Deformation Behavior Of Amorphous Polymer Research Articles

Experimental and modeling study of the viscoelastic-viscoplastic deformation behavior of amorphous polymers over a wide temperature range

The deformation behavior of amorphous polymers in the post-yield region is viscoelastic-viscoplastic (VE-VP) as it exhibits both viscoelastic and viscoplastic characteristics. However, a systematic experimental and modeling study for it is lacking. In this paper, the VE-VP deformation behavior of an amorphous polymer was experimentally investigated over a wide temperature range. It was found that some of the observed deformation behaviors cannot be reasonably explained by the common assumptions of the thermally-activated segmental motions and the formation of a topologically-entangled rubbery network. With the assumption that there is a glassy network formed from weak linkages in the polymer, the observed deformation behaviors over a wide temperature range can be well explained by considering the stretch and relaxation of the glassy network. The glassy network assumption was first proposed by one of our coauthors and employed for modeling the VE-VP deformation behavior of amorphous polymers at room temperature. In this paper, the glassy network assumption was further examined at different temperatures and employed to establish a constitutive model for simulating the VE-VP deformation behavior of amorphous polymers over a wide temperature range. The model was validated by corroboration with experiments. It was demonstrated that a constitutive model based on the glassy network assumption is capable of representing the loading, strain recovery, and stress relaxation behaviors simultaneously, in contrast to most of the existing constitutive models. Hence, this work not only proposes a reasonable physical picture for understanding but also provides a robust constitutive model for simulating the VE-VP deformation behavior of amorphous polymers and its temperature dependence.

Cooperative viscoplasticity theory based on the overstress approach for modeling large deformation behavior of amorphous polymers

A micromechanically based formulation of the cooperative model is incorporated into the viscoplasticity theory based on overstress (VBO) model. The plastic shear strain rate given by the cooperative model is used as a flow function which is responsible for rate and temperature dependence in the VBO model. In this way, thermomechanical analysis can be performed under different loading rates and temperatures of amorphous polymers. Introducing strain softening, the temperature- and strain-rate-dependent elasticity moduli are two other modifications of the VBO formulation. The validity of the newly proposed cooperative VBO model is demonstrated by modeling the uniaxial compression behavior of poly(methyl methacrylate) under different temperatures and strain rates. © 2013 Society of Chemical Industry

MULTISCALE COMPUTATIONAL EVALUATION OF ELASTO-VISCOPLASTIC DEFORMATION BEHAVIOR OF AMORPHOUS POLYMER CONTAINING MICROSCOPIC HETEROGENEITY DURING UNIAXIAL TENSILE TEST

The two-scale elasto-viscoplastic deformation behavior of amorphous polymer was investigated using the large deformation finite element homogenization method. In order to enable a large time increment for the simulation step in the plastic deformation stage, the tangent modulus method is introduced into the nonaffine molecular chain network theory, which is used to represent the deformation behavior of pure amorphous polymer. Two kinds of heterogeneous microstructures were prepared in this investigation. One was the void model, which contains uniformly or randomly distributed voids, and the other was the heterogeneous strength (HS) model, which contains a distribution of initial shear strength. In the macroscopic scale, initiation and propagation processes of necking during uniaxial tension were considered. The macroscopic nominal stress–strain relation was strongly characterized by the volume fraction and distribution of voids for the void model and by the width of the strength distribution for the HS model. Non-uniform deformation behaviors in microscopic and macroscopic scales are closely related to each other for amorphous polymers because continuous stretching and hardening in the localized zone of the microstructure brings about an increase in macroscopic deformation resistance. Furthermore, computational results obtained from the homogenization model are compared to those obtained from the full-scale finite element model, and the effect of the scale difference between microscopic and macroscopic fields is discussed.

Kinetics of re‐embrittlement of (anti)plasticized glassy polymers after mechanical rejuvenation

AbstractMechanical rejuvenation is known to dramatically alter the deformation behavior of amorphous polymers. Polystyrene (PS)—for example, typically known as a brittle polymer—can be rendered ductile by this treatment, while a ductile polymer like polycarbonate (PC) shows no necking anymore and deforms homogeneously in tensile deformation. The effects are only of temporary nature, as because of physical aging the increasing yield stress, accompanied by intrinsic strain softening, renders PS brittle after a few hours, while for PC necking in tensile testing returns in a few months after the mechanical rejuvenation treatment. In this study, it is found that physical aging upon rejuvenation in both PS and PC can be delayed in two different ways: (1) by reducing the molecular mobility through antiplasticization and (2) by applying toughening agents (rubbery core–shell particles). For the first route, even though progressive aging is found to decrease with increasing amounts of antiplasticizer added, dilution of the entanglement network results in enhanced brittleness. Besides antiplasticization effects, also some typical plasticization effects are observed, like a reduction in matrix Tg. For the second route, traditional rubber toughening using acrylate core–shell modifiers also results in a reduced yield stress recovery, and ductile tensile deformation behavior is observed even 42 months after mechanical rejuvenation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 134–147, 2008

Characterization of micro- to macroscopic deformation behavior of amorphous polymer with heterogeneous distribution of microstructures

In the present study, we clarify the micro- to macroscopic deformation behavior of an amorphous polymer with a slightly heterogeneous distribution of molecular chains; in other words, the distribution of the initial shear strength of the polymer. The micro- to macroscopic deformation behaviors of polymer under macroscopically uniform tension and shearing, uniaxial extension of a plane strain block and surface deformation of the plane strain block under compression were investigated by means of computational simulation with the nonaffine molecular chain network model. The results revealed the onset of microscopic shear bands emanating from slightly weak points and their evolution, and the interaction and percolation of new shear bands. The effects of distribution patterns and standard deviation of initial shear strength on the deformation, the interaction of weak points, the transition from microscopic shear band formation to macroscopic neck propagation and the evolution of surface undulation under compression have been demonstrated.

513 微視的不均一性を有する非晶性高分子材料の変形挙動の評価

513 微視的不均一性を有する非晶性高分子材料の変形挙動の評価

Characterization of Micro-To Macroscopic Deformation Behavior of Amorphous Polymer

Characterization of Micro-To Macroscopic Deformation Behavior of Amorphous Polymer

523 非晶性ポリマーの変形応答のマルチスケールモデルとシミュレーション

523 非晶性ポリマーの変形応答のマルチスケールモデルとシミュレーション