Experimental techniques for evaluation of fatigue characteristics of laminated constructions from composite materials: Full-scale testing of the helicopter rotor blades

Abstract

The importance of full-scale testing in the development process for composite laminated materials helicopter blades is discussed and illustrated by means of two examples drawn from the Aeronautical Department, Faculty of Mechanical Engineering's experience in the use of composites in a wide variety of structural applications. Laboratory fatigue testing is conducted at the Aeronautical Department on all flight-critical dynamic components in order to determine structural adequacy. In this paper, the analyses of behavior by fatigue testing for a main rotor blade for a light multipurpose helicopter propulsion system and a heavy transport helicopter tail rotor blade of composite laminated materials are given. The blades were fabricated from composite laminated materials. The contour of airfoil was formed by a continuous structural pocket, which had a Rohacell foam core and a fiberglass skin. The upper and lower skins were fabricated from woven fiberglass that was laid up with fibers oriented at 45° and 0°/90° to the blade's longitudinal axis. In the trailing edge of both skins, graphite fibers were placed for stiffening. Fatigue testing of the helicopter blades was accomplished in a special test facility designed to simulate the inflight loading. The applied test loads include simulated steady centrifugal, vibratory chordwise bending, vibratory flapwise bending, and vibratory torsional pitch motion. The fatigue analyses of these composite laminated structures were performed after fatigue test cycles for the detection of laminate separation, tolerance, and distortion of structure cross sections. Copyright © 1996-2011 ASTM.