Time-dependent response of polypropylene after strain reversal

Abstract

a b s t r a c tObservations are reported in tensile relaxation tests on specimens subjected to stretching up to various maximum strains max followed by retraction to various minimum strains . Experimental data show that shapes of relaxation curves on pre-loaded samples are strongly affected by strain increment D = max À : (i) when D is small, stress monotonically decays with time, (ii) with an increase in D, the relaxation process becomes non-monotonic, and (iii) at relatively large increments D, stress grows with time. A two-phase constitutive model is derived for the viscoelastic and viscoplastic responses of semicrystalline polymers under arbitrary deformations with small strains. Adjustable parameters in the stress-strain relations are found by fitting the observations. Numerical simulation demonstrates that the model correctly describes the time-dependent behavior of polypropylene subjected to cyclic preloading in creep and relaxation tests.

Cyclic viscoelastoplasticity and low-cycle fatigue of polymer composites

“…A reason for this simplification is that such phenomena as (i) ''unusual'' viscoelastic response observed in relaxation tests after partial retraction (Kitagawa et al, 1995;Khan, 2006;Drozdov, 2010b), and (ii) evolution of relaxation spectrum induced by damage accumulation (Jin and Wang, 2009) are disregarded in the model. Accuracy of this assumption will be discussed in Section 6.…”

Experimental investigations and modeling of volume change induced by void growth in polyamide 11

“…Other studies were devoted to the modeling of the viscoplastic behavior of polyamide 66 (Krempl et al, 1984;Krempl and Ho, 2000). To take the multiaxial stress-state under visco-elasticity and/or visco-plasticity constitutive models were recently developed by Van Domellen et al (2003) under monotonic loading, by Drozdov (2010) and Ayoub et al (2010Ayoub et al ( , 2011 under strain reversal loading and by Ben Hadj Hamouda et al (2007) and Regrain et al (2009) for creep loading. These models generally take the degree of crystallinity into account but not the volume change.…”

Mechanical response of HEMA gel under cyclic deformation: Viscoplasticity and swelling-induced recovery

“…As relaxation tests are conducted on equilibrated samples with a fixed degree of swelling, U is treated as a parameter. The following equation for the time-dependent decay in stress is accepted (Drozdov, 2010): rðsÞ ¼ r 0 1 À j Z 1 0 pðuÞdu Z s 0 1 À exp Àc expðÀbuÞðs À sÞ ð Þ ð Þ ds ! :…”

“…sample, and the difference between these curves is weakly affected by duration of rest (Drozdov, 2007). The decrease in k min with time is conventionally called inverse creep, and its kinetics has recently been analyzed in several studies, see Drozdov (2010) and Drozdov and Christiansen (2013a), and the bibliography therein.…”