As far as I know there's no randomness in what something unravels into. If you have enough imbuing, the item id skill will tell you what something will become if you unravel it. It's calculated from the total intensity of the item.
For relic fragments need about ~451 total intensity (there is some variation according to which soulforge you use, crafted properties are nerfed a little and possibly a few other variables - I have a vague understanding not a complete one).
There are some lists around of what each artifact unravels into (usually relic fragments but some are merely essence) - the crafter's forum has an imbuing FAQ which might be useful:
http://vboards.stratics.com/showthread.php?t=160932
I hope that helps.