Fatigue data interpretation of 7075-T6 Al sheets by energy density factor in a dual scale model

•The incremental energy density factor ΔS is introduced to the two-parameter fatigue crack growth model.•The proposed model offers a reasonable interpretation on the fatigue crack growth history of 7075-T6 Al sheets•Energy–density-based model can be possibly applied to lower or higher scale ranges.

Fatigue data of 7075-T6 Al sheets has been interpreted by substantial models that can be mostly categorized into stress criterion. It is generally recognized that these models have limitations as well as advantages. Fatigue models can be quite flexible as long as the physical interpretations are reasonable. This paper is started with a formulated fatigue crack growth model that is derived from the concept of strain energy density. Transitional functions as well as mean stress and stress amplitude are incorporated in the fatigue model. Particularly studied is the fatigue crack growth rate of 7075-T6 Al sheets. The curve of crack propagation in the specimen is interpreted by applying the formulated fatigue crack growth model. And a new explanation of the phenomenon is given. The proposed fatigue model can be further extended to multiscale fatigue problems due to the inherent multiscaling property of energy density.