Please take a look at "http://www.beam.tv/beamreel/QsxSmnpxys [beam.tv]". It is an advertisement and you can see in this work hailstones are smashed. I wonder how can I make something like that in Houdini. As you see in this work hailstones shattered in many pieces. some of them are big and some of them are very small. I appreciate you time if you take a look to it.

I would start with a rather simple particle simulation, grid, birth particles, gravity force. Collision with ground plane. Add a on hit attribute. Then copy sphere on it, use pscale to vary the size. Then use the shatter SOP. You can shatter all or use an attribute again to just shatter some of the particles.

thank you pagefan for your time and reply. I will do what you have said and I think it will work . . but the problem is in render time. if you copy spheres to particles and then shatter them the morphology of hail stone will be globular at render. as you can see in this advertisement the hailstone is more similar to particle fluid surface before hitting the ground so you see it has very smooth surface.
I think it should be some works with particle fluids but in particle fluids I can not create such variation in size and shape of particles :cry:

Well if you have a close look at the shots you don't see an awful long animation of the fluids, just a few seconds max. So that is only a 28 frame simulation.

In case of the first exploding hail shot at 8", you see one hail stone being scattered in some large chunks and then a lot of smaller stuff. It doesn't really flow but more shoots out of chunks of the base hailstone. So you could do a shatter sop, put that in dops, let the hailstone shatter, select some of the chunks to drive the particle simulation further and use those chunks either as a container for a particle fluid or try to birth particles from them. In the popnet, lay down a source node and then use birth from volume as option.

very nice …Thank you very much Pagefan I think it works… I will try it. I am not as professional as you but I will do my best…