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.

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In this Part I, of a two-part paper, we present a detailed continuum-mechanical development of a thermomechanically coupled elasto-viscoplasticity theory to model the strain rate and temperature dependent largedeformation response of amorphous polymeric materials. Such a theory, when further specialized (Part II) should be useful for modeling and simulation of the thermo-mechanical response of components and structures made from such materials, as well as for modeling a variety of polymer processing operations.

Amorphous thermoplastic polymers are important engineering materials; however, their nonlinear, strongly temperature-and rate-dependent elastic-viscoplastic behavior is still not very well understood, and is modeled by existing constitutive theories with varying degrees of success. There is no generally agreed upon theory to model the large-deformation, thermo-mechanically-coupled, elastic-viscoplastic response of these materials in a temperature range which spans their glass transition temperature. 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.We have numerically implemented our thermo-mechanically-coupled constitutive theory by writing a usermaterial subroutine for a widely-used finite element program. In order to validate the predictive capabilities of our theory and its numerical implementation, we have performed the following validation experiments: (i) a plane-strain forging of PC at a temperature below ϑ g , and another at a temperature above ϑ g ; (ii) blowforming of thin-walled semi-spherical shapes of PC above ϑ g ; and (iii) microscale hot-embossing of channels in Zeonex and PMMA above ϑ g . By comparing the results from this suite of validation experiments of some key 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.

The problem of understanding and modeling the complicated physics underlying the action and response of the interfaces in typical structures under dynamic loading conditions has occupied researchers for many decades. This handbook presents an integrated approach to the goal of dynamic modeling of typical jointed structures, beginning with a mathematical assessment of experimental or simulation data, development of constitutive models to account for load histories to deformation, establishment of kinematic models coupling to the continuum models, and application of finite element analysis leading to dynamic structural simulation. In addition, formulations are discussed to mitigate the very short simulation time steps that appear to be required in numerical simulation for problems such as this. This handbook satisfies the commitment to DOE that Sandia will develop the technical content and write a Joints Handbook. The content will include: (1) Methods for characterizing the nonlinear stiffness and energy dissipation for typical joints used in mechanical systems and components. (2) The methodology will include practical guidance on experiments, and reduced order models that can be used to characterize joint behavior. (3) Examples for typical bolted and screw joints will be provided. 3 AcknowledgmentThe authors thank the many managers and members of technical staff who have worked on this challenging problem at various times since its inception. For all of them, this involved a tremendous amount of hard work and for our management team it involved taking a substantial risk. To put significant resources year-after-year into a problem that had so successfully resisted the best efforts of the scientific community can be a gutsy decision on the part of manager. The authors believe that we have justified our managers' faith in us.Among the managers who should be recognized are