Investigation on rotational bending fatigue behaviour of 6061-T4 aluminium alloy tube joining components

The rotational bending fatigue behaviour of 6061-T4 aluminium alloy tube joining components (TJCs) was investigated by experiments and numerical simulations. The main findings include: 1) The load distribution characteristics of TJCs during the fatigue tests revealed that stress fatigue predominates when the deflection is below 1.8 mm, and strain fatigue becomes the dominant failure mode when the deflection exceeds 1.8 mm. 2) Rotating bending fatigue under pulsating pressure involves multiaxial fatigue driven by circumferential pulsating stress, axial variable-amplitude cyclic stress, and torsional constant-amplitude stress. Bending stress has significantly higher maximum and minimum values than torsional stress, indicating that bending loading dominates the fatigue failure of TJCs in actual tests. 3) Fatigue cracks initially originate at stress concentration points on the outer side of the tube wall and propagate from the outer side to the inner side of tube wall, ultimately resulting in fatigue failure. 4) As deflection increases, the maximum and minimum cyclic stresses under combined bending and torsional loading gradually increase, resulting in a higher stress amplitude that significantly reduces fatigue life. The rise in stress amplitude is the dominant factor responsible for this reduction.