Matthias Hecht is a research associate at the Technical University of Darmstadt. He is working on the estimation of the fatigue life of bonded joints. The core topics are variable amplitude loading and multiaxial loading with and without phase shifts.
Adhesive bonding is a frequently used joining technology in the manufacturing of vehicle bodies. In comparison to conventional spot-welded designs, adhesive bonding provides a higher stiffness due to a planar load transfer. Furthermore, there are advantages in damping behavior and chemical separation in multi-material designs.
Up to now, 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 Dth = 1 proposed by Palmgren-Miner. This uncertainty is typically countered by an over-dimensioning of the bond.
In order to increase the accuracy of fatigue methods for vehicle bodies, tests were carried out on component-like specimens, so called “bowl specimens”. These specimens consist of a deep drawn sheet that is bonded with a thermosetting structural adhesive to a planar sheet and are subjected under cyclic loading. They were loaded uniaxially and multiaxially, with (φ = 90°) and without phase shift (φ = 0°). Even uniaxial loading results in multiaxial stress due to the complexity of the geometry.
A comparison is made between the actual damage sums according to Palmgren-Miner of homogeneously butt-bonded hollow cylinders (presented at the Fatigue Design 2021) and these complex bowl specimens. Additionally, a difference in the influence of the phase shift on the fatigue behavior of these two specimen types is shown.
|Room 9||Thursday 30th November||10:45-11:15||Matthias Hecht|
S09-4 Fatigue of assemblies
70 - Fatigue strength of adhesively bonded deep drawn sheet specimens under multiaxial loading with variable amplitudes