Bayreuth design light composites by combining compression

Classical mechanical testing of fibre reinforced composites often cannot answer important questions like “When do first subcritical damages occur?”, “Which microscopic damage mechanisms are acting at particular load levels?” and “What is the contribution of the individual components of the composite to the damage evolution?”

In order to better understand the micromechanic mechanisms involved in the failure of polymer composites the long-known method of acoustic emission analysis is combined in a novel manner with the mechanical testing of composite materials. Thus, a profound understanding of their complex failure mechanisms has been generated, going far beyond the current state of the art.

Acoustic signals emitted from the sample during testing are analysed and classified by means of pattern recognition techniques. Based on the frequency composition of acoustic signals, different damage mechanisms as matrix cracking, interface failure and fibre breakage are distinguishable. Thus, it is possible to identify ocurrent damage mechanisms and their load-dependent course before final failure of the composite.

As second step the developed methodology was transferred to dynamic testing in order to represent realistic long-term loading conditions. Microscopic damage progress was correlated with the energy dissipated within the material during cyclic loading. This allows a fine-differentiated analysis of the contribution of different damage mechanisms to composite material’s fatigue at various load levels.

In particular for the design of highly dynamic loaded parts it is necessary to understand the microscopic failure mechanisms contributing to their long-term fatigue behaviour. Only with this knowledge it is possible to take full advantage of the lightweight-design-potential of composite materials.

Composite Europe