How to simulate soft contact using DART engine

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Hi everyone,

I'm trying to simulate a deformable terrain for testing a soft contact between robot and ground. After some research, I found that DART has a "soft_contact" property which may do the job. I tried changing parameter of soft_contact in the sdf file, but nothing changes in gazebo. To be specific, I create one layer and add "soft contact" tag in its sdf file. I change the stiffness value from 100 to 1 and put one sphere on the layer in gazebo (with DART engine). I expected the layer will have different deformation with different stiffness value, but the sphere doesn't sink in the layer no matter what value I set.

Does anyone know how to simulate this kind soft contact using DART (or other engine)? Hope I was clear.

Thanks