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. 2023 Feb 14;16(4):1595.
doi: 10.3390/ma16041595.

Prediction of Fatigue Crack Initiation of 7075 Aluminum Alloy by Crystal Plasticity Simulation

Takayuki Shiraiwa  1 , Fabien Briffod  1 , Manabu Enoki  1
Affiliations

Prediction of Fatigue Crack Initiation of 7075 Aluminum Alloy by Crystal Plasticity Simulation

Takayuki Shiraiwa et al. Materials (Basel). .

Abstract

The 7075 aluminum alloy is a promising material for the aerospace industry due to its combination of light weight and high strength. This study proposed a method for predicting fatigue crack initiation of the 7075 aluminum alloy by crystal plasticity finite element analysis considering microstructures. In order to accurately predict the total fatigue life, it is necessary to calculate the number of cycles for fatigue crack initiation, small crack growth, and long crack growth. The long crack growth life can be estimated by the Paris law, but fatigue crack initiation and small crack growth are sensitive to the microstructures and have been difficult to predict. In this work, the microstructure of 7075 aluminum alloy was reconstructed based on experimental observations in the literature and crystal plasticity simulations were performed to calculate the elasto-plastic deformation behavior in the reconstructed polycrystalline model under cyclic deformation. The calculated local plastic strain was introduced into the crack initiation criterion (Tanaka and Mura, 1981) to predict fatigue crack initiation life. The predicted crack initiation life and crack morphology were in good agreement with the experimental results, indicating that the proposed method is effective in predicting fatigue crack initiation in aluminum alloys. From the obtained results, future issues regarding the prediction of fatigue crack initiation were discussed.

Keywords: aluminum alloy; crack initiation; crystal plasticity; fatigue; finite element method.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Inverse pole figure map of 7075 aluminum alloy in the TD-RD plane (reprinted with permission from Ref. [18]), (b) finite element model of polycrystalline aggregate and boundary conditions.
Figure 2
Figure 2
(a) Schematic of a potential crack path defined as the intersection of the slip plane and the 2D finite element model. (b) An example of the potential crack paths for a single crystalline grain. The path with the highest fatigue indicator parameter (FIP) is highlighted with a bold line.
Figure 3
Figure 3
(a) First ten hysteresis loops obtained from low-cycle fatigue experiments performed in the rolling direction (reprinted with permission from Ref. [18]), (b) calibrated stress-strain hysteresis loops in low-cycle fatigue simulations.
Figure 4
Figure 4
(a) Mises stress distribution at maximum stress applied (σmax = 340 MPa, R = −1). (b) Macroscopic stress-strain curve. (c) Stress-strain curves at the higher and lower stress locations indicated by arrows in (a).
Figure 5
Figure 5
Distribution of cumulative plastic shear strain for 12 slip systems in the last calculation step (σmax = 340 MPa, R = −1). The predicted crack initiation site is indicated by an arrow and a red solid line.
Figure 6
Figure 6
Predicted fatigue crack initiation life and experimental fatigue crack initiation and failure life taken from the literature [5].
See this image and copyright information in PMC

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