Within this paper in the First Part there are presented some general considerations upon the assessment mode of durability at variable loads. There are analyzed those three design philosophies, respectively: the safe- life, infinite life; safe-life, finite life and damage tolerant. In this context there are then exposed the impact fatigue characteristics as well as the durability assessment parameters at such tests. In the Secon Part the authors present some results obtained in the Impact Fatigue Laboratory of the Politehnica University of Timisoara regarding the durability at impact fatigue.