THE AIRPLANE LANDED APPROXIMATELY HALFWAY DOWN THE 3250 FOOT RUNWAY. THE PILOT APPLIED THE HAND BRAKE 3 TIMES, ON THE THIRD TIME THE BRAKES FAILED. THE PILOT TURNED OFF THE RIGHT SIDE OF THE RUNWAY TO SLOW DOWN IN THE GRASS BUT THE AIRPLANE HIT A DITCH AND NOSED OVER. EXAMINATION OF THE BRAKES REVEALED AN INTERNAL FAILURE IN THE BRAKE MASTER CYLINDER.