The trick to splitting hardwood, other than avoiding burls and knots, is to shave off chords around the outside of the buck. If you tried radial cuts or splitting on the diameter, well, best of luck with getting a season's wood split in one year. Chords around the circumference for about 50% of the buck, thenif you're lucky the core will split on the diameter.
Also, use a maul with fat cheeks and no edge rather than an axe. It's the right tool for the job.