Cyclic crack resistance of aluminum alloys in the crack origin and growth stages

Abstract

of strength and crack resistance, which accordingly determine the load ratio and reliability of increased-survlvability structures. In the case of industrial aluminum alloys an increase in their freedom from the impurities iron and silicon [i], selection of optimum heat treat cycles [2, 3], various methods of production of semifinished products [4, 5], etc. effectively serve this purpose. In selection of materials for increased-survivability structures according to the principle of damage tolerance preference is given to materials with a low crack growth rate and a high fracture toughness in static and cyclic loading, which makes it possible to increase the life and periods of control inspection of parts with cracks. At the same time, for example, for sealed shells, fuel tanks, etc. the life of a part is determined by the period until the origin of a crack, that is, the characteristics of crack resistance in the stages of both crack origin and growth are necessary. However, in the literature there is practically no data on the resistance of materials to crack origin, which is the result of method difficulties [6]. This question becomes even more pressing for the following reason. Certain investigators assume that there is a basic difference between the characteristics of crack resistance of materials in the stages of origin and development of a crack although results obtained recently [7] indicate a direct relationship between them. In this work an investigation was made of the influence of chemical composition (freedom from impurities), heat treat cycles (aging), and preliminary plastic deformation (cold working) on the resistance to fatigue crack origin and development in a number of production aluminum alloys, and the relationship between the characteristics of cyclic crack resistance of materials in these stages of fatigue failure was considered.