Analysis of the Fatigue Damage Behavior of AW2099-T83 Al-Li Alloy under Strain-Controlled Fatigue

Muhammed Adinoyi,Jafar Albinmousa,Nesar Merah

doi:10.3221/igf-esis.49.46

Muhammed Adinoyi, Jafar Albinmousa + Show 1 more

Open Access

https://doi.org/10.3221/igf-esis.49.46

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Abstract

Microstructural characteristics, monotonic and strain-controlled cyclic axial behaviors of AW2099-T83 Aluminum-Lithium alloy were investigated. Grain sizes and structures are not uniform in the different orientations studied. High strength and low ductility characterize the tensile behavior of the alloy under static loading. Strain-controlled fatigue testing was conducted at strain amplitudes ranging from 0.3% to 0.7%. Over this range, macro plastic deformation was only observed at 0.7%. Cyclic stress evolution was found to be dependent on both the applied strain amplitude and the number of cycles. Limited strain hardening was observed at low number of cycles, followed by softening, due probably to damage initiation. With low plastic strain, analytical approach was adopted to profile the damaging mechanism for the different applied strain amplitude. Because of the absence of fatigue ductility parameters due to low plasticity, a three-parameter equation was used to correlate fatigue life. Fractured specimens were studied under SEM to characterize the fracture surface and determine the controlling fracture mechanisms. The fractography analysis revealed that fracture at low strain amplitudes was shear controlled while multiple secondary cracks were observed at high strain amplitude. Intergranular failure was found to be the dominant crack propagation mode.

Highlights

L ightweight alloys such as aluminum (Al) alloys are crucial to the transportation sector, especially the aerospace industry
The grains present in the transverse orientation for the investigated aluminum-lithium alloy are a combination of small and large grains, while elongated primary grains with subgrains are present in the extrusion direction
Mean stress evolution for the alloy is generally low and compressive for strain amplitudes lower than 0.7%

Summary

Introduction

L ightweight alloys such as aluminum (Al) alloys are crucial to the transportation sector, especially the aerospace industry. Srivatsan and Coyne [8] studied the cyclic deformation behavior of both Al-Li-Cu and Al-Li-Mn alloys and showed that while the former hardened to failure due to dislocation-precipitates interaction, the latter softened to failure at all strain amplitudes and possessed poor fatigue property. The authors further showed that cracking behavior of the alloy is dependent on applied strain amplitude.

Results

Conclusion