The easiest way to facilitate the bending process of the drywall sheets is to lay them on a concrete floor (such as the garage floor) and to wet them with a roller. In addition, if the drywall still doesn’t want to bend, a sponge may be used to facilitate the process. Too much water could easily damage the boards, so professional help is recommended, applying wetness gradually to the inside face of the curve.
If the radius is very tight, two layers of 1/4” drywall can be used as it is very flexible, or a method known as “scoring” could be used. Cutting the paper layer on one side of the sheet allows it to bend it easily, while the other layer of paper on the other side holds the sheet together.