40 mins is tight for any international flight connection (YMMV) ... You may make the flight leaping thorough the terminal like "Ole OJ" in the Hertz commercials back in the day, but there is no guarantee that your bags will make it. Pack a days worth of clothing and necessary toiletries in your carry-on just in case. Depending on your medallion status, make sure the put priority tags on your bags and check your itinerary diligently in the weeks and days leading up to your departure. Last minute departure time/equipment changes seem to occur more frequently as of late and of course on the Delta weekly "schedule change saturdays". I would even look at the 10 day weather forecast leading up to your flight to make sure your inbound flight to ORD is on time as well. Lots of variables at play. Be sure and update us here on the forum after your trip. Happy flying!