In Ls-Dyna I am simulating low velocity impact on flax composite plate and I am using MAT55. One of the downsides of using this material card is the unrealistic stiffness. Under *Control_Shell I activated LAMSHT (laminated shell theory) and in *Part_Composite I set SHRF to 1. When I run my simulation, upon impact my model disappears. I get a negative Jacobian. However, my simulation terminates normally. Is there something that I am missing when using LAMSHT? Why does my flat plates disappear when impactor first makes contact?

Thank you for the help.