How does the surface area of a piece of glass (or any general material; sapphire isn't technically glass) correlate with strength? Strength as in resistance to pressure concentrated at a small point?
Intuitively, something tells me that the larger a piece of glass is, the less resistant it will be to pressure at a small point. Take the extreme example. A "piece" of glass that consists of one molecule. Applying pressure to this one molecule won't fracture the molecule. (But then perhaps this example is too extreme).
I ask because of this comparison, done with a sheet of sapphire "glass" that is clearly much larger than the other, competing piece of glass. Would the size of the sapphire give it an inherent disadvantage in this test?
Here is a video of the complete test: https://www.youtube.com/watch?v=u6B-2jTvh1w
Best Answer
Yes, you're right that sample sizes need to be standardized in strength tests. In the picture you included, we see a ring-on-ring strength test. A small ring on top presses against a sample of uniform thickness resting on a larger ring. The loading is (up to second order effects) localized within the disc-shaped area of the sample located above the lower ring. By applying standardized ring diameters and standardized sample thicknesses (here 1 mm), unbiased comparisons are achieved.