Building a smartphone that can take a fall

Aesthetic reasons aside, is there a case to be made for using a smartphone case?
I wondered this after I dropped my naked iPhone 5 on my hard marble kitchen floor. Four times. And each time, the uncased iPhone made it out alive, unbroken, with barely a scratch.

It made me think that perhaps the glass used on smartphone screens has become so strong that buying a case for a phone - unless you’re a careless teenager, or want to make a fashion statement - has become an unnecessary luxury, as useless as an extended warranty.

The likelihood that a phone’s screen will shatter depends on a number of factors, experts say. The device’s weight, the type of material used for the screen and the angle at which it hits a surface, as well as the kind of surface, all play a part.

My iPhone display has most likely never shattered because its entire screen surface hit another flat surface - my smooth, albeit hard, kitchen floor. The energy of that impact was transmitted across the screen rather than in a single spot. But I wouldn’t have been so lucky if only a corner of the phone had hit the floor.

“If a device lands on a corner, there’s lots of pressure in one point and a lot of damage will occur,” said Yang Yang, the director of the Nano Renewable Energy Center at the University of California, Los Angeles. He described my iPhone’s flat fall as a “perfect landing.”

When an electronic device falls on a rough surface like asphalt, cracking is much more likely, said Jeffrey Evenson, a senior vice president at Corning. Corning makes Gorilla Glass, a popular toughened glass material used in many smartphones, including those made by Apple and Samsung.

When a device falls on a rough surface, the impact is not absorbed evenly; rather, it is concentrated where peaks in the surface material hit distinct parts of the device’s screen, drawing more energy into smaller areas. When that energy reaches the material’s breaking point, the screen will shatter.

Properly made cases can help limit damage, but they are still no guarantee that a device will survive a fall.

The larger the device, the thicker the case material needs to be. That is because the force at which an object hits another equals its mass multiplied by its acceleration. Therefore, the larger the device - the greater its mass - the greater the force, and the more protection needed.

The best protection can be achieved by using two types of material in a case: soft on the outside to absorb a blow, and hard on the inside, said Brian Thomas, chief executive of Otter Products, a case manufacturer. Still, design compromises are often made based on consumer need. Otter, for example, makes cases that are hard on the outside to let consumers more easily slide a device into a pocket.

Even if a device has survived multiple drops, often hidden damage has occurred, increasing the chance of an eventual catastrophic failure. Small scratches in the screen material may be imperceptible, but a surfeit of them weakens the overall strength of the glass. That leads to a point where even a device that experiences a “perfect landing,” falling flat on a smooth surface, could shatter, while a pristine, scratch-free screen falling the same way might not.

Corning works to make its Gorilla Glass highly resistant to scratching. Evenson said the current version, Gorilla Glass 3, had reduced visible scratches by 40 percent compared with its predecessor, while tripling the amount of force needed to crack the material.
If a screen could be scratch-resistant, it could significantly decrease the risk of shattering.

That is why the industry is excited about the possibility of using sapphire, rather than glass, as a screen. Sapphire is almost as hard as diamond, the world’s hardest material.
Still, for many consumers, Gorilla Glass and perhaps rival materials may be all the strength their smartphones or other digital devices need to withstand bad behavior.

“We are at the point where the vast majority of smartphone users do not need a case,” said Evenson of Corning.

Just don’t tell that to your teenage child.