Learning Forum

[Fence14]

I'm moodeling a phone droptest to study the impact of having a phone case. I've been using the explicit dynamics material: Rubber1. Is this a decent choice or is there a better rubber that is more typical for a phone case?

[Raef.Kobeissi]

Hello Check the properties of the different materials and pick the material that has the best physical properties.

Regards

[peteroznewman]

I have seen two types of phone cases: thick rubber cases and thin plastic cases. The thin plastic cases are far more popular.

PLASTIC

The plastic is polycarbonate and I see there is an Explicit material called POLYCARB that has plasticity defined. The material description says the data came from this paper, but doesn't say which strain rate. Here is the figure for PC from that paper. I have a matlab utility called grabit that makes it easy to digitize data points from graphs like this. I digitized the highest strain rate curve and it doesn't match the ANSYS data very well, which extrapolates out to a strain of 0.7.

What will the strain rate be for your drop test? You might have to run a simulation with a first guess, and see what the strain rate is, then pick a different curve and rerun the simulation since there is a significant difference between the highest and the lowest strain rate.

RUBBER

I took a look at Rubber1 in the Explicit Materials but it has no strain rate dependence (though I haven't yet read how the EOS equations work). I found this paper that has strain rate dependence for various rubbers. As you can see in Figure 17 below, there is a large strain rate effect for this EPDM rubber. Note that this curve is in Engineering Stress and Strain, while the curve above for PC is in True Stress and Strain. I wrote about how to convert from the first to the second in this discussion.

Just for fun, I made a 20 mm diameter Rubber1 ball and did a 1 m drop test and it bounced, as expected. 

https://youtu.be/105vAj6rAtE

 

Good luck with your study.

Regards,

Peter