Originally Posted by Dr Phil mmkay
That obviously says improper installation. The bar clamp on the stem was obviously over-torqued (a Park Tool torque wrench goes for 30-40 bucks online).
Sorry for sounding disingenuous, I was going to make a long and detailed argument over the merits of carbon and aluminum materials in failures but didn't want to a long drawn out thread. Oops.
I don't see anything to indicate improper stem clamp torque there. Pretty clearly broke far away from the stem.