The increasing use of composite materials in automobile, aircraft and wind energy applications, together with the need to stress these structures to a higher level increases the demand to assess the fatigue behaviour.
Funding: Bundesministerium für Wirtschaft und Energie im Zentralen Innovationsprogramm Mittelstand (ZIM)
Duration: 2021 – 2023
The "Bionic Walker" project is a cooperation project funded by the Central Innovation Programme for SMEs (Zentrale Innovationsprogramm Mittelstand) for the development and research of a new prosthetic fitting for patients with partial foot amputations. The project consortium includes REHA-OT Lüneburg Melchior & Fittkau GmbH from Lüneburg, Zeisberg Carbon GmbH from Hanover, OK Gummiwerk Otto Körting GmbH from Hameln, the Institute for Orthopaedic Movement Diagnostics (OrthoGO) from Hanover and the institutes belonging to the HPCFK research group, the Institute of Aircraft Design and Lightweight Structures at the Technical University of Braunschweig and the Institute of Polymer Materials and Plastics Engineering at the Technical University of Clausthal. The project consortium is administratively supported by the Wirtschaftsförderungs-GmbH für Stadt und Landkreis Lüneburg.
The task of the new prosthetic fitting is to restore a normal, dynamic and symmetrical gait for patients who have undergone partial foot amputations in order to prevent subsequent complaints caused by changes in gait and to enable them to return more quickly to their everyday social and professional lives. The essential function of the product is achieved by a special spring element made of carbon fibre-reinforced plastic that replicates the characteristics of the anatomical structures that are no longer present. Just like in a healthy musculoskeletal system, part of the kinetic energy is stored in the spring element as potential energy when stepping on during walking. When the foot is lifted again, the compressed spring serves to support the patient and reduces the amount of force required.
Based on a gait analysis to determine the medical requirements, the complete development, production and combination of all components into a demonstrator takes place within the cooperation project. Its functionality and effect will be proven through static and cyclic tests in a testing machine, multi-axis tests with an industrial robot and realistic tests in the gait laboratory.
Funding: DFG
Duration: Since 2019
Team: Tim Luplow , P. Horst, S. Heimbs
The goal of the joint research project DIWA is to investigate the basic causes and effects of structural composite imperfections, such as fiber misalignment, undulation, and residual stress, on the behavior of thick-walled, biaxially braided fiber-reinforced plastic composites under uniaxial and multiaxial quasistatic, cyclic, and thermal loading. The IFL will investigate the fatigue behavior of thick-walled glass fiber composites under uniaxial and multiaxial loading. Experiments will be conducted on samples with thicknesses up to 10 mm to quantify the effect of thickness on mechanical properties and damage phenomena under uniaxial loading. In a next step, box-shaped structures will be tested under multiaxial loading (axial compression and shear) on the MPT (Multiaxial Panel-Test facility). Additionally, a Multi-Scale Model using the finite element method will be developed for the simulation of material properties and damage in thick-walled braided structures. This model will predict the influence of various thickness-dependent parameters such as nesting, roving orientation, and fiber volume fraction. The necessary parameters will be obtained from microscopy, ultrasonic and CT images.
Funding: Deutsche Forschungsgemeinschaft (DFG)
Duration: 2022 – 2025
Team: J. L. Stüven, S. Heimbs
Thermoplastic matrices in fibre composite structures have increasingly become the focus of research in recent years, as they have a decisive advantage over thermoset matrices: their weldability. This offers great potential, e.g. in terms of weight reduction, cycle time reduction and recyclability, which is so important nowadays. Although various welding processes are the subject of research and some of them are already used in industrial applications, the basic operating principle of the processes is very similar. The matrix is melted by applying heat in the area of the intended joining zone. Under the influence of externally applied pressure on the joining partners during cooling, these are then joined to form a component. In our own numerical simulations within the JoinThis project, it has already been shown that residual stresses occur in the joining zone and its surroundings as a result of the cooling process, which cause preliminary damage to the matrix. Particularly for components subjected to cyclic loads, this results in potential pre-damage that reduces the service life and must be taken into account in the dimensioning of components subjected to such loads.
The aim of the FASTHER project is to systematically investigate the damage behaviour of welded thermoplastic fibre composite structures with regard to cyclic loading, taking into account thermal residual stresses. The central research hypothesis is that a procedure for the computational lifetime prediction of welded fibre-reinforced thermoplastics can be created on the basis of the finite element method. With the completion of the project, a detailed modelling of the fatigue damage of welded thermoplastic fibre composite structures is available for the first time, which provides valuable insights with regard to the computational dimensioning in aircraft construction. In addition, the understanding of the numerical modelling of the fatigue of FRP is expanded and a significant contribution is made to the possibilities of experimentally obtaining validation data with the aid of fibre-optic sensors.