A thermo-mechanically coupled theory for large deformations of amorphous polymers. Part II: Applications

Abstract

We have conducted large strain compression experiments on three representative amorphous polymeric materials: poly(methyl methacrylate) (PMMA), polycarbonate (PC), and a cyclo-olefin polymer (Zeonex-690R), in a temperature range spanning room temperature to slightly below the glass transition temperature of each material, in a strain rate range of ≈ 10 −4 s −1 to 10 −1 s −1 , and compressive true strains exceeding 100%. The constitutive theory developed in Part I (Anand et al., 2008) is specialized to capture the salient features of the thermo-mechanically-coupled strain rate and temperature dependent large deformation mechanical response of amorphous polymers. For the three amorphous polymers studied experimentally, the specialized constitutive model is shown to perform well in reproducing the following major intrinsic features of the macroscopic stress-strain response of these materials: (a) the strain rate and temperature dependent yield strength; (b) the transient yield-peak and strain-softening which occurs due to deformation-induced disordering; (c) the subsequent rapid strain-hardening due to alignment of the polymer chains at large strains; (d) the unloading response at large strains; and (e) the temperature rise due to plastic-dissipation and the limited time for heat-conduction for the compression experiments performed at strain rates 0.01 s −1. We have implemented our thermo-mechanically-coupled constitutive model by writing a user material subroutine for the finite element program ABAQUS/Explicit (2007). In order to validate the predictive capabilities of our constitutive theory and its numerical implementation, we have performed the following validation experiments: (i) isothermal fixed-end large-strain reversed-torsion tests on PC; (ii) macroscale isothermal plane-strain cold-and hot-forming operations on PC; (iii) macroscale isothermal, axi-symmetric hot-forming operations on Zeonex; (iv) microscale hot-embossing of Zeonex; and (v) high-speed normal-impact of a circular plate of PC with a spherical-tipped cylindrical projectile. By comparing the results from this suite of validation experiments of some key macroscopic features, such as the experimentally measured deformed shapes and the load-displacement curves, against corresponding results from numerical simulations, we show that our theory is capable of reasonably accurately reproducing the experimental results obtained in the validation experiments.

A thermo-mechanically-coupled large-deformation theory for amorphous polymers in a temperature range which spans their glass transition

“…Such a theory is crucial for the development of a numerical capability for the simulation and design of important polymer processing operations, and also for predicting the relationship between processing methods and the subsequent mechanical properties of polymeric products. In this paper we extend our recently published theory , IJP 25, 1474-1494Ames et al, 2009, IJP 25, 1495-1539 to fill this need.…”

“…Such a theory is crucial for the development of a numerical capability for the simulation and design of important polymer processing operations, and also for predicting the relationship between processing methods and the subsequent mechanical properties of polymeric products. In this paper we extend our recently published theory , IJP 25, 1474-1494Ames et al, 2009, IJP 25, 1495-1539 to fill this need.We have conducted large strain compression experiments on three representative amorphous polymeric materials -a cyclo-olefin polymer (Zeonex-690R), polycarbonate (PC), and poly(methyl methacrylate) (PMMA) -in a temperature range from room temperature to approximately 50C above the glass transition temperature, ϑ g , of each material, in a strain-rate range of ≈ 10 −4 to 10 −1 s −1 , and compressive true strains exceeding 100%. We have specialized our constitutive theory to capture the major features of the thermomechanical response of the three materials studied experimentally.…”

A large strain hyperelastic viscoelastic-viscoplastic-damage constitutive model based on a multi-mechanism non-local damage continuum for amorphous glassy polymers

“…In the literature, the nonlinearity upon unloading of glassy polymers can be modeled by considering a nonlinear viscoeslastic behavior as demonstrated by Xia et al (2005Xia et al ( , 2006; Colak (2005); Anand and Ames (2006). The constitutive models considering the kinematic hardening can account for this nonlinear response at large strains Ames et al, 2009), however they do not adequately account for this effect at small strains (Anand and Ames, 2006). Additionally, the heat generation and thermal conduction due to plastic dissipation become important at large strains and can affect both loading and unloading responses as demonstrated by Anand et al (2009);Ames et al (2009).…”

“…The constitutive models considering the kinematic hardening can account for this nonlinear response at large strains Ames et al, 2009), however they do not adequately account for this effect at small strains (Anand and Ames, 2006). Additionally, the heat generation and thermal conduction due to plastic dissipation become important at large strains and can affect both loading and unloading responses as demonstrated by Anand et al (2009);Ames et al (2009). A nonlinear viscoelastic model, heat generation, and thermal conduction will be considered in a future work in a fully thermo-mechanically-coupled simulation.…”

Multi-mechanism modeling of amorphous polymers

“…Various models were developed and tested to simulate these responses. Rheological models extended to three-dimensional case under finite strain assumption have been proposed, for instance, by (Alcoutlabi and MartinezVega, 2003;Anand and Ames, 2006;Dupaix and Boyce, 2007;Ames et al, 2009;Anand et al, 2009;Srivastava et al, 2010;Shim and Mohr, 2011;Fleischhauer et al, 2012;Helbig and Seelig, 2012). Some of them were devoted to phenomenological modeling (Zaïri et al, 2005b;Cheng and Ghosh, 2013) or developed within a thermodynamics framework (Drozdov, 1999;Miehe et al, 2009;Bouvard et al, 2013).…”