STRESS-STRAIN BEHAVIOR AND TENSILE DILATOMETRY OF GLASS BEAD-FILLED POLYPROPYLENE AND POLYAMIDE-6

The mechanical behavior of multiphase materials is closely related to the interfacial adhesion between their various components. There is co nsiderable interest in the development of simple experimental techniqu es for characterization of interfacial debonding during mechanical loa ding. Probably the best known method is tensile dilatometry, in which the onset and progression of debonding are related to the volume of mi crovoids generated in the material as it undergoes mechanical loading. Several authors have suggested that equivalent information can also b e extracted from stress-strain data generated during a simple constant strain rate test. In practice, however, the transition between the in itially well-bonded and the debonded state is obscured by the strain-i nduced softening of the matrix, which is usually observed in the same strain range as the debonding. In this work the filler/matrix debondin g in polypropylene and polyamide 6 filled with up to 50 vol % of glass beads is examined using both tensile dilatometry and an analysis of t ensile stress-strain curves. It was found that, depending on the level of adhesion, either a complete or partial debonding occurs in the str ain range studied (0-8%). It appears that the volume change due to deb onding is a small part of the total volume strain recorded. Therefore, the accuracy of the tensile dilatometry is not sufficient to detect t he onset of debonding. The loss of stiffness of the composite, particu larly when compared to the loss of stiffness of the matrix offers a mo re promising way to follow the debonding process. (C) 1997 John Wiley & Sons, Inc.