Fracture behavior of polymer composites with fillers coming from natural sources

C. BERNAL AND A. VÁZQUEZ

Ventura, California, USA

Conferencia; Gordon Research Conference: Composites; 2006

Gordon Research Conference

The fracture behavior of two different natural filler reinforced polymer composites was investigated under different loading conditions. Woven jute fabric/vinylester laminates, high impact polystyrene reinforced with short sisal fibers, and organic ash/PP composites were studied. Several factors such as filler content, interfacial adhesion between filler and matrix, and testing conditions were found to affect the fracture behavior of these composites. Different conventional fracture mechanics methodologies were proven to be useful to characterize the materials response depending on the material fracture behavior. LEFM parameters such as the critical energy release rate (GIC) and the critical stress intensity factor (KIC) were adopted when the material behaved in a brittle or semi-brittle fashion. In contrast, J-Integral concept and the Essential Work of Fracture method were used when extensive yielding was observed during fracture. In the case of woven jute fabric/vinylester laminates, the critical energy release rate was used to determine the effect of fabric treatment on the material fracture toughness. On the other hand, sisal reinforced HIPS exhibited ductile behavior under both quasi-static and impact loading conditions. Therefore, J-Integral concept through the Normalization method and the Essential Work of Fracture methodology were adopted to characterize quasi-static and impact fracture behavior, respectively based on the experimental simplicity in each case. A maximum in the quasi-static fracture toughness with fiber loading was found as a result of a competition between fiber-related toughening and rubber-related toughening. In contrast, sisal/HIPS composites exhibited impact fracture toughness values lower than the neat matrix due to the combined effect of the matrix embrittlement under impact loads and the restriction to matrix yielding imposed by the sisal fibers. For organic ash/PP composites, the critical stress intensity factor was chosen to characterize fracture initiation. Although the incorporation of organic ash to PP was detrimental to the resistance to fracture initiation under quasi-static and impact loading conditions, quasi-static fracture behavior was observed to change from a semi-brittle mode of fracture in the neat PP matrix to a completely stable in the composites. Hence, a significant improvement in the quasi-static crack propagation resistance of the composites was found as more energy was absorbed by the specimens to fracture.