Endless Fibre Reinforced Composite-Metal-Impeller: High Speed Burst Testing -Damage and Failure Analysis
A1 Materials & Wear Resistance
The performance and efficiency of future and existing blowers can be increased by using new types of high-performance impellers made of fibre reinforced materials. Such composite materials have outstanding density related mechanical properties, which allow the speed to be increased significantly. As a result of the reduced mass such impellers, in particular the reduced inertia, the impellers can react faster to variable speeds and consume less energy. Composites allow a variable design of the blades. This allows flow-optimised cross-sections to be realised, which in addition to higher efficiency also has the potential to reduce noise. Furthermore, the layered design of such impellers can be used to integrate sensors as a basis for component monitoring and data generation.
Due to the special characteristics of fibre composite materials with their large number of adjustable parameters and the special knowledge required for this in combination with high expenditures and risks for the development and production of integral rotors, these are currently only niche products.
At the TU Dresden, in cooperation with the Forschungsvereinigung für Luft- und Trocknungstechnik (FLT), a modular design of a high-performance impeller was developed, for which the functionality was presented in a first FAN paper. Compared to the integral solutions, the manufacturing effort of this modular design is greatly reduced, which allows a higher availability and variability in production. In addition to the design, a numerical-based methodology for mechanical design was elaborated and presented. This allows the consideration of material-specific damage and failure behaviour. Based on this virtual component development, speeds of about 7,500 rpm were already achieved in the first test, which corresponds to a circumferential speed of about 400 m/s and thus corresponds to a speed increase of about 30% compared to the metallic variant.
In this paper, results of the spin test up to failure at up to 538 m/s are presented. Based on high speed images taken during the spin test and fracture analysis, it is possible to interpret the damage and failure behaviour of the structure and compare the results of the simulation. A focus of the discussion is on the selected joining technique in relation to the bursting speed and an analysis of varying bursting speeds. This results in measures and indications for the further improvement of the design and for the further increase of the performance and reliability of such structures.
The smaller and lighter fragments resulting from the bursting are then considered in the discussion of the safety-related advantages of the overall system. The results of this simplified feasibility study show a clear potential for increasing the speed of high-performance radial fans in metal-fibre composite design compared to metal impellers.
Keywords: composite material, radial fan, hybrid design, high speed burst test, failure analysis