Characterization of Ultrasonic Welding Bonds in Hybrid Composites – Realisation and Feasibility of a Novel Joining Process in Aerospace Application
Topic(s) : Industrial applications
Co-authors :
Niklas CHALOUPKA (GERMANY), Olivia HELLBACH (GERMANY), Dominik DEDEN , Tobias KARRASCH (GERMANY), Michael KUPKEAbstract :
Carbon fiber reinforced polymers (CFRP) are widely embraced in the aerospace sector due to their advantageous properties at low weight. Composite materials featuring a thermoset matrix exhibit commendable fatigue strength but suffer from inherent brittleness and limited impact toughness. Despite their efficient ease of handling and elevated heat resistance, these materials demonstrate suboptimal damage tolerance. In contradistinction, thermoplastic matrices, characterized by heightened toughness and reduced brittleness, manifest superior impact resilience and damage tolerance. The distinctive melting behaviour of thermoplastics leads to their ability to be remodelled and repaired. However, the need of high temperature and pressures lowers the energy efficiency and increases the cost for thermoplastic composites.
While the aerospace sector generally segregates the use of thermoset and thermoplastic composites, this study aims to reconcile this separation. Specifically, it involves investigations in order to realise the integration of a carbon fiber reinforced thermoset tube with domes composed of CFRP featuring a thermoplastic matrix to form the core structure of a microlauncher's tank. The integration process employs ultrasonic welding, where composite components are fused through frictional heat generated at the boundary surfaces due to ultrasonic vibrations induced by the welding sonotrode.
To validate the viability of ultrasonic welding for joining hybrid materials in an aerospace context, a battery of rigorous tests was undertaken. The investigation involved assessing the compatibility of various thermoset and thermoplastic material combinations, ensuring the formation of a robust interface between the materials. Utilizing polymer foils, the welding process was simulated and tracked through a differential scanning microscopy (DSC) device. Optical confirmation of the interface formation was achieved through microscopic imaging. Welding tests resulted in the identification of suitable process parameters, and shear strengths of the bonding area were assessed to optimize the welding conditions.
Examining the challenges of the ultrasonic welding process, various influencing factors were studied. These included the fiber layup of the tested specimens, the material thickness, and the welding parameters. Furthermore, the impact of a change from room temperature to cryogenic temperatures on the mechanical properties of the welding bond was investigated. A comprehensive exploration of these factors clarified their respective roles in determining the quality of the welding bond. Subsequently, a small-scale demonstrator, featuring a ring-shaped welding line, was constructed to validate and confirm the obtained results. The synthesis of these findings contributes to advancing the understanding of welding dissimilar materials in aerospace applications, paving the way for innovative approaches in composite material integration.
While the aerospace sector generally segregates the use of thermoset and thermoplastic composites, this study aims to reconcile this separation. Specifically, it involves investigations in order to realise the integration of a carbon fiber reinforced thermoset tube with domes composed of CFRP featuring a thermoplastic matrix to form the core structure of a microlauncher's tank. The integration process employs ultrasonic welding, where composite components are fused through frictional heat generated at the boundary surfaces due to ultrasonic vibrations induced by the welding sonotrode.
To validate the viability of ultrasonic welding for joining hybrid materials in an aerospace context, a battery of rigorous tests was undertaken. The investigation involved assessing the compatibility of various thermoset and thermoplastic material combinations, ensuring the formation of a robust interface between the materials. Utilizing polymer foils, the welding process was simulated and tracked through a differential scanning microscopy (DSC) device. Optical confirmation of the interface formation was achieved through microscopic imaging. Welding tests resulted in the identification of suitable process parameters, and shear strengths of the bonding area were assessed to optimize the welding conditions.
Examining the challenges of the ultrasonic welding process, various influencing factors were studied. These included the fiber layup of the tested specimens, the material thickness, and the welding parameters. Furthermore, the impact of a change from room temperature to cryogenic temperatures on the mechanical properties of the welding bond was investigated. A comprehensive exploration of these factors clarified their respective roles in determining the quality of the welding bond. Subsequently, a small-scale demonstrator, featuring a ring-shaped welding line, was constructed to validate and confirm the obtained results. The synthesis of these findings contributes to advancing the understanding of welding dissimilar materials in aerospace applications, paving the way for innovative approaches in composite material integration.