I was running a simple RBD simulation on some pre-fractured geometry the other day and I ran into some interesting road blocks along the way.
One way to "Activate" an RBD object is to use the "Active Value DOP"
(In my case I had 4 pre-fractured walls that I needed to crumble at specific frames)
Make sure to set this node to "Set Always"
By default it is set to "Use Default"
Now what you can do is keyframe the "Active" value, 0 being not active and 1 being active. It is generally a good practice to make the keyframes Stepped so that the change from inactive to active happens over one frame.
Another node you can use is called the "RBD Keyframe Active" DOP. It can be used for more than just changing the "Active" value but in this case it works perfectly by again, animating the "Active" value.
Theres not much more to it than that. Super simple.
Ironically though, this took me hours and hours to figure out. Originally, I had setup each of the pre-fractured pieces as RBD Packed Glue Objects. This worked perfectly when I tested it on one wall. Basically the theory is the same here, inside your DOP Network there will be a node called (I used the RBD Glue Objects shelf tool) "Glue Constraint Relationship" and on this node you would animate the "Strength" value (making sure to set it to "Set Always").
This value is different because it's not just 0 to 1 like the nodes mentioned above. For instance, a value of -1 will make it completely inactive but a value like 10,000 (the default) would make it active. So I still keyframed it but I made one at -1 (inactive), then I made one at 10,000 (active).
And like I said above, this setup worked perfectly when I only needed to do this to 1 wall. But I had 4 walls that needed to crumble and as soon as I setup a new constraint connection and animated the "Strength" value, as soon as an object would hit the first wall, the second wall would completely disappear.
I still haven't quite figured out why it does that, but after much pain and struggle I eventually decided to just use the "Active Value" DOP that I was talking about earlier.
One thing to note though, is that when I was using the glue setup, it makes an RBD Packed Object node (the one that gets plugged into the Rigid Body Solver). For some reason the "Active Value" DOP does not cooperate with RBD Packed Objects. So to counteract that problem, I just simply made it into a good old fashioned "RBD Fractured Object" and that did the trick.
Hopefully this helps you out. I certainly learned a lot from some painful trial and error.
Maybe in the future I can update this and show you how to fracture an object based on the distance to that object. Cause that sounds like a lot of fun!