Investigation of laser heating as a method for fatigue crack growth retardation in aluminum alloy 2198-T851

Abstract

The growing demand for lighter structures and for the lowering of production and operation costs stimulates research in materials and processes for aircraft industry. Aluminum alloys are still the main materials employed in aircraft mainframes and fuselage skin, representing about 60% of the structure. The modern trend is to design and build hybrid structures, combining composite materials and advanced aluminum alloys. It is possible to adopt less conservative calculations for damage tolerant metallic structures by enhancing the reliability of the remaining life predictions of cracked components. New methods promoting fatigue crack growth retardation by the introduction of residual stresses, like the laser heating, are promising tools to improve the damage tolerance. Even if the positive effects of the induced residual stresses are not taken in account in project, manufacturers and operators use such techniques because they help reducing the maintenance costs. The aim of this project is to find the best parameters and strategy for the production of laser heating lines in 2198-T851 alloy sheets with 2.0 mm in thickness, in order to reduce the fatigue crack growth rate in this material. Laboratory tests using M(T) specimens under several loading conditions will provide a unique dataset on the laser heated material. Mathematical models from literature will be tested and compared as for their ability in describing the effect of laser heating on fatigue crack growth behavior of the alloy. Moreover, the residual life and inspection intervals of some typical aircraft applications will be predicted by using numerical integration. (AU)