Stress distribution and deformation in a twisted blade under combined tension and torsion

Abstract

A theoretical and experimental investigation of the stress distribution and deformation of twisted blades under combined tension and torsion was conducted by LCDR Lawrence M. Hogan, USN, at the Aeronautical Engineering Department of the U. S. Naval Postgraduate School, Monterey, California. Theoretical expressions were developed to relate the deformation of a twisted "blade" of rectangular cross section and constant rate of twist to an applied load and moment. These expressions were found to be linear for the rates of twist investigated and depended only on the blade material and geometry. The theoretical strain distribution was found to be essentially parabolic across the chord, with the shape determined by the initial twist rate and the angular deformation. The experimental investigation was conducted with three specimens of constant cross sectional aspect ratio but different rates of twist. Correlation with theory was found to be excellent for the chordwise distribution of strain and generally good for the linear relationships linking the deformation with the applied loads. Recommendations were made for areas of further investigation.