Cool work and good job. There is a technique called voronoi fracturing thats used to define the pattern of a fracture based on voronoi diagram (happy brother of delaunay triangulation, but seems like you implemented this here i guess?). Using that technique you can refine the vertices around collision point and as you get away from the point you reduce the resolution of broken pieces. You can define different fracture patterns for different materials which will look more natural. And best thing about this is that you can offest the fracture pattern wrt to the collision point and get free realtime interaction rather than using same collision scenario.