I often find that people just want to know what is implied by a designation of "10D radius bends". If that is all you are after, then it only means that the radius of the bend at the centerline of the pipe is ten times the nominal pipe diameter. So, for 8 inch pipe a 10D radius bend would have an 80 inch bend radius at the centerline, the bend radius at the inside would be less by half of 8.625 inches and the outside would be bigger by the same amount.
If you are looking for something else, you'll need to expand your question like racookpe1978 suggested.
David