Learning Forum

[Sasi Kumar Tippabhotla]

I am trying to understand how the usercreep.F subroutine, given in the Ansys customize folder (........\ANSYS Inc\\ansys\customize\user), shown in the attached screenshot. I am unclear of the following aspects and need help to understand

1. Is this explicit or implicit formulation?
2. If explicit, is the logic written for "delcr" corresponding to the first and second if-constructs correct? The double exponential on the RHS seems to be wrong to me. Or do I miss anything here?
3. If, implicit, I not able to comprehend at all. Please help me to understand the logic and if possible direct me to the theory help in Ansys documents. I searched the ansys theory manuals and did not find anything related to the implicit formulation of the primary creep equation.

 

Thanks & regards,

Sasi Kumar

[John Doyle]

The usercreep.F routine, given in the Ansys customized folder, is written in FORTRAN for implicit strain hardening primary creep (TBOPT=1).  See Table 4.2 of Section 4.5.5.1 of the MAPDL Material Reference Guide.

I would refer you to the MAPDL  Programmer's Reference (ansys.com) for more details.

[Sasi Kumar Tippabhotla]

Hi John, thank you for your response. My question is not about how the usercreep subroutine works. I understabd that it is based on strain hardening model of primary creep. May be my question in the original post is unclear. Let me elaborate.

I am trying to understand the implicit formulation of the creep function here. To be specific, I am trying to understand the calculation logic used for "delcr". If it is an implicit formulation (I guess it is),

delcr = e_cr(n+1) - e_cr(n) = C1*(sigma(n+1)^C2)*(e_cr(n+1)^C3)*exp(-C4/T(n+1))*delta_t

where n indicates the current time step and delta_t = t(n+1)-t(n). I expect the formulation integrates the creep function to eliminate the (n+1) terms and solve for the delcr. That is why there is a long "if-else" logic to address different scenarios. I am not able to understand how the eauations used for "delcr" calculations are arrived at. Explanation of the same is not available in the theory manual or user programmer's guide