THE INFLUENCE OF A TENSION LOAD ON LAMINATES UNDER TORSION

The influence of a tension load on the behavior of laminates subjected to torsion was evaluated through test and analysis, Nine different 32 -ply glass-epoxy laminates, typical of flexbeams in helicopter rotor s ystems, were tested under torsion and combined tension-torsion. The la minate configurations consisted of 30 degrees, 45 degrees or 60 degree s plies located between 0 degrees sublaminates, All failures initiated with through-the-thickuess shear cracks at the free edge, followed by delaminations. Superposing a tension load increased both the torsiona l load required to twist to a given angle and the torsional load to fa ilure, An increase in the torsional load for a given twist increases t he control loads to the helicopter rotor system, A tension load on the rotor system, represented by the centrifugal force, increases signifi cantly the effective rigidity of the system, and hence the magnitudes of the control loads, The laminates are compared to determine their de sign efficiencies with respect to the control loads.