HIGH-T – High-performance hybrid joining concept for thermoplastic composite T-joints: Enhanced manufacturing and simulative methods for superior structural integrity

• Applicants: Professor Dr.-Ing. Berend Denkena; Professor Dr.-Ing. Sebastian Heimbs
• Subject Area: Plastics Engineering ; Lightweight Construction, Textile Technology ; Production Automation and Assembly Technology
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 576361611

The central objective of the research project HIGH-T is to develop a novel, hybrid high-performance joining concept to decisively improve the structural integrity and damage tolerance of T-joints in thermoplastic fiber-reinforced composite structures. Such joints represent a critical vulnerability in lightweight structures, particularly under impact loading. Reinforcement through interlocking metallic elements is a proven principle that has already been successfully used 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 insertion 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 begins with an innovative, interdisciplinary approach that closely integrates manufacturing technology and structural mechanics. The core of the project is a two-stage process chain that enables the completely damage-free integration of metallic reinforcement pins. In this process, the Thermoplastic Automated Fiber Placement (TAFP) process is used to control the creation of defined gaps between the fiber tapes through a targeted, local reduction of 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 consolidated. During this stage, the thermoplastic matrix melts, infiltrates the undercuts of the pins, and, upon solidification, creates a high-strength mechanical bond. This form-fit results in a load transfer that is based primarily on mechanical locking rather than on pure adhesion. To unlock the full potential of this technology, the project pursues two co-equal primary objectives. The Institute of Aircraft Design and Lightweight Structures (IFL) focuses on the structural-mechanical design and optimization of the joint. Using advanced, validated simulation methods, the complex failure behavior is analyzed to iteratively design the pin geometry and arrangement for maximum delamination resistance and energy absorption. In parallel, the Institute of Manufacturing Technology and Machine Tools (IFW) investigates the manufacturing-related fundamentals. Here, the interactions between TAFP process parameters, the resulting laminate morphology, and the flow behavior of the matrix are examined to ensure a reliable manufacturing process for the optimized joint. The success of the project will be validated by demonstrating the superior performance of the hybrid joining concept compared to the state of the art (a purely welded joint) in a final, comparative impact test campaign.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Carsten Schmidt