Einfluss der thermischen Eigenspannungen auf die statische und zyklische Festigkeit eines Hybridverbunds aus GFK und Stahl

Material compounds are becoming more and more important in the field of lightweight construction. In material compounds, different materials are combined in order to exploit positive synergy effects regarding mechanical properties. To increase the multi-axial strength, fiber-reinforced plastics (FRP) are reinforced with metal in a hybrid composite. These two materials are bonded in a thermally-activated manufacturing process. The different thermal expansion coefficients of the materials and a difference between application and curing temperature result in residual stresses within the hybrid composite. It is assumed that the residual stresses have a negative influence on the component strength.
The hypothetical assumption that there is a negative influence should be verified and quantified. For this purpose, hybrid composites, which have a layered structure of FRP and metal, are examined within this work. Residual stresses act as shear stress in the boundary layer area and as well as normal stresses in the single layers. They are initially determined based on models for different laminate structures. X-ray stress analyses of the metallic components of the hybrid laminate validates the theoretical determination.
The residual stress analysis is followed by the characterization of the shear strength of the boundary layer areas. By using two different test methods, the short bending test and the edge shear test, the influence of the residual shear stresses on the shear strength is analyzed. Furthermore, the influence of the residual stress on the strength of the single layers, especially orthogonal to the fiber direction in the FRP, is shown.
The determined strength values for the boundary layer area and the single layers are finally used to design a component of a hybrid FRP leaf spring. In comparison to a pure FRP leaf spring, the influence of the hybridization and the resulting residual stresses on the strength is analyzed using the example of the hybrid leaf spring. In this context, the guidelines for the design of hybrid composites with respect to the residual stresses are presented.