In the HIGH-T research project, which was recently approved by the German Research Foundation, the Institute of Production Engineering and Machine Tools (IFW) at Leibniz University Hannover and the Institute of Aircraft Design and Lightweight Structures (IFL) at the Technical University of Braunschweig are working together on the development of a novel, hybrid high-performance joining concept and the associated process chain in order to significantly improve the structural integrity and damage tolerance of T-joints in thermoplastic carbon-fiber reinforced composite structures.
Such joints represent a critical weak point in lightweight structures, especially under impact loads. Reinforcement with form-fitting metallic elements is a proven principle that is already being used successfully in thermoset systems to increase energy absorption and prevent brittle failure. However, the transfer of this concept to thermoplastic laminates has so far failed due to a fundamental problem: the subsequent introduction of any z-reinforcement into the consolidated thermoplastic material inevitably leads to fiber and matrix damage, which compromises structural integrity.
This is where the project comes in with an innovative, interdisciplinary approach that closely integrates manufacturing technology and structural mechanics. At the heart of the project is a two-stage process chain that enables the completely damage-free integration of metallic reinforcement pins. To this end, the Thermoplastic Automated Fiber Placement (TAFP) process controls the formation of defined gaps between the fiber tapes by means of a targeted, local reduction of the consolidation energy. These gaps form a precise channel pattern that serves as a guide for the subsequent, force-free positioning of the pins. In a second step, the composite is finally consolidated. During this process, the thermoplastic matrix melts, infiltrates the undercuts of the pins, and, after solidification, creates a high-strength mechanical interlock. This form fit results in load transfer that is primarily based on mechanical locking rather than pure adhesion.
In order to unlock the full potential of this technology, the project is pursuing two equally important main objectives. The IFW is researching the manufacturing fundamentals. Here, the interactions between TAFP process parameters, the resulting laminate morphology, and the flow behavior of the matrix are being investigated in order to ensure reliable production of the optimized composite. At the same time, the IFL is focusing on structural mechanical design and optimization. Using advanced, validated simulation methods, the complex failure behavior is analyzed in order to iteratively design the pin geometry and arrangement for maximum peel resistance and energy absorption.
The success of the project will be validated by demonstrating the superior performance of the hybrid joint concept compared to the state of the art (purely welded joint) in a final comparative impact test campaign.
Contact:
For further information, please contact Dr.-Ing. Carsten Schmidt on +49 4141 77638 11 or by e-mail at schmidtc@ifw.uni-hannover.de.
