Removing a broken or sheared bolt or stud is never easy, but if you have a welder (a mig welder is preferred) you can sometimes weld a nut to the end of the broken bolt. The heat generated by the welding process often helps to loosen the bolt and makes removal of the bolt can be achieved very easily with a spanner.
https://www.universalgripco.com/#!astm-e23/zkr7j
A quick strain map video of a Charpy Impact Test performed on an Impact Tester from Universal Grip.