Mise au point d’un essai de fatigue en flexion pour la caractérisation de matériaux composites

Ecole Centrale de Lyon

Abstract

A new experimental method and testing machine are presented to provide the fatigue behaviour of reinforced plastic materials. The test is conducted on a beam specimen in three point bending fatigue under constant amplitude deflection. The damage is followed by recording, in continuous, the relative load evolution P/P₀ versus the number of cycles N. This typical curve is also used to define the significant damage criterium. An application is treated in E-glass/epoxy, tested in five stress levels (50 to 70% of the ultimate stress). Damage mechanism during fatigue test are observed. For this structure, two phases of damage are pointed out : an initiation mode, and a propagation one, which are well correlated with the evolution curve. At last, it is found that the number of cycles to failure N_R is not really significant for this material. Then, a criterium based on the stiffness decrease is preferable (for instance, N₁₀ characteristic on 10% loss of stiffness).