Definition of requirements for reference experiments to determine and evaluate various damage mechanisms in fibre composites by acoustic emission

The design of fibre composites is usually based on the properties and the characteristic values known from material engineering. The components are therefore designed based on the principles of continuum mechanics and the well-known material properties, eventhough a pre-damage caused by aging or even misuse is often responsible for a limited life time. A non-detected pre-damage of the component like fibre breaks, delaminations of pull-out, cracks in the matrix, debonding, fatique and chemical resistance can cause an early failure of the component. Since modern automotive construction is increasingly dependent on fibre composites in fields like series-production vehicles as well as for motorsports, the Fraunhofer IKTS develops in cooperation with an automotive engineering partner monitoring methods in order to determine the material properties of components and the demands for applications in motorsports and for series production non-invasively and also during operation. The proposed technique is based on the fact that dynamical displacements in the nanometer range at the surface of loaded components are detectable by highly sensitive piezoceramic sensors in the frequency range of 50 kHz up to 1 MHz. The advantage of fibre composites is clearly to be defined by the strong acoustic emission caused by fibre cracks and delamination processes. Therefore, this method is successfully applied expecially for fibre composite monitoring wordwide. The paper shows the determination of the material parameters by acoustic emission parameters and the combination of material specific combination of damage mechanisms and the referring parameters of acoustic emission. They make an evaluation of the structural integrity and the reliability of components made from fibre composites possible both before and during operation. Coupon testing with additional acoustic emission measurements on specific specimen geometries give data for a deeper understanding of pre-damage mechanisms and their specific acoustic emission signature