In the paper I sent you,
You can see a shear modulus of 0.85 MPa and a SIGY of 0.22 MPa. SIGY is relativley high compared to the shear modulus allowing probably in this case some elastic deformation. If you have a shear modulus really high compared to SIGY you probably have less elastic deformation and quickly go to plastic deformation.
How do the values you are using compare to the ones from the paper ?
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