Everyone has their own methods of Joint Locking and dislocating. I happen to study 4 different Jujutsu styles and they all approach this differently. Now......I believe it is how you apply the lock, at what angle you do it, and how you move your body with the lock. Simply, look at a downward block, which could be a wrist lock. If you apply the wrist to the attacker, and step back to an angle say 45' to the attacker, he most likely will not be able to keep his body up to the lock, and bingo you have dislocation or break. One of my Arts, San Jitsu Ryu, stresses breaking of the bones as well and employs spiral breaks vs. straight clean breaks. This is acheived by rotation of the joint and the angle taken and the movement of your body. Doing any body movement, like going into a cat stance with a lock, does more damage to the wrist because you are dropping your weight, then the angles come into play.
It is hard to say how much torque or power is needed for dislocation or breaks as in case of the dislocation, flexibility of the attacker comes into play. I have though see very flexible people and people who resist technique, drop to their knees when a lock is performed at the proper angle to them and moving your body and establishing a strong base.