Nonlinear viscoelastic VUMAT bug fix, Abaqus
Budget: $30 – $250 USD
I have developed a nonlinear viscoelastic VUMAT for a Kelvin unit connected to a spring (Brugers model without the Maxwell dashpot). It works fine for loading but there is incorrect (smaller than it should be) delayed strain recovery during unloading (constant stress in each loading/unloading step). I need someone with extensive experience in developing viscoelastic VUMAT to fix the subroutine. It may need corotational formulation that I have not used.
P.s. I have simulated a uniaxial compression with 7MPa load applied in 0.3s and kept constant for 20s and then for the unloading, the load is dropped to 0.07 MPa in 0.1s and kept constant for 20s.
obviously, the transverse strains should increase during loading and reduce during unloading. In the loading phase, they increase but during unloading, they reduce for some time and then start increasing.
P.s. I have simulated a uniaxial compression with 7MPa load applied in 0.3s and kept constant for 20s and then for the unloading, the load is dropped to 0.07 MPa in 0.1s and kept constant for 20s.
obviously, the transverse strains should increase during loading and reduce during unloading. In the loading phase, they increase but during unloading, they reduce for some time and then start increasing.