I always thought that dents could be popped out and that it would not affect the structural integrity of the frame, but perhaps I'm wrong.
i think it will be a sandwich shape
Little dings in aluminum do not hurt frame integrityLarger dents can be ok unless the metal is 'creased' When aluminum gets stressed past the 'modulus of elasticity', or the point at which it the metal can return to its original shape, the metal tends to fracture rather than bendWhat happens then is that attempting to put it back to its original shape will tear the fracture furtherDo not attempt to pop a dent out of an aluminum frameTubes in aluminum frames cannot be replaced (well, they can, but good luck finding a frame builder willing to risk it.) In short - aluminum frames cannot be repaired when damaged, but not all damage is cataostrophic to the frameWhen you see an aluminum tube with a 'crease' type of bend, the structural integrity of the tube has been compromised to the point where it's basically useless Dents in sheet aluminum can be popped out, but the elemental structure of a sheet versus a tube is generally quite differentThe alloys used in sheet aluminum are designed to be formed, pressed, and stamped, and can be worked back into shapeBike frames are made of alloys that are drawn into tubes with the intent of being exceptionally rigidOnce these tubes are formed, they do not respond well to being worked other than cutting and weldingI've always been told that if the dent is less than 1/4 the diameter of the tube and it is _not_ creased, the frame is ok to rideWhat you need to watch out for is a stress fracture around the dentIf you see a crack develop, just throw the frame awayI've ridden with guys who have rather significant dents in their aluminum frames (MTB) but the tube wasn't creased.
