用户自定义子程序，umat, user subrouine 的实现步骤

1）The first place to start, for information on how to implement a user material model, would be to read Appendix A of the LS-DYNA Manual. I trust you will have either a hard copy or a pdf. 2）Secondly, you will need a linkable version of DYNA for whatever platform you are running on. What you end up doing is writting your own Fortran material subroutine which is then compiled and linked with the rest of the DYNA object code. You will probably have to directly request a tarball from LSTC. There are also some examples on user material models available on the ftp site， which might prove helpful. Hopefully, this is enough to get you started. If you begin trying to do things above and beyond what is described in Appendix A and the ftp files (such as element deletion, or passing curves to the subroutine, etc) then things can get more complicated, but are still possible.