MECHANISMS OF PARTICULATE FILLED POLYPROPYLENE FINITE PLASTIC-DEFORMATION AND FRACTURE

The plastic deformation and fracture of aluminium hydroxide filled pol ypropylene has been investigated. A transition between two mechanisms with an increase of the filler volume fraction has been observed. Belo w a critical filler volume content phi(cr) approximate to 20 vol % (de signated region 1) adhesive failure processes and polymer deformation in the neighbourhoods of different particles occur in an uncorrelated manner. Above this critical value (designated region 2) exfoliation al ong the surface of the initial portion of inclusions causes the format ion of craze-like deformation zones transverse to the direction of the loading. The concentration of craze-like zones is essentially determi ned by the filler content and the level of interphase interaction whic h in turn depends on the particle size. In region 1 deformation occurs in a macro heterogeneous way with the formation and growth of a neck. The elongation to break decreases with an increase in the mean diamet er of the filler phase. At phi > phi(cr) composites, filled with small particles, fail in quasi brittle manner with the formation of a short and narrow neck. In contrast to the case for a small filler concentra tion, an increase of the inclusion size leads to an increase in the ul timate elongation and a tendency to macro homogeneous yielding. An exp lanation of the observed behaviour is proposed based on a change in ad hesive failure conditions with filler content and size.