This is not the case. While KE is not conserved, I have yet to find a physics book that says it's converted mostly into thermal energy. However, I have read where most of it's converted into damage to the colliding bodies. I'm not a physics professor but I work next to one as a adjunct math instructor. I'll ask Dr. Hannigton the next time I run into him.
JWP475 it's clear you are not reading the replies in this thread (and others) or the book you reference very closely. I suspect that this will continue.
Also,just because energy is defined in Joules doesn't mean the transfer is to thermal energy.