratches and stabs at the panel with a set of keys and a knife, but is unable to cause any discernible damage to the display. He then goes on to bend it quite forcefully, both with his hands and under a shoe, but the panel does not break.

Though Brownlee describes the front panel as being made of sapphire crystal in his video, there is no way to confirm that the panel, which has been seen in previous videos and images, is indeed made of sapphire. Corning's Gorilla Glass , which is currently used in iOS devices, also has many of the same properties -- it is both highly scratch resistant and somewhat flexible.

Rumors have suggested Apple plans to utilize a sapphire display in the iPhone 6 for increased durability and scratch resistance, but it has also been suggested that sapphire could be limited to the larger 5.5-inch iPhone 6 due to supply constraints. In that case, the front panel of the 4.7-inch iPhone 6 would likely continue to use Gorilla Glass.

Apple's 4.7-inch iPhone is expected to be released this fall, likely in September. A larger 5.5-inch iPhone is also in the works, but it is unknown whether the device will launch alongside the 4.7-inch version or later in the year. Both devices are said to include an A8 processor and camera improvements.