AWS D1.1:2004 has all of the critical dimensions see Figure 4.15 for a guided bend test jig.
Here is one we built several years ago using a 12Ton bottle jack...
http://img.photobucket.com/albums/v345/jwright650/welding%20pictures/Dsc00047.jpg
http://img.photobucket.com/albums/v345/jwright650/welding%20pictures/Dsc00048.jpg
You didn't mention a specific code....
John Wright