One of the accessories carried around daily in this product is a water-filled plastic tube. Since it is carried around, surviving a 15 inch (38 cm) drop was one of the requirements it had to pass. A physical test demonstrated that the initial design failed the drop test.

Physical test

I built a transient dynamics model of the initial design to show that the part was predicted to fail, which was some evidence that the model was valid. The water was modeled as an orthotropic solid.

Drop test 2

Plotting the peak stress showed that the maximum stress in the model exceeded the ultimate strength of the material.


I went through many design iterations to find a few designs that were predicted to survive the drop test such as this one, which reached a peak stress of 49 MPa at 0.5 ms after impact.



Here is a link to a Microsoft Powerpoint 2013 file that has a summary report including the properties of water and some videos of the simulations.