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Fractal interface design for defined adjustment of the interlaminar strength of metal-thermoplastic-composites

Subject Area Coating and Surface Technology
Metal-Cutting and Abrasive Manufacturing Engineering
Term from 2021 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 494736555
 
Final Report Year 2025

Final Report Abstract

Lightweight design plays a key role in achieving global goals such as reducing fossil fuel consumption and greenhouse gas emissions. The substitution of metal components with metalpolymer composites entails a reduction in mass. Thermoset composites are already well established in the aerospace sector. However, the high manufacturing costs are an obstacle to a wider range of applications. Substitution with thermoplastics is one solution. The resulting composite strength is based on mechanical interlocking and combines form-fit, material-fit and force-fit components. In particular, targeted processing or microstructuring of the metallic composite partner can increase composite strength and extend the range of applications. The aim of the project was the development of algorithms for the evaluation of predefined surface microstructures based on fractal geometry. Furthermore, the correlations between the fractal geometry and the interlaminar strength, considering surface and interfacial chemical properties, should be determined. Surface conditioning at different scaling levels and modification with adhesion-promoting organosilanes are used to identify the ranges of validity of the assumptions made. In order to increase the joint strength, a process with geometrically determined cutting edges for the defined adjustment of the surface microstructure based on fractal geometry is developed. In this project, laser processing is initially used to create defined surface microstructures. Specimens processed in this way are used, among other things, to determine the measurement conditions for recording the geometric properties of the microstructures in order to subsequently determine the fractal dimension. Similar specimens are also used for organosilane coating. Shear strength tests demonstrate an increase in bond strength with higher microstructure density and a further increase with organosilane coating. Ultrasonic vibration assisted deformational machining (UVADM) is developed to microstructure the metallic joining partner. Tool geometry and relevant ranges of machining parameters are designed based on FE simulations. The influences of tool geometry and the machining conditions on the surface properties are determined in the experimental investigations. The analyses show a high degree of agreement with the simulations. Correlations between surface microstructure and strength of the compound were determined. The fractal dimension is shown to be a suitable means of evaluating the relationships quantitatively.

Link to the final report

https://doi.org/10.34657/19377

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