Fatigue damage initiation of a PA66/glass fiber composite material is studied with interrupted tests carried out with an “alternative bending device” and a small applied strain. During the damage initiation period, no change of macroscopic properties, density, cristallinity ratio, glass transition temperature, and flexural elastic modulus is observed. Polysequential tests are carried out with three rest times differing by their length. These rest times allow the relaxation of macromolecular chains in the region of the microdefects and increase the number of cycles at fracture. The most efficient stop is the one just before the final fracture. The comparison of the fatigue behavior of the composite and its neat matrix shows that the microdefects relaxed during the break are identical to those which initiate damage and final fracture.
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