Have you ever held your breath as your phone slips from your fingers and tumbles to the ground? I know I have, and fortunately for me, this story has had a happy ending, my phone has yet to break or crack.
I know that this did not happen by accident, but rather is a marvel of engineering. As high-tech device innovation keeps accelerating, ensuring Device Structural Performance without sacrificing user experience and aesthetics is essential for every new design. For this reason, SIMULIA has developed and delivered the Device Structural Performance Industry Process Experience. As part of that solution, we have run a number of industry-standard phone tests virtually using our Abaqus technology for Structural Simulation. These simulations include a drop test, a three-point bending test, a water-immersion test, and an assembly stress test.
These tests were carefully picked to demonstrate what most SIMULIA phone customers use our simulation software for.
I had the opportunity to interview the principal engineer who designed and tested the phone drop simulation. As I spoke with the engineer I learned step by step how engineers conduct their testing in a virtual space.
First Step: Create a Controlled Scenario
For the phone drop test the Engineer first setup the phone so that is would be dropped onto its corner from a 1m height and at a speed of 4.43 m/s. Through the power of simulation, the Engineer could be certain that the phone would be dropped at the same speed, the same angle, and the same height for every experiment. This assurance allowed the Engineer to change other variables and be confident that those changes would be the only variables effecting the results.
Second Step: Testing Each Variable Change
You will be happy to hear that they did NOT have to drop hundreds of phones for this experiment! Instead, the Engineer was able to change certain characteristics of the phone while rerunning the drop tests. For each drop test, the Engineer observes how much damage had been sustained by the screen on impact.
Here are some of the things they changed when testing which would make the phone the most durable:
- Glass Material
- Thickness of Screen
- Corner Radius
- Thickness of Back Cover
- Thickness of Center Frame
- Screen Protector Lining Width
After running the simulation the designer was able to determine that changing the glass material avoided the hairline crack, but there was still a damage to the bottom right corner. Further optimization had to be done to avoid this.
Third Step: Setup the DOE (Design of Experiments)
When engineers cannot simply change single variables to find their desired design changes they must then move on to the more complex experimentation. Engineers working with simulation have come to the understanding that the common approach of changing one factor at a time is very often incorrect since the way that these variables interact with one another can actually impact the results of the experiment.
For this drop test experiment, the principle engineer ran eight different configurations for their tests. Each configuration has different combinations of variables that are changed.
Before running the simulation, the principal engineer needs to setup the sensors which track the specific focus variables that they want to optimize:
1. Mass of the Model
2. Von Mises Stress of the Plastic
3. Von Mises Stress of the Frame
After running the simulation the principal engineer was able to determine that tests 1, 2, 6, and 7 produced results where there was the least amount of strain on the plastic. Using those different tests, the engineer can also perform a visual inspection of the results.
As you can see above, option six (the far right result) was the only result the did not produce any cracking in the screen.
So here are the before and after results…what do you think? I know which one I would rather have in my pocket, and so do phone manufacturers.
