FRACTURE TOUGHNESS OF CR TYPES OF POLYPROPYLENE COPOLYMER WITH IMPACT RESISTANCE

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In this work, the introductory study of determination of fracture toughness of materials with controlled rheology based on the same kind of impact copolymer polypropylene is presented. Measurements were carried out using two types of samples SENB and CT, whereas SENB samples were measured in quasi - dynamic mode and CT samples in static mode. Quasidynamic measurements were performed on instrumented Charpy pendulum at laboratory temperature (23 centi degree) and at low temperature ( - 20 centi degree). The unstable fractures of materials were observed at low temperature and for brittle materials also at laboratory temperature. Fracture toughness was evaluated using Sumpter and Turner J (ST Id) integral formula. The stable fractures of materials were observed for tough materials. Fracture toughness was evaluated on the basis of crack resistance (R) curves. J(R) values were plotted as a function of stable crack growth a, which was realized using stopblock method. CT samples were tested in tensile mode at laboratory temperature. Stable fractures were observed for all materials. Fracture toughness was determined by J(R) curve concept similar to the SENB specimens. Fracture toughness values gained from static and quasidynamic mode showed monotone decrease according to the melt flow index of materials prepared by control rheology procedure.

fracture toughness, stable fracture, unstable fracture, J(ST ID)- integral

SADÍLEK, J.; KUČERA, J.; ŠIMKOVÁ, P.

12. 9. 2007

FCH VUT

FCH, VUT Purkyňova 118, 61200 Brno