The influence of a tension load on laminates under torsion

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The influence of a tension load on laminates under torsion

Sen, J.K.

In expanding the study 'fracture of glass-epoxy laminates under torsion and combined tension-torsion loads', composite materials: fatigue and fracture (fifth volume) ASTM STP 1230, 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 systems, were tested under torsion and combined tension-torsion. The laminate configurations consisted of 30 deg of angle, 45 deg of angle or 60 deg of angle plies located between 0 deg of angle sublaminates. All failures initiated with through-the-thickness shear cracks at the free edge, followed by delaminations. Superposing a tension load increased both the torsional load required to twist to a given angle and the torsional load to failure. An increase in the torsional load for a given twist increases the control loads to the helicopter rotor system. A tension load on the rotor system, represented by the centrifugal force, increases significantly the effective rigidity of the system, and hence the magnitudes of the control loads. The laminates are compared to determine their design efficiencies with respect to the control loads.