Strain damage and fracture properties of glass bead filled polypropylene

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Abstract

The effects of glass-bead content and glass-bead size on strain damage and fracture properties of glass bead/polypropylene (GB/PP) composites have been investigated. Ten different GB/PP composites were prepared using two different diameters: 4μm and 49μm, and five different volume percentage: 5%, 10%, 15%, 20% and 25% of glass bead. Strain damage behaviour of the composites was determined using injection-moulded tensile specimens through load-and-unload tensile tests. The stiffness of all the composites was found to decrease with increasing strain after a certain threshold strain. Owing to debonding-induced damage occurring in the composites, the progressive loss of the stiffness for the composites after undergoing the straining process was more severe than that of unfilled PP, and became serious as the glass-bead content and glass-bead size were increased. Fracture toughness measurements were made using compact tension (CT) specimens. The fracture toughness KQvalues were calculated using 5% offset load P5%in accordance with ASTM E399, KQof the filled composites were found to be higher than that of the unfilled PP. The 4μm glass-bead composite had the KQvalues greater than the 49μm glass-bead composite. It could be related to their differences in interparticle spacing. A small amount of non-linearit up to crack initiation was found for unfilled PP. The degree of non-linearitydue to debonding-induced damage became significant when the glass-bead content and size were increasing. Rapid photographic procedures were used to identify the crack-initiation load Pciand describe the crack growth behaviour. It was found that P5%and Pcidid not coincide. The difference of Pciwith respect to P5%was only 5.6% for unfilled PP. The values of Pciwere 12 to 55% greater than those of P5%for the 4μm glass-bead composite and 57 to 88% larger than those of P5%for the 49μm glass-bead composite. Owing to such large difference and large amount of non-linearity, linear fracture mechanics may not be well suitable for describing the fracture properties of unfilled PP and GB/PP composites. GB/PP composites failed in much more ductile manner than unfilled PP. The interfacial bonding quality could be reflected from the tensile strength according to the Nicolais and Nicodemo equation. The fractured CT specimens were examined by scanning electron microscopy. It was revealed that poor bond coupling between the glass beads and the PP matrix may result in the decrement of KQas compared with unfilled PP.
Original languageEnglish
Pages (from-to)395-406
Number of pages12
JournalEuropean Structural Integrity Society
Volume27
Issue numberC
DOIs
Publication statusPublished - 1 Dec 2000

Keywords

  • deformation
  • fracture mechanics
  • glass bead filled
  • Polypropylene
  • strain damage

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Mechanics of Materials

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