When the test has started for a fixed o value of the stress, the moment at which the regulation of elongat­ion starts to act is not always defined precisely; the loading conditions: speed of rise under constant load, loading in stages with waiting periods, constant speed of elongation. ###>­ les conditions de mise en charge : vitesse de montée en charge constante, chargement par paliers avec périodes d'attente, vitesse d'allongement constante.