Deformation Of Glassy Polymers Research Articles

Plasticity Mechanism for Glassy Polymers: Computer Simulation Picture

This review summarizes the data published over the past two and a half decades on the mechanism of plastic deformation of bulk isotropic linear glassy polymers in uniaxial tension, compression, and shear at low deformation temperatures (Тdef < 0.6Тg) and moderate loading rates. The main attention is focused on studies concerning the numerical computer simulations of plasticity of organic polymer glasses. The plastic behavior of glassy polymers at nano-, micro-, and macrolevels in the range of macroscopic strains up to ≈100% is discussed. Plasticity mechanisms are compared for organic, inorganic, metallic, polymer, and nonpolymer glasses with different chemical structures and types of interparticle interactions. The general common mechanism of plasticity of glassy compounds, the nucleation of plasticity carriers in them, and the structure of such carriers and their dynamics are covered. Within the framework of the common plasticity mechanism, the specific features of deformation in glassy polymers are analyzed. Specifically, the participation of conformational transformations in macromolecules in the deformation response of polymer glasses, change in intensity of the yield peak with the thermomechanical prehistory of the sample, and the role of van der Waals interactions in the accumulation of excess potential energy by the sample under loading are considered. The role of free volume and structural and dynamic heterogeneities in the plasticity of glasses is also discussed.

Stepwise mechanism of the nucleation of plastic deformation in glassy polymers

The mechanism was studied for the nucleation of inelastic strain (its delayed elastic (anelastic) component ede and plastic component ep) during isothermal loading of specimens of organic glassy polymers of various chemical nature by uniaxial compression at Tdef < 0.6 Tg within the strain range edef < 45–50%.

On the nature of abnormalities in the structural mechanical behavior of glassy polymers

Literature data on abnormalities in the mechanical behavior (stress relaxation in the initial section of the stress-strain (compression) diagram, stress growth under isothermal heating, a low-temperature contribution to the temperature-induced strain recovery of deformed polymer glasses, a soft compliant phase upon the tensile drawing of a glassy polymer revealed by dynamic mechanical tests) and in the thermophysical behavior (accumulation of internal energy at early stages of deformation and an exothermic DSC peak below the glass transition temperature) of the deformed glassy polymers are considered. The above abnormalities can be explained taking into account two fundamental features of amorphous polymers, first, the inhomogeneous character of inelastic deformation in glassy polymers, which leads to the development of discrete regions of plastically deformed material in the initial polymer (shear bands and/or crazes), and, second, a marked decrease in T g of highly dispersed oriented material filling both shear bands and crazes.

A Microstructure-Level Material Model for Simulating the Machining of Carbon Nanotube Reinforced Polymer Composites

A continuum-based microstructure-level material model for simulation of polycarbonate carbon nanotube (CNT) composite machining has been developed wherein polycarbonate and CNT phases are modeled separately. A parametrization scheme is developed to characterize the microstructure of composites having different loadings of carbon nanotubes. The Mulliken and Boyce constitutive model [2006, “Mechanics of the Rate Dependent Elastic Plastic Deformation of Glassy Polymers from Low to High Strair Rates,” Int. J. Solids Struct., 43(5), pp. 1331–1356] for polycarbonate has been modified and implemented to capture thermal effects. The CNT phase is modeled as a linear elastic material. Dynamic mechanical analyzer tests are conducted on the polycarbonate phase to capture the changes in material behavior with temperature and strain rate. Compression tests are performed over a wide range of strain rates for model validation. The model predictions for yield stress are seen to be within 10% of the experimental results for all the materials tested. The model is used to study the effect of weight fraction, length, and orientation of CNTs on the mechanical behavior of the composites.

3D Numerical Simulation of the Deformation of Glassy Polymer

The objective of the work is to numerically study the meso-scale deformation of amorphous glassy polymer. A molecular polymerization algorithm is employed to generate three-dimensional (3D) random networks of polymer, in which the micro-parameters and meso-structures, such as entanglement point, sliding point, etc. are considered. Then, 3D unit cell model and finite element method are used to calculate the stress and deformation relations of polymer. The evolution of meso-structure of glassy polymer with deformation is obtained simultaneously. Further, variation of the orientation of polymer chain with deformation was quantitatively studied.

Multiscale Modeling for Large Deformation of Glassy Polymer Based on Molecular Chain Slip Model and Probabilistic Response Law of Inelasticity

Multiscale Modeling for Large Deformation of Glassy Polymer Based on Molecular Chain Slip Model and Probabilistic Response Law of Inelasticity

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Simulation of plastic deformation in glassy polymers: Atomistic and mesoscale approaches

AbstractThe mechanism of deformation in glasses is very different from that of crystals, even though their general behavior is very similar. In this study, we investigated the deformation of polycarbonate on the atomistic scale with molecular dynamics and on the continuum scale with a new simulation approach. The results indicated that high atomic/segmental mobility and low local density enabled the formation (nucleation) of highly deformed regions that grew to form plastic defects called plastic shear transformations. A continuum‐scale simulation was performed with the concept of plastic shear transformations as the basic region of deformation. The continuum simulations were able to predict the primary and secondary creep behavior. The slope of the secondary creep depended on the interactions between the plastic shear transformations. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 994‐1004, 2005

The Influence of Intrinsic Strain Softening on Strain Localization in Polycarbonate: Modeling and Experimental Validation

Intrinsic strain softening appears to be the main cause for the occurrence of plastic localization phenomena in deformation of glassy polymers. This is supported by the homogeneous plastic deformation behavior that is observed in polycarbonate samples that have been mechanically pretreated to remove (saturate) the strain softening effect. In this study, some experimental results are presented and a numerical analysis is performed simulating the effect of mechanical conditioning by cyclic torsion on the subsequent deformation of polycarbonate. To facilitate the numerical analysis of the “mechanical rejuvenation” effect, a previously developed model, the “compressible Leonov model,” is extended to describe the phenomenological aspects of the large strain mechanical behavior of glassy polymers. The model covers common observable features, like strain rate, temperature and pressure dependent yield, and the subsequent strain softening and strain-hardening phenomena. The model, as presented in this study, is purely “single mode” (i.e., only one relaxation time is involved), and therefore it is not possible to capture the nonlinear viscoelastic pre-yield behavior accurately. The attention is particularly focused on the large strain phenomena. From the simulations it becomes clear that the preconditioning treatment removes the intrinsic softening effect, which leads to a more stable mode of deformation. [S0094-4289(00)01002-1]

Experimental studies on the temperature fluctuations in deformed thermoplastics with defects

The temperature fluctuation during tensile testing of ABS (Acrylonitrile–Butadiene–Styrene), a typical thermoplastic copolymer with prefabricated defects, is experimentally studied in this paper. The initiation and evolution of the local temperature field near the defects are observed with infrared photography. It is shown that the specimen temperature decreases during the initial elastic deformation, whereas it rises in the following inelastic deformation process. According to the experiments, the heat generated from inelastic work is significant and approximates to 25–70 percent of the external work. Based on the microscopic and mesoscopic characteristics of deformation in glassy polymers, a preliminary and qualitative explanation of the cooling and heating phenomena is also presented.

Structural and Mechanical Behavior of Polymethylmethacrylate Containing Diethyl Siloxane Oligomer

Using the method of positron annihilation, structural changes induced by introduction of diethyl siloxane oligomers to PMMA were studied. The effect of these structural changes on the mechanical behavior of PMMA was discussed in terms of structural inhomogeneity of PMMA: existence of structural sublevels with different packing density and ordering. Deformation of glassy polymers at low strains as well as such mechanical characteristics as yield stress and contribution of low-temperature component to the temperature-induced relaxation of plastic deformation were shown to be controlled by segmental mobility in structural sublevels with a lower packing density.

Temperature-Induced Relaxation in Deformed Polymer Glasses

Temperature-induced relaxation of polymer glasses after their plastic deformation involves recovery of residual deformation and relaxation of inner energy stored by polymer during deformation. In general case, this process is realized in two temperature regions: at temperatures below polymer glass transition point and in temperature region of glass transition. Complex behavior of temperature-induced relaxation is considered in terms of specific features of elementary relaxation transitions and conformational changes in the deformed polymer as well as according to the speculations concerning supermolecular organization of polymer glasses. Principal approaches to the description of this phenomenon based on the examination of literature data are outlined. The importance of the research activities focused on temperature-induced relaxation of the deformed polymers is related to the development of modern theories of plastic deformation of glassy polymers.

Theory for the plastic deformation of glassy polymers

We present a theory to account for how a stress field can induce plastic flow in glassy polymers. We consider a molecular model in which chains are constituted from isotropic oriented elementary links embedded in a deforming continuum. The shear-stress field causes a redistribution of such links governed by a balance equation in orientation space. After detail calculations of the number of oriented units in certain directions, the net jump rate of the molecular links is given by an exponential form, according to the transition state theories of Adam and Gibbs [6]. These considerations are compared with the study of Boyce et al. [5] that included the effects of deformation rate, pressure and strain softening. The calculation of the plastic properties for polymethyl methacrylate and polycarbonate for various types of deformation has been made, and the corresponding results fitted the experimental data reasonably well.

Deformation in glassy polymers

Deformation in glassy polymers

Deformation in glassy polymers

On the basis of known nonlinearity of intermolecular force fields, we discuss the interpretation of PVT (pressure, volume, and temperature) behavior, pressure-temperature superposition for polymers, and the relationship between yield stress and tensile modulus. For PVT behavior of polymers, our theoretical results coincide with the experimental data, and their response to pressure is universal. The maximum theoretical yield strain, ϵy for glassy polymers is 1.08, and this value is beyond the elastic limit for glassy polymers. The previously established empirical relationship between yield stress, σy and tensile modulus, E: σy - 0.028 E, which again, is universal for glassy polymers, is predicted also by our phenomenological model. The theoretically predicted values of yield stress for glassy polymers range from 24 MPa to 84 MPa, coinciding with published experimental results. We discuss how the phenomenological model is helpful in the understanding of nonlinear viscoelasticity of glassy polymers © 1996 John Wiley & Sons, Inc.

Plastic deformation in glassy polymers by atomistic and mesoscopic simulations

We present here a short summary of two rather different, but complementary, simulations of plastic deformation in a flexible chain glassy polymer. In the first, atomistic simulation, a molecular structure model is used in which well‐established force fields between atoms and atom groups on a typical chain polymer are introduced to account for the most relevant molecular degrees of freedom that govern both structural and shear relaxations. The principal result of this simulation which has been described in great detail elsewhere [Mott et al., Philos. Mag. 67, 931–978 (1993a)] is that shear relaxations are in the form of abrupt shear transformations occurring in volume elements of ∼10 nm size and resulting in transformation shear strains of ∼2%. This simulation has established that the chemically specific conformational constraints are internal to the volume elements and that the interaction of the elements with their surroundings is elastic, suggesting that the phenomenon can be meaningfully simulated by a two‐dimensional mesoscopic model. In the second part of the present communication we summarize the most important findings of the extensive two‐dimensional mesoscopic simulation which we [Bulatov and Argon, Model. Sim. Mater. Sci. Eng. 2, 167–184 (1994a); 185–202 (1994b); 203–222 (1994c)] have performed. These findings include the important effects of disorder related misfit stresses in governing both quasihomogeneous flow at elevated temperatures and localized shear flow at lower temperatures. In addition, we demonstrate that these misfit stresses are the key ingredient that governs the initial deformation transients, as well as the well‐known distributed kinetics of the deformation process in amorphous media in general.

Work, heat and stored energy in compressive plastic deformation of glassy polymers

For a number of organic glassy polymers with different chemical structures and immiscible blends, the mechanical work expended for deformation, the plastic deformation heat and the internal energy stored in deformed samples (stored energy of cold work) have been measured using different experimental techniques. A comparison of the measured quantities is made and suggestions concerning their nature are discussed. It is found that the fraction of expended mechanical work transformed into stored internal energy upon deformation is very high for all studied systems. This reflects the non-isostructural character of inelastic deformation in glassy polymers. A two-stage deformation mechanism is introduced and the experimental results are analyzed in a framework of the suggested mechanism.

Mechanisms of plastic deformation in poly(diethylene glycol bis(allyl carbonate))

The plastic deformation of a highly crosslinked glassy polymer, poly(diethylene glycol bis(allyl carbonate)) (ADC resin) at different temperatures was investigated. It is found that both compressive yield stress σ y and Young's modulus E decrease as temperature is increased. The relationship between σ y and E has been analysed using Argon's and Bowden's theories of plastic deformation in glassy polymers. Molecular parameters derived from each theory have been discussed in terms of the chemical structure of the resin.

Relaxation and Deformation in Glassy Polymers

ABSTRACTA unified account of the structural relaxation and nonlinear deformation in glassy polymers is presented. The glassy state relaxation is derived from the local configurational rearrangements of molecular segments, and the dynamics of hole motion. We then apply this to predict the nonlinear stress-strain relationships.

Inelastic deformation of glassy polymers under creep conditions

Inelastic deformation of glassy polymers under creep conditions