Analysis of Tubular Adhesive Joints in Aluminum and Composite Structures under Crush and Tensile Loads

Abstract

As the automotive industry moves toward developing lightweight crashworthy structures, it is expected that a multi-material solution involving steels, aluminum alloys and high-performance composites will become increasingly common in future vehicles. Joining a variety of materials with different physical, mechanical, and thermal characteristics is one of the major challenges for such multi-material designs. Adhesive joining is emerging as one of the key joining methods in multi-material structures, since in general, adhesives are compatible with most materials under consideration for lightweight vehicles. There are many body, chassis and powertrain components in vehicles that are designed with tubular sections. A few examples of these components are the front rails, underbody frames or sub-frames, instrument panel crossbeams, drive shafts and spaceframe structures. Increasing use of hydroforming and closed-section extrusions will lead to even more use of tubular sections, especially in crush-resistant components, such as front rails and roof rails. Tubular joints are also used in buses and other heavy vehicle constructions. Unlike the seam adhesive joints between thin sheets or panels, there has not been much research and design studies on tubular adhesive joints in which a tube is fitted in another tube of the same material or different materials. In a crash condition, tubular structures are designed to crush in a controlled manner. In addition to the crush mode, crush energy absorption and peak crush load are the two most critical parameters to consider for improved crashworthiness. If the tubular structure is made of adhesive joints, it is important that the joint failure does not occur before controlled crushing of the joined tubes. The crush characteristics are affected by joint geometry and material properties. Hence, the key objective of this research is to develop a crush resistant tubular adhesive joint in aluminum-aluminum, composite-composite, and composite-aluminum structures using finite element analysis. A Design of Experiments approach is used to understand the interactions between different joint parameters and their effects. Since such tubular structures are likely to be subjected to different forms of loading, the dissertation aims to present optimal tubular adhesive lap joint design choices for maximum energy absorption under crush load and joint failure strength under tensile load using finite element analysis.