Thanks for the prompt reply.
I have had a look under both time/frequency viscoelasticity and *viscoelastic in the ABAQUS manual but this is not what I was after.
I probably should have made it more clear in my OP that I am trying to reproduce some test data which involves compression testing where the increase of elastic modulus was observed as strain rate increased. So my plan was to make a material model with the increase in the modulus to see if I get the same stress-strain response.