Fatigue strenght of adhesively butt-bonded hollow cylinders under multiaxial loading with constant and variable amplitudes

Adhesive bonding is commonly used in the manufacturing of vehicle bodies. A bond-line has the advantage that the joined flanges are stressed homogenously compared to a conventional spot-welded design. In addition, the bond-line provides a higher stiffness and better damping behavior. There exists still quite some uncertainty in the fatigue assessment of adhesively bonded joints due to a lack of reliable assessment approaches. This is especially true for the case of more complex in-service loading conditions as variable amplitude and multiaxial loading. For example, the experimentally determined actual damage sum in the literature shows a high scatter and is well below the theoretical value of one proposed by Palmgren-Miner. This uncertainty is typically countered by an over-dimensioning of the bond. In order to identify the fatigue strength behavior under constant and variable, multiaxial loading, fatigue tests on adhesively butt-bonded double hollow cylinder specimens with a thickness of the bonding of 0.3 mm have been performed under load control. The endurable damage sums according to the Palmgren-Miner hypothesis with a modified slope after the knee point of the Woehler line are determined and compared to data from the literature, they are significantly lower than Dth = 1. Non-proportional multiaxial loading (ϕ = 90°) does not reduce the fatigue life compared to proportional (ϕ = 0°).