Issue 42

M. Peron et alii, Frattura ed Integrità Strutturale, 42 (2017) 214-222; DOI: 10.3221/IGF-ESIS.42.23 214 Local strain energy density for the fracture assessment of polyurethane specimens weakened by notches of different shape M. Peron, S.M.J. Razavi ,F. Berto, J. Torgersen Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), Richard Birkelands vei 2b, 7491, Trondheim, Norway. mirco.peron@ntnu.no, javad.razavi@ntnu.no, filippo.berto@ntnu.no , jan.torgersen@ntnu.no L. Marsavina Department of Mechanics and Strength of Materials, Univeritatea Politehnica Timisoara, Timisoara, Romania msvina@mec.upt.ro A BSTRACT . Recent studies on local stress fields in proximity of crack and notch tips have shown that Strain Energy Density (SED), averaged in a circular control volume surrounding the point of stress singularities, represents a reliable engineering approach for assessing the brittle fracture of several brittle materials. It is worthy of notice that the application of SED criterion and the reliability of its results are strictly related to the proper determination of fracture parameters, i.e. the critical value of deformation energy W c and the radius R c of the control volume. This work presents an experimental methodology for their determination by means of notched specimens for different polyurethane densities, ranging from 100 to 651 kg/m 3 . Then, once obtained these critical parameters, the failure load in different types of notches and cracked specimens under mode I have been predicted. Moreover, for cracked specimens under mixed mode and mode II, the authors propose a personal approach that confirms PUR foams can be treated as brittle materials K EYWORDS . Strain Energy Density; PUR foams; Tensile fracture; Critical radius; Fracture parameters. Citation: Peron, M., Razavi, S.M.J., Berto, F. Torgersen, J., Marsavina, L., Local strain energy density for the fracture assessment of polyurethane specimens weakened by notches of different shape, Frattura ed Integrità Strutturale, 42 (2017) 214-222. Received: 28.06.2017 Accepted: 31.07.2017 Published: 01.10.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION n the last years, Polyurethane (PUR) has widely gained interest in industrial applications because of its high versatility. In fact, as other polymers like polyethylene (PE), PUR materials can be manufactured in a wide range of densities, obviously determining different applications. In fact at low densities (30 - 200 kg/m 3 ), being rigid foams having a close cell cellular structure, they are employed as high-resilience seating, rigid foam insulation panels, microcellular foam seals and gaskets, high durable elastomeric wheels and tires and as automotive suspension bushings [1]. Whereas, at higher I

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