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Effects of loading rate on fracture properties and failure mechanism of polypropylene/clay nanocomposites

[ jeudi 21-06-2007 13:00 | anglais ]Effects of loading rate on fracture properties and failure mechanism of polypropylene/clay nanocomposites Prof. Naresh Bhatnagar Dept of Mechanical Engineering, Indian Institute of Technology Delhi
Résumé :
Polypropylene (PP)/clay (5% by weight) nanocomposite was prepared by melt compounding with maleic anhydride grafted polypropylene (MA-g-PP) compatibilizer in a twin screw extruder, and the test specimens were injection molded. The PP/clay nanocomposite was characterized by XRD and SEM. XRD results show possibilities of exfoliation and SEM studies rules out large-scale particle agglomeration. Mechanical properties such as tensile modulus, flexural modulus, yield strength and maximum percent strain are presented. The fracture properties were measured by using essential work of fracture method (EWF). PP/clay nanocomposite shows 25% improvement in specific essential work of fracture compared to pure PP. The variation of EWF parameters with loading rate is also presented. Fractographic observations of PP/clay nanocomposite at lower loading rates, reveal that excessive fibrillation and impregnated fibrils arrest crack propagation, and the fracture occurs by void initiation at larger clay particles. As the loading rate increases, crazes combines with voids to accelerate crack propagation. At higher loading rates, cleavage type brittle fracture was observed. A new failure mechanism of nanocomposite material is also proposed.