The Fracture Toughness and Morphology Spectrum of Bismaleimide/Polyetherimide Moulding Compounds

Thermoplastic modified bismaleimides (BMI) have found interest as matrix materials for advanced composites with improved damage tolerance. This paper describes the fracture toughness of a bismaleimide/thermoplastic polyetherimide (PEI) system. PEI concentration was varied between 0 and 100% by weight. The stress intensity factor K ***ic was found to increase with increasing thermoplastic content. Up to 20% PEI there was a good agreement between the experimental data and values calculated from a simple rule of mixtures. For higher thermoplastic concentrations fracture toughness was significantly lower than expected by the rule of mixtures. Morphology changes between 20 and 40% by weight caused a local maximum in fracture toughness. BMI/PEI blends were also mechanically characterized. Studies also showed that mini-compact tension test specimens could be used to measure fracture toughness. This results in a significant material saving.