As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER TAKEOFF WHILE ACCELERATING THROUGH 40-50 KTS A MODERATE 1/1 WAS NOTED. IT CONTINUED TO WORSEN WITH AIR SPEED. I TURNED AROUND AT ABOUT 100 KTS. LOWERED COLLECTIVE, AND RETURNED TO BASE. THE SEVERITY OF THE VIBRATION LESSENED WITH LOWER COLLECTIVE SETTINGS. DURING INSPECTION OF AIRCRAFT, FOUND THAT THE LT FLEXURE ASSEMBLY WAS DELAMINATING. REMOVED AND REPLACED FLEXURE ASSEMBLY AND CONTINUED OPERATION CHECK FLIGHT. AIRCRAFT RETURNED TO SERVICE.