Cyclic thermo-viscoplasticity of high density polyethylene

Abstract

a b s t r a c tObservations are reported in uniaxial cyclic tensile tests (loading-unloading with various maximum strains) on high density polyethylene at temperatures ranging from room temperature up to 90°C. It is demonstrated that the maximum stress per cycle and an apparent residual strain (measured at the instant when the tensile force vanishes under retraction) strongly decrease with temperature. The latter seems unexpected as the interval of temperatures covers the a-relaxation temperature, which is conventionally associated with activation of additional mechanisms for inelastic flow. A model is developed that captures the decrease in residual strain with temperature. Adjustable parameters in the stress-strain relations are found by fitting the experimental data. The effects of temperature and maximum strain per cycle on residual strains are studied numerically.

Structural mechanics of semicrystalline polymers prior to the yield point: a review

“…However, structural properties are treated implicitly in this approach. Another group of papers [108][109][110][111][112][113][114][115][116][117][118][119][120][121] uses conception of two-phase continuum containing rigid and soft components (crystalline and amorphous phases) with essentially different mechanical properties. The main distinction of semicrystalline polymers from the particulate composites is their peculiar self-organized structure containing stacks of crystal lamellae alternating with thin amorphous layers.…”

“…Application of these ideas for modeling of multicycle deformation behavior of semicrystalline polymers requested to adapt parameters governing intensity of intra-and inter-lamellae plastic flow [100,103,111,140]. To this end, plastic deformation rate of crystalline lamellae _ e p2 was suggested to be considered as a linear function _ e p2 ¼ wr 0 of the deviatoric component r 0 of the macroscopic stress tensor [103,111].…”

“…To this end, plastic deformation rate of crystalline lamellae _ e p2 was suggested to be considered as a linear function _ e p2 ¼ wr 0 of the deviatoric component r 0 of the macroscopic stress tensor [103,111]. In contrast with previous approaches [99], rate of plastic deformation, attributable to the chain sliding, was considered as a linear function _ e p1 ¼ / 2 _ e of the imposed strain rate, where the coefficient / 2 obeys the second order kinetic equation.…”

Time-dependent response of polypropylene after strain reversal

“…This approach was recently used to study the mechanical behavior of semicrystalline polymers by Nikolov and Doghri (2000), van Dommelen et al (2003), Diani et al (2008), Dusunceli and Colak (2008), Baudet et al (2009), Regrain et al (2009), Drozdov (2010a, to mention a few. It provides a simplified description of the micro-structure of polypropylene, where two components of the amorphous phase are conventionally distinguished: mobile (polymer chains in the rubbery state located far away from crystalline lamellae), and rigid (chains with reduced molecular mobility whose thermal motion is severely restricted by surrounding crystallites) (see Hedesiu et al, 2007;Zia et al, 2008).…”

Modeling of viscoplastic cyclic loading behavior of polymers

“…Given that the strain accumulation could be a source of damage accumulation, ratcheting becomes an issue of great importance. Over the last decades, cyclic deformation of polymeric materials has been extensively studied (Pan et al 2010;Ma et al 2011;Zhang et al 2010;Avanzini 2011;Drozdov and Christiansen 2004;Drozdov 2009;and Drozdov 2010). A number of works referring to polyterafluoroethylene (PTFE) (Khan and Zhang 2001;Rae and Dattelbaum 2004;Brown and Dattelbaum 2005) have been performed on the cyclic deformation behavior at various strain rates and temperatures.…”