Multiaxial fatigue of cast aluminium EN AC-42000 T6 (G-AlSi7Mg0.3 T6) for automotive safety components under constant and variable amplitude loading

Regarding the fatigue behaviour of EN AC-42000 T6 (A 356 T6), which is the most frequently used cast aluminium alloy for automotive safety components, especially under non-proportional constant and variable normal and shear stress amplitudes with changing principal stress directions, a poor level of knowledge was available. The reported investigations show that, under non-proportional normal and shear stresses, fatigue life is increased in contrast to ductile steels where life is reduced due to changing principal stress directions. This behaviour caused by the low ductility of this alloy (e < 10%) compared to quenched and tempered steels suggests the application of the Normal (Principal) Stress Hypothesis (NSH). For all of the investigated stress states under multiaxial constant and variable (Gaussian spectrum) amplitudes without and with mean stresses, the NSH was able to depict the life increase by the non-proportionality and delivered, for most cases, conservative but non-exaggerated results

Multiaxial Fatigue Assessment of Friction Stir Welded Tubular Joints of Al 6082-T6

The present paper addresses the problem of designing aluminium friction stir (FS) welded joints against multiaxial fatigue. After developing a bespoke FS welding technology suitable for joining aluminium tubes, some one hundred welded tubular specimens of Al 6082-T6 were tested under pure axial, pure torsional and biaxial tension-torsion loading. The influence was explored of two independent variables, namely the proportional or nonproportional nature of the biaxial loading and the effect of axial and torsional non-zero mean stresses. The experimental results were re-analysed using the Modified Wöhler Curve Method (MWCM), with this bi-parametrical critical plane approach being applied in terms of nominal stresses, notch stresses, and also the Point Method. The validation exercise carried out using these experimental data demonstrated that the MWCM is applicable to prediction of the fatigue lives for these FS welded joints, with its use resulting in life estimates that fall within the uniaxial and torsional calibration scatter bands. The approach proposed in the present paper offers, for the first time, a complete solution to the problem of designing tubular FS welded joints against multiaxial fatigue loading

Hybrid design concept using high-strength cast steel inserts for tubular joints of offshore structures

The use of hybrid nodes combining high-strength steels with cast steel inserts of same quality meets the requirements of higher fatigue life and strength compared to conventionally welded nodes and opens up the possibility for offshore construcitons for greater water depths than up to now