Application of the essential work of fracture method in ranking the performance in service of high-density polyethylene resins employed in pressure pipes
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High-density polyethylene resins have increasingly been used in the production of pipes for water- and gas-pressurized distribution systems and are expected to remain in service for several years, but they eventually fail prematurely by creep fracture. Usual standard methods used to rank resins in terms of their resistance to fracture are expensive and non-practical for quality control purposes, justifying the search for alternative methods. Essential work of fracture (EWF) method provides a relatively simple procedure to characterize the fracture behavior of ductile polymers, such as polyethylene resins. In the present work, six resins were analyzed using the EWF methodology. The results show that the plastic work dissipation factor, βwp, is the most reliable parameter to evaluate the performance. Attention must be given to specimen preparation that might result in excessive dispersion in the results, especially for the essential work of fracture we.
KeywordsPlastic Zone Linear Elastic Fracture Mechanic Stable Crack Growth Ligament Length Pressure Pipe
We are grateful to Braskem S.A., Dow Latin America, Ipiranga Petroquímica and Solvay Indupa do Brasil S.A. for providing the base resins and the corresponding “regression curves” and to Cromex S.A. (São Paulo-SP, Brazil) for the extrusion of the films. The assistance of Mr. Leonardo di Nino in the tests is gratefully acknowledged. This work has been partially supported by the Brazilian National Research, Development and Innovation Council (CNPq, Brasília-DF, Brazil) with grants under projects PIBIC/USP and Proc. 302508/2003-1.
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