another try for Newmark. again no convergence but a nice idea of automation for the coupling between material and kernel...
fixed error in Newmark material. however, no convergence yet.. :-(
completely removed velocity as intermediate variable in newmark scheme - does not help either
and another run for newmark. now exactly following [Subbaraj1988, Table 1]. Seems to converge only because I reduced the density by a factor of 100. - We will see what this means for dynamics.... Furthermore there is a FIXME about the material which ight be evaluated much too often since the kernel computes the acceleration by itself anyway. However, I am not really sure about this. Will need a debugger tomorrow.