First Broken Bow

[Otzi]

I was figuring that the extra depth would handle the strain?

[autologus]

I was figuring that the extra depth would handle the strain?

Depth would help some in compression but not tension, the width of the back and the amount of crown will determine how much tension it can take.  A 4" wide stave with a high crown would not be any better than a 2" wide stave with a flat back as an example.

Grady

[lostarrow]

A crack straight across the grain can only mean rot IMHO. Go snap a branch that's been laying on the ground for a while and compare it to a sapling you try and break.  Observe the difference.There's your answer.

[mikekeswick]

The area has been weakened when you  steamed and corrected it.
Not all elms are equal.

[Pappy]

Looks like dry dry rot to me,if so nothing you could have done about that.I do a bend test on almost all white woods before I start. To bad but it happens from time to time. 
 Pappy

[DarkSoul]

Those corners are also far too sharp! You must round all four corners of the limbs (about the radius of a small pea) before you do any bending whatsoever.
These sharp corners didn't cause the break, but it sure didn't help either.

[Newindian]

i cut some elm a little while back and tryed to make a bow from it while it was still alittle green and it broke the exact same way as yours i started to investigate it an noticed that the sapwood was extreamly brittle and chiped off rather then sliced off