Zusammenhänge zum Schlagzähigkeits‐ und Durchstoßverhalten thermoplastischer Natur‐/Langfaserverbunde

Correlations for the fracture work and falling weight impact properties of thermoplastic natural / long fibre composites The improvement of the fracture work is of special importance for the expansion of application fields in plastics construction parts of enhanced stress characteristics. An improvement of the toughness properties can be achieved by increased deformation ability. Fracture work and energy at the falling weight impact tests can be raised both by increasing of the strength and/or elongation of the reinforcing fibres and by reduction of the adhesion. The reduction of adhesion can be realized using no compatibilizers. But the increasing of the strength and/or elongation is restricted. The deformation ability of the resulting composite can be increased by addition of fibre components of higher strength respectively elongation to the natural and matrix fibres during manufacturing of the precursor. Significant improvements of the impact strength of such composites could be proved by impact bending tests and by measuring of strength and energy in breaking tests at shock load by falling weight tests. The results of both tests were compared to find out the origin of the improvement. It was found that the energy E_p needed for crack initiation has only a negligible effect on the improvement of the fracture work a_cU (Charpy impact strength). A significant higher effect on the fracture work a_cU was found for the energy E_r which will force the crack extension. So the increased crack retardation energy caused by the mechanical properties of the added fibres can be seen as the main origin of the improved toughness properties transition obtained by addition of fibres of high strength respectively elongation.