A NEW UNIVERSAL FATIGUE MACHINE FOR PLASTICS AND COMPOSITES

Polymers and composites are more and more involved as structural parts in industry, and so to help the designer we need specific data such a s long term mechanical properties (creep, relaxation, fatigue). In thi s paper we present the fatigue test, by which we study the behavior un der repeated loading. The failure process in fatigue can be always dep icted as a sequence of two steps: (1) Crack initiation (2) Crack propa gation A number of investigations were carried out on the crack propag ation step, ignoring the initiation step, by working on precracked sam ples. This necessitates specialized equipment, methodologies and analy sis. This paper is more devoted to 'endurance behavior', which is the result of the two previous mechanisms (initiation first and then propa gation). After a short presentation of the specific definitions and me ans of fatigue testing, we present a new universal fatigue testing mac hine, on which we can run any kind of test under different conditions (temperature, environment, frequency, stress or strain control, altern ate or ondulate bending, torsion, tensile, etc.).