Thank u guys
Using spheres for collision between two bones is ok.But how to detect direction of the object hit.Example(object is standing and facing north direction i am punching the object from south direction(behind)).
Imagine your character is constructed of spheres. For instance 4 intersecting spheres for the forearm; a couple of sphere for the upper chest so forth. You can then group those spheres into a hierarchy by body parts. For instance you can put a sphere around the forearm that contains the four other spheres. This is not a collision sphere it's simply a container for the others and is used for a rough check. In the same way you have a sphere around the entire character. You just have to make sure it's big enough so your character animations don't cause any sub-spheres to go outside of it. Doing it this way you don't use bounding boxes at all; AABB or otherwise. I use a similar system for my terrain and it works well.
Spheres are nice in 3D because it is inherently easy to calculate collisions between them. If you increase the radius of one sphere by the one you are checking it with, you now have a point sphere collision test. You can then sweep a point by some increment according to your animation to do the collision. Keep in mind that checking two moving objects is the same as holding one steady and moving the other one. It's all relative.
As for the direction of the hit, if a point hits a sphere simply generate a vector from the centre of the sphere to the contact point.
There are a lot of details to all this. Doing full 3D animated characters with real collisions is non-trivial. Check out http://www.naturalmotion.com/ for some truly impressive stuff. Good luck.