To help with directional control on the tailwheel equipped airplane, the pilot landed in grassy area with rough terrain features. While on the landing roll, the airplane's right main landing gear broke and separated from the airplane. Directional control of the airplane was lost, the airplane nosed over, and came to rest in the inverted position. Substantial damage was sustained to the airplane's upper wing and rudder. An examination of the airplane revealed a pre-existing fatigue fracture with interior corrosion of the right landing gear strut, that was not discovered during the previous inspection.