Fatigue Crack Propagation Evaluation of Different Commercial Grade Propylene Polymers

J. WAINSTEIN; M.D. CHAPETTI; P. MONTEMARTINI; P. FRONTINI

International Journal of Polymeric Materials

Taylor and Francis Ltd

Año: 2005 vol. 54 p. 575 - 587

0091-4037

Results of an experimental evaluation of commercial propylene polymers´ performance under cyclic loading are reported. Experiments were conducted on one extrusion grade homopolymer and one impact block copolymer. The influence of thermal annealing was taken into account on the homopolymer. A laboratory-made mechanical fatigue unit capable of applying sinusoidal displacement was used to conduct fatigue tests on precracked specimens in three points bending at room temperature. Materials exhibit different crack propagation modes. The neat homopolymer displays discontinuous-catastrophic crack propagation. Both copolymer and annealed homopolymer show longer fatigue lifetime but faster propagation rates than the neat homopolymer. The annealed homopolymer also propagates in a step-like way whereas the block copolymer displays a continuous crack propagation mode in which the crack advances regularly as cycling proceeds. A noticeable crack front damage (identified as stress whitening) is developed at the crack root, which seems to control the crack propagation rate