Modelling of creep behaviour in injection-moulded HDPE

Thermo-viscoelastic and viscoplastic behavior of high-density polyethylene

“…The apparent yield stress r y monotonically grows with strain rate _ (from 14.8 MPa at _ ¼ 2 Â 10 À4 s À1 to 22.6 MPa at _ ¼ 4 Â 10 À2 s À1 ), whereas the apparent yield strain y is practically independent of strain rate. These results are in agreement with findings reported by other authors (Beijer and Spoormaker, 2000;Dasari and Misra, 2003;Elleuch and Taktak, 2006).…”

“…In the past decade, the time-and rate-dependent responses of polyethylenes at ambient conditions, as well as at elevated temperatures have been studied in a number of publications, see Zhang and Moore (1997), Nitta and Suzuki (1999), Beijer and Spoormaker (2000), Djokovic et al (2000), Pegoretti et al (2000), Mano et al (2001), van Dommelen et al (2003), Dasari and Misra (2003), Bergstrom et al (2004), Hong et al (2004), Remond (2005), Mrabet et al (2005), Nikolov et al (2006), Colak and Dusunceli (2006), Elleuch and Taktak (2006), Christiansen (2007a,b), andBen Hadj Hamouda et al (2007), to mention a few. Although several variants of constitutive equations have been proposed for the viscoelastic and viscoplastic behavior of semi-crystalline polymers that reveal an acceptable agreement with observations, these models share common shortcomings: (i) they disregard thermally-induced evolution of microstructure of HDPE in the vicinity of a-relaxation point (in the interval of temperatures between 60 and 80°C), and (ii) their application to fitting observations results in rather high values of the apparent activation energy of solid polyethylene (in the interval between 100 and 200 kJ/mol) which substantially exceed those for polyethylene melts [20-30 kJ/mol (Bin Wadud and Baird, 2000)] and are close to the activation energies for thermal degradation of high-density polyethylene [ranging between 200 and 300 kJ/ mol (Sinfronio et al, 2005;Marazzato et al, 2007)].…”

Creep behavior of high density polyethylene after aging in contact with different oil derivates

“…1. For larger stress values, that is to say r 0 [ 0.1 MPa, the creep behavior is more affected by the value of the applied stress: the viscoelastic response of the original HDPE is now nonlinear as often reported in the literature [9][10][11][12].…”

“…For some authors, the dependence of the HDPE compliance with the applied stress can be described using the Leaderman model that is based on the separation of the stress and time functions [9,10]. Different models tried to relate the nonlinear creep of a polymer with molecular mechanisms.…”

The Nonlinear Time‐Dependent Response of Semicrystalline Polymers: Correlations Between the Configurational Entropy and the Rate of Rearrangement of Chains

“…The stress-strain Equation (29) is valid for an arbitrary deformation program. In the general case, however, it requires the knowledge of the function nðt; ; vÞ that is governed by integro-differential Equation (11) and (13).…”