INFLUENCE OF THE PREVIOUS STRAIN LEVEL IN THE FATIGUE BEHAVIOUR OF DUCTILE STEEL FOR DEEP DRAWING

摘要

In the current work, the influence of the initial and medium strain under which fatigue tests are performed in the fatigue behaviour of two different steels for deep drawing is analysed. The two steels analysed has the commercial denomination DC05 (according to DIN EN 10130) and ZStE260 (DIN EN 10268). In both cases, the expressions proposed by Ramberg-Osgood (1) for the cyclic stress-strain curve (σ-ε) as well as those proposed by Basquin (2) and Manson-Coffin (3),(4) for the relationship between strain amplitudes and life (ε-N curve) are assumed as valid. The fatigue characterisation of both materials is made according to standard laboratory procedures, previously developed and setting up in the Instituto Tecnol6gico de Arag6n ((5) and (6)), using for that as basis the recommendations proposed by ASTM ((7), (8) and (9)). The most usual problems found during the tests have been associated to buckling in the specimens under compression loads. Those problems, due to the geometry of the specimens tested (small thickness, about 1.5 mm.), have been solved by using several experimental techniques and by manufacturing specific tests tooling (as is described in (10)).