THE EFFECT OF A SUPERIMPOSED MEAN STRAIN ON THE FATIGUE BEHAVIOR OF THE ALUMINUM-ALLOY ALMG5MN

The cyclic stress-strain response of the aluminum alloy AlMg5Mn in thr ee different strength conditions is studied with emphasis on the influ ence of a superimposed mean strain and mean stress, respectively. The cyclic deformation behavior is characterized by a pronounced cyclic sa turation independent of the prior heat treatment. Decreasing strength of the material is connected with a increasing extent of mean stress r elaxation and cyclic creep, respectively. However, these transient eff ects are mainly restricted to the initial stage of cyclic life. In ord er to validate the lifetime data observed, a comparison with data from the literature is performed. For this purpose, it is necessary to app ly a damage parameter which takes the damaging effect of a mean stress into account, since the cyclic lifetime values reported have mostly b een obtained in rests without mean stress or mean strain. It is found that the damage parameter P-SWT after Smith, Watson and Topper is suit able for the two conditions with higher strength. In the case of the s oft condition, the damage caused by plastic mean strain is underestima ted. As a consequence the cyclic lifes observed lie at the lower bound ary of the scatter band of the literature data.