EFFECTS OF FILLERS ON FRACTURE PERFORMANCE OF THERMOPLASTICS - STRAIN-ENERGY DENSITY CRITERION

This paper presents the experimental results on the fracture performance of filled thermoplastics. The emphasis is put on verification of the validity of different fracture criteria. The effects of two- and three-dimensional fillers on the fracture toughness of a representative thermoplastic, polypropylene, are analyzed. It has been found that classical fracture mechanics do not properly describe the fracture behavior of these composites. The strain energy density theory provides a more appropriate criterion for predicting fracture. On the macroscopic scale, the addition of fillers leads to a reduction in the critical strain energy density of thermoplastics. However, on the microscopic level fillers enhance a more wide spread crack-growth and failure by fracture becomes more stable. The material is therefore less prone to shatter in service. This effect of fillers is interpreted in terms of damage development, induced by the debonding at the matrix/fillers interface. A better interfacial adhesion reduces the microscopic damage and the critical increment of crack growth prior to instability. The results explain the negative effect of coupling agent on the impact resistance observed in practice. © 1990.