What was found
ON TAKEOFF ROLL AT OAK EN ROUTE FOR LAS FELT A STRONG VIBRATION NR 1 ENGINE, REJECTED TAKEOFF AT 50 KTS AND PULLED OFF ONTO TAXIWAY WHERE EMERGENCY EQUIPMENT INSPECTED THE AIRCRAFT. TAXIED BACK TO GATE USING NR 2 ENGINE. MAINTENANCE REMOVED AND REPLACED NR 1 ENGINE IAW T/C R5M71002, FUNCTIONAL CHECK GOOD IAW T/C F5M71002.**SUPP** VENDOR TEARDOWN OF ENGINE S/N 702980 FOUND SECOND STAGE TURBINE BLADES FRACTURED BY AN APPARENT STRESS RUPTURE OR TENSILE OVERLOAD, IT WAS NOT POSSIBLE TO IDENTIFY PRIMARY FRACTURE. THIRD STAGE TURBINE BLADES EXHIBITED SIMILAR CHARACTERISTICS ALSO WITH NO IDENTIFIABLE PRIMARY FRACTURE.