Negative pressure appearing in examples

[mpellegrino9]

I am running the examples, to try and understand how to do solid mechanics simulations. Both in the codes I write and in some examples, pressure becomes negative. Is this intended?

I ran the TaylorBar example as a demonstration and in the image I'm attaching I made Mayavi show negative and positive values and you can see negative values just at the impact zone and at the top of the bar.