Fracture mechanics parameters for polystyrene under high speed impact

✍ Scribed by D. G. Cook; A. Rudin; A. Plumtree

• Publisher: Society for Plastic Engineers
• Year: 1990
• Tongue: English
• Weight: 735 KB
• Volume: 30
• Category: Article
• ISSN: 0032-3888
• DOI: 10.1002/pen.760301006

✦ Synopsis

Abstract

A series of commercial polystyrenes was tested using an instrumented impact tester to determine the fracture toughness K~c~ and critical strain energy release rate G~c~. Over the range of M~w~, 201,000 to 336,000, K~c~ increased from 1.38 MN/m^3/2^ to 1.76 MN/m^3/2^and G~c~ from 0.92 kJ/m^2^ to 1.60 kJ/m^2^. A linear correlation for K~c~ and G~c~ was seen with melt index, and an inverse relationship was obtained against molecular weight. Examination of the fracture surfaces revealed the presence of crack growth bands corresponding to the crack tip plastic zone size. It is suggested that these bands are the consequence of variations in crack growth along crazes that form in the crack tip stress field. As the crack propagates, the stress is relaxed locally, decreasing the growth rate allowing a new bundle of crazes to nucleate along which the crack advances. The spacing of these bands corresponds to the craze length formed in the plastic zone, and the band spacing increases with molecular weight.