Fracture energy of polymers at low temperatures

✍ Scribed by T. Saatkamp; G. Hartwig

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 328 KB
• Volume: 31
• Category: Article
• ISSN: 0011-2275
• DOI: 10.1016/0011-2275(91)90082-8

✦ Synopsis

Investigation of crack propagation is one method for describing fracture behaviour. Crack propagation has therefore been investigated for two very different polymers, polyethylene (HDPE) and polystyrene (PS), at different cross-head speeds and the fracture energy has been extracted from these measurements. Only at very slow cross-head speeds (v _< 9 x 10 -8 m s -1) and at elevated temperatures (77 K) was stable crack growth observed for HDPE. At increased cross-head speeds or decreased temperatures crack propagation becomes unstable. Temperature and deformation rate control the process occurring at a crack tip. For unstable crack propagation, most polymers show crack arrest (slip-stick) behaviour which arises from adiabatic heating and plastic deformation at the crack tip. Due to the small specific heat at low temperatures even a small deposition of inelastic deformation energy leads to an appreciable temperature rise. Under certain conditions adiabatic heating is high enough to reach a secondary dispersion region of a polymer where enhanced plastification occurs. The fracture energy is increased by these processes. Another type of process occurring at the crack tip is the formation of crazes which increases fracture energy. This might be true for PS above 77 K. The behaviour of crack propagation at different temperatures and cross-head speeds is also discussed.