Joint.breakForce
var breakForce: float;
Description

The force that needs to be applied for this joint to break.

The force might come from collisions with other objects, forces applied with rigidbody.AddTorque or from other joints. See Also: Joint.OnJointBreak.
	// Makes the joint break when a force larger than 10 is applied
	hingeJoint.breakForce = 10;
	// Makes the joint unbreakable
	hingeJoint.breakForce = Mathf.Infinity;