Strange Mesh problem in Split Hopkinson Bar modelling

Hello,

 

I'm doing Split Hopkinson Bar simulation with Radioss, as depicted below in Fig. 1, I refine the mesh in the middle of the incident bar in order to use them as strain gauge to measure strain signals. But when I conduct the simulation, the strain propagation stops and reflects when it spreads to the refined mesh(Fig.2). And the coarse elements pass through the refined elements.

However, the strain can spread to the end of the incident bar when I mesh the bar with the same coarse elements.

 

It's so strange because I only refine a small part of the bar mesh, in order to measure the precise strain signal (I can't refine all the mesh because of the calculation efficiency). Could someone figure out where the problem is? Any help would be appreciated.

 

Best

 

                                                                           Fig. 1

                                                                     Fig. 2

                                           Fig. 3