30 Retarded Necking in Continuous NylonFiber Reinforced Polypropylene M. R. KANTZ and R. D. CORNELIUSSEN
Downloaded by COLUMBIA UNIV on July 9, 2013 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0154.ch030
Department of Materials Engineering, Drexel University, Philadelphia, Pa. 19104
The tensile properties of isotactic polypropylene materials reinforced with continuous nylon fibers were measured. Less than 10 vol % of the fibers leads to an increased yield strength and yield elongation. As little as 3 vol % of the nylon fibers increased the elongation at necking from 10 to 20%. This retarded necking arises from the fiber-matrix debonding which delocalizes the microscopic yielding processes.
Reinforcement of metallic and polymeric materials with high modulus fibers and particles generally leads to reduced tensile elongation or ductility. According to Nielsen (I) the reduction in the ultimate elongation of the composite varies systematically with the volume fraction of reinforcing particles, V , for particulate reinforced materials in which the adhesion between the two phases is "perfect." This relationship is given as: r
-?! _ (1 _ y i/s)
(1)
r
Cm
where c and c are the ultimate elongations of the composite and matrix. The validity of this model has been demonstrated for certain glass-bead reinforced thermoplastic and thermosetting resins (2, 3, 4). It has been reported (2), however, that increasing the adhesion between glass beads and an epoxy matrix using a coupling agent gave higher values of c than predicted by Nielsen (I). In recent work involving glass-bead filled amorphous thermoplastics such as polystyrene, styrene/acrylonitrile copolymers, and polyphenylene oxide, the elongation of the composite was greater than the elongation of the matrix when the tensile test was carried c
m
c
367 In Toughness and Brittleness of Plastics; Deanin, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
TOUGHNESS AND BRITTLENESS O F PLASTICS
368
out above the brittle-ductile transition temperature (3, 4). This behavior was attributed to debonding, craze nucleation, and subsequent termination of craze propagation by notch blunting at weak phase boundaries (4). During our study of the tensile behavior of isotactic polypropylene containing low volume fractions ( < 10%) of continuous thermoplastic fibers we found that the composite yield strength (
