Ultrasonic joining of through-the-thickness reinforced metal-composite hybrid structures

Verbindungskonzepte, die traditionell für den Verbinden von Metall-Verbundstoff-Strukturen verwendet werden, weisen mehrere Beschränkungen in Bezug auf den Lasttransfer zwischen den Materialien. Die vorliegende Doktorarbeit zielt auf die Einführung von Ultrasonic Joining (U-Joining) ab, einem neuen Fügeverfahren zur Herstellung von throught-the-thickness verstärkten Hybridverbindungen aus Metall und Faserverbundwerkstoff mit verbesserter out-of-plane Festigkeit. Um die Machbarkeit des Fügeprozesses zu demonstrieren und die Korrelation zwischen Prozess- und Fügeeigenschaften zu beschreiben, wurde ein Fallstudienansatz gewählt, der kommerziell erhältliches glasfaserverstärktes Polyetherimid und MIM-Structured Ti-6Al-4V verwendet.Joining concepts that are traditionally used to join hybrid metal-composite structures present several limitations with regard to load transfer between the materials. The present doctoral thesis aims at introducing the Ultrasonic Joining (U-Joining), a new joining approach to produce through-the-thickness reinforced metal-composite hybrid joints that have improved out-of-plane strength. In order to demonstrate the process feasibility and describe the correlation between process and joint properties, a case study approach was chosen, using commercially available glass-fiber reinforced polyetherimide and MIM-Structured Ti-6Al-4V

Hysteresis analysis and control of a metal-polymer hybrid soft actuator

The number of applications of stimulus-responsive polymers is growing at an impressive rate. The motivation of this contribution is to use a commercially available low-budget silver-coated polyamide (PA6) as a thermo-responsive metal-polymer hybrid soft actuator. Polyamide is a hygroscopic polymer; therefore, its mechanical and physical-chemical properties are affected by exposition to humidity or immersion in water. The effect of water absorption content on the PA6 and silver-coated PA6 monofilament properties, such as mass change and resistance, were evaluated. Moreover, the influence of swelling and shrinking effects on the surface morphology, caused by variations of moisture and water immersion, was investigated. Based on these variations, the dynamics of the resistance of the hybrid material were analyzed in the context of the proposed hysteresis model. An identification procedure of the hysteresis is presented along with an approximation of the upper and lower bound based on a constrained least square approach. A switching logic algorithm for this hybrid dynamic system is introduced, which makes it possible to structure the non-linear function in a switching mode. Finally, a non-linear integral sliding manifold is proposed and tested to control the resulting force of the actuator.hysteresis model. An identification procedure of the hysteresis is presented along with an approximation of the upper and lower bound based on a constrained least square approach. A switching logic algorithm for this hybrid dynamic system is introduced, which makes it possible to structure the non-linear function in a switching mode. Finally, a non-linear integral sliding manifold is proposed and tested to control the resulting force of the actuator.Helmholtz Associatio

LaCrO3 composite coatings for AISI 444 stainless steel solid oxide fuel cell interconnects

Doped lanthanum chromite-based ceramics are the most widely used interconnector material in solid fuel cells (SOFC) since they exhibit significant electrical and thermal conductivity, substantial corrosion resistance and adequate mechanical strength at ambient and high temperatures. The disadvantage of this material is its high cost and poor ductility. The aim of this study is to determine the mechanical and oxidation behavior of a stainless steel (AISI 444) with a LaCrO3 deposition on its surface obtained through spray pyrolisis. Coated and pure AISI 444 materials were characterized by mechanical properties, oxidation behavior, X-ray diffraction and scanning electronic microscopy. Results indicated that the coated material displays better oxidation behavior in comparison to pure stainless steel, but no improvement in mechanical strength. Both materials indicate that deformation behavior depends on testing temperatures