Analysis and testing of adhesively bonded lap joints Page: 1 of 10
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ANALYSIS AND TESTING OF ADHESIVELY BONDED LAP JOINTS
K. E. Metzinger and T. R. Guess RECEIVED
Sandia National Laboratories CEI E1995
Albuquerque, New Mexico T
ABSTRACT
Detailed studies of adhesively bonded tubular lap joints subjected to axial loads can be efficiently
performed with two-dimensional (2D) finite element analyses. However, three-dimensional (3D)
analyses are required to model the bending of tubes and the axial loading of many other shapes -
such as airfoils. Unfortunately, these 3D analyses require significantly more time and computer
resources than 2D analyses. Thus, it is of interest to determine whether some aspects of 3D
behavior can be captured with 2D analyses. A series of finite element analyses will show that the
shear stress in the adhesive of a tubular or an elliptic lap joint - due to a bending load - can be
reasonably estimated with a 2D analysis even though the behavior is 3D. After the agreement
between 2D and 3D analyses is detailed, preliminary efforts to assess the importance of adhesive
geometry at the end of the bond will be discussed. Experimental measurements of the mechanical
properties of a structural adhesive used in joint tests will also be presented. Tension, compression,
and stress relaxation data for a filled, amine-cured epoxy adhesive will be discussed.
INTRODUCTION
Adhesively bonded lap joints are increasingly being used in wind turbine joints as blade
attachments. Consequently, numerous axisymmetric finite element analyses have been performed
in conjunction with the testing of tubular joints. While two-dimensional (2D) analyses can
accurately represent tubes subjected to axial loads, three-dimensional (3D) analyses are required to
model the bending of tubes. 3D analyses are also required to model the axial loading or bending of
many other shapes - such as airfoils. Unfortunately, 3D analyses typically require much more time
and computer resources than 2D analyses, making parametric studies impractical. However, some
aspects of 3D behavior can be estimated with 2D analyses. This study will compare the shear stress
in the adhesive of a 2D axially loaded steel-to-composite tubular lap joint with the shear stresses in
the adhesives of the corresponding 3D tubular joint and a similar elliptic joint subjected to bending.
After the correlation between 2D and 3D analyses has been discussed, the issue of the adhesive
geometry at the end of the bond will be addressed. The details of the adhesive geometry are of
interest for two reasons. First, it is important to know if the truncated adhesive geometry typically
used in finite element analyses predicts results similar to those obtained for more realistic
geometries. Second, it would be of general interest if a particular adhesive geometry produces
lower stresses in the adhesive or the adherend. In this paper, the effect of three different adhesive
geometries on the adhesive and the composite adherend will be considered.
Finally, some experimental measurements of the mechanical properties of a structural adhesive
used in joint tests will be presented. A thorough characterization of the adhesive material properties
will facilitate the correlation of analyses with destructive joint tests. Tension compression, and
stress relaxation data for an epoxy adhesive will be discussed.
FINITE ELEMENT ANALYSES
1. Two-Dimensional
The first step in this study was to establish that the shear stress in a linear elastic adhesive bond can
be accurately determined by using a relatively coarse finite element mesh. Figure 1 shows the fairly
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Metzinger, K.E. & Guess, T.R. Analysis and testing of adhesively bonded lap joints, article, October 1, 1995; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc621517/m1/1/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.