High-speed camera analysis of rupture of polypropylene specimens in tensile tests / Análise das imagens de ruptura de corpos de prova de polipropileno em ensaio de tração obtidas através de câmera de alta velocidade

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

29/07/2011

RESUMO

Injection-molded isotactic polypropylene, iPP, samples present different properties variation as a function of the injection parameters. One of these properties is the rupture propagation on the material, which was studied with the use a high-speed camera adjusted to capture from 18,000 to 45,000 frames per second. The injection molding parameters modified were: cooling time and temperature of the mold. Six groups of specimens were molded and submitted to tensile tests until failure. The rupture images were capture with the high-speed camera. The specimens of the groups 1, 2 and 3 were cooled in the mold at 22 °C during 8, 25 and 55 seconds, respectively. Groups 4, 5 and 6 were cooled in the mold at 80 °C during 8, 25 and 55 s, respectively. Three major rupture patterns associated with the groups were observed. The first pattern, presented by groups 1 and 4, consists in a rapid rupture, with time of propagation between 0.04 and 0.09 ms. A second pattern, observed in groups 2 and 3, presents necking and high elongation, but without a precise time for complete rupture. The third pattern, observed for groups 5 and 6, shows an ellipsoid crack propagation, with an average time for rupture of 1.5 ms. X-Ray diffraction and differential scanning calorimetry measurements were made, but no considerable differences in the degree of crystallinity among the groups was observed. Scanning electron microscopy images of the rupture surface of the specimens showed that there is considerable uniformity in groups 1 and 4. In groups 2 and 3 the appearance of fibrils was observed, whilst for groups 5 and 6 considerable differences between the skin and the core of the specimen was observed. Physical ageing effects on the rupture patterns were studied after the storage of few specimens during 12 weeks. Hardening of the material, due to physical ageing, affected all the groups, but it was most apparent in groups 2 and 3, which started to behave more like the other groups after this time. The result in this work showed that not only the mechanical properties of iPP are affected by the modification in the mold injection parameters, but also the rupture mechanisms can considerably vary. This is observed clearly in the high-speed images.

ASSUNTO(S)

high-speed camera polypropylene tensile test câmera de alta velocidade poliprolileno ensaio de tração

ACESSO AO ARTIGO

Documentos Relacionados