Chances are some of that wood that you can't split may be elm...and if it is, no amount of "mauling" is going to split it!
Like all the other replies you've gotten, I rip wood all the time. Lay the log on its side, so that the bar is essentially parallel to the log. Then begin cutting with the very back of the bar, with the tip angled slightly up. (Like Troll suggests.) Maintain that angle until you're nearly at the bottom, then level out.
I use the noodles that result as mulch for the gardens. (Throw some bloodmeal on the soil first before you put the wood on so it doesn't eat up all your nitrogen as it decomposes.)
I've never found it to be particularly tough on chains, and I split frozen elm that way. Like the others mention, though...watch that those noodles don't clog your sprocket...you can throw a chain if they do.
I've found ripping wood with the bar perpendicular to the log is much slower and just vibrates the living he!! out of you.