Paper number 550

CRACK MICROSTRUCTURE DURING THE CARBONIZATION OF CARBON FIBRE REINFORCED PLASTICS TO CARBON/CARBON COMPOSITES

J. Schulte-Fischedick¹, M.Frieß¹, W.Krenkel¹, R.Kochendörfer¹ and M.König²

1Institute of Structures and Design, German Aerospace Center (DLR),
Pfaffenwaldring 38/40, 70569 Stuttgart
2Institute of Statics and Dynamics in Aerospace Structures, University of Stuttgart,
Pfaffenwaldring 27, D- 70550 Stuttgart

Summary

The major process for manufacturing carbon/carbon composites is the carbonization of carbon fibre reinforced plastics (CFRP). In this process, the shrinkage of the matrix is hindered by the fibres and leads to a high amount of cracks resulting in a microscopic open porosity. To control this process, it is necessary to gain knowledge about its essential parameters, in which the crack microstructure plays an important role. Micrographs (SEM) revealed that the cracks can be distinguished in three different types: fibre-matrix debonding, segmentation cracks and micro-delaminations. Fibre-matrix bonding determines which crack type dominates the structure of the final carbon/carbon composite. The evolution of the cracks during pyrolysis (temperature, sequence and importance of the crack types) was investigated by means of acoustic emission and microscopy in combination with a heating stage. By comparing these results with those of thermogravimetric analysis and dilatometer experiments, the development of the cracks can be explained.

Keywords

carbon/carbon composites, CFRP, carbonization, microstructure, crack evolution, heating stage, acoustic emission.