dc motor winding will be burn.

When ac supply is ginen to DC motor, DC motor will run with 
less speed and prodeced some noice.

AC apply to DCmotor frequency dependent losses increse 
(eddycurrent&core)losses
motor gives less output

if A.c supply given to D.c motor more spark at brush & run 
at low speed with noise

if A.c. supply given to D.c. motor the net torqe will be 
zero and motor will not work. bez postive &negative cycle 
is zero.