In a structural layup there are indeed overlaps or buts. You have to have overlaps as a 45 ply will generally not be able to cover a mold in one piece. Handalo uses a 2 inch overlap which is fairly large… generally speaking an overlap should be minimum .5" or a little larger. And you should never stack an overlap, there should be at least .5" between laps and/or 4 plys or more between if you do have to stack an overlap. That is for wovens.
Non woven UDs, from what I’ve seen, generally are never overlapped and always butted. I have used laps with UD, but it’s generally not a normal practice in manufacturing. Usually uni parts are highly loaded, like a wing spar, floor i beam, or similiar. The uni parts are also the lightest parts and generally less damage tolerant. I’d imagine that having laps in a highly loaded uni structure could cause issues with creating stress risers… theoretically but, with composites theories are only that. Really if you want to know it takes testing to verify. Though with experience much can be done using simulation.
These are from aerospace manufacturing, which is probably more conservative, as Handalo points out, erring on the side of safety is generally better. These materials are pretty damned amazing though, and I’m continually amazed at the performance of composite parts that are seemingly thin.
