I'm new to Houdini. I've just started using Houdini 12 for rigid body fracture simulations , and i have difficulty in shading the interior and exterior parts of the fractured geometry with two different shaders. When fracturing objects in houdini 11 , it creates seperate primitive groups for interior and exterior parts. But i cant find the same in houdini 12.

YOu just need to create groups, look under Group tab.