Numerical and experimental analysis of struts joined by electromagnetic forming for aircraft applications

Joining by electromagnetic forming can provide high-strength connections of tubes and connector parts from different materials. In order to qualify this technology for manufacturing components made of high-strength aluminum alloys typically used in aircraft manufacturing a parameter study was performed on form fit joining of tubes (outer diameter: 70 mm, wall thickness: 1.6 mm) and mandrels (diameter: 66.6 mm) both made of EN AW-2024 (T351). Since some aircraft applications, e. g. the so-called z-struts, which support the passenger floor of the airplane, are related to high axial compressive loads and medium axial tensile loads, this load scenario was considered. In order to increase especially the compressive load-bearing capacity, joint configurations featuring direct support of the tube end via a step or a shoulder of the joining partner were designed and investigated. The axial support can increase the transferable compressive load, while the tensile load remains largely unaffected. Attention must be paid to the gap between tube end and axial support, which cannot be fully avoided due to axial material flow during the electromagnetic joining process. Bending the tube end into a groove providing axial support of the tube end enables compressive load-bearing capacities, which can approximate the strength of the tube material. Here, increasing bending angles improve the load-bearing capacity under tensile force, but reduce the transferable compressive load. Multiple groove configurations can provide acceptable load bearing capacity considering tensile and compressive load. Numerical simulation can predict the general behavior of components joined by electromagnetic forming, help to understand the damage mechanisms of the joint and allow identifying trends for joint design.