Increasing the fatigue strength of composites | NewsLIGHT #18 | SLA

Hybridization offers opportunities to increase the fatigue strength of composite materials

Composites are attracting an increasing popularity as a spring material, in particular the market for glass-fibre reinforced plastic (GFRP) springs is growing at an ever-increasing rate. However, the use of GFRP as a spring material is also accompanied by high dynamic loads, which puts the fatigue strength of the material in the focus of the component design. In general, GFRPs have a very good fatigue strength, but due to the complex design and calculation of fatigue strength properties, components are overdimensioned to provide the necessary safety against fatigue failure. By increasing the fatigue strength, components can be made lighter or more durable.

Fatigue fractures are the result of many individual failures in the microstructure, which further develops into macroscopic fracture clusters. In particular, the growth of microfractures into fracture clusters can be prevented by hybridization. Hybridization of composites is characterized by the use of different fiber materials within one component. The approach is already widely used for composite applications which require high impact strength. However, the use of composite hybridization to increase the fatigue strength is still largely unexplored.

AZL Partner IPTE

© SLA | Conveyor machine with GFRP leaf springs 

Within the recently started research project DurableHybrid it is investigated how the fatigue strength of composites can be increased by the use of hybrid reinforcement textiles. The focus is on GFRP leaf springs that are used in a wide variety of vibrating machines, such as feeding machines and screening machines. This results in a very high dynamic load on the springs, which ultimately limits their service life. An increase in the fatigue strength of the spring material directly extends the service life of the GFRP leaf springs.

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© SLA | Fracture development in ordinary composites

In order to increase the fatigue strength, crack arresting fibers are integrated into textiles within the framework of the project. The crack arresting fibers used are characterized by high elongation at break and high fracture toughness. The hybrid reinforcement textiles are further processed into prepregs, from which specimens and demonstrators are manufactured. The development is accompanied by extensive fatigue tests. The material properties obtained in this way are then used to develop a model for the design of hybrid composites.

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© SLA | Fracture arresting in hybrid composites 

The companies involved are: P. J. Prause Durotec GmbH; C. Cramer Weberei, GmbH & Co.KG; Krempel GmbH as well as the Institut für Textiltechnik of RWTH Aachen University and the Institute of Structural Mechanics and Lightweight Design of RWTH Aachen University. The project is funded by the German Federal Ministry for Economic Affairs and Energy as part of the “Technologietransfer-Programm Leichtbau”