M atthias Hecht

Abstract

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 D_th = 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.

Session