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Sha, Ye; Hui, Chung‐Yuen; Krämer, Edward J.

doi:10.1023/a:1004607523161

Cited by 13 publications

(5 citation statements)

References 13 publications

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“…More recently, Sha et al [53] pointed out the necessity of using a ratedependent drawing stress σ c as reported in [29,30]. If only this depen-dence is included in Brown's model, the toughness in Eq.…”

Section: Craze Breakdownmentioning

confidence: 99%

“…Therefore, Sha et al [53] incorporated a rate-dependent critical craze thickness in order to capture the evolution of the toughness with crack velocity. However, the evolution of the critical craze thickness predicted in [53] decreases by a factor of five from low to fast crack velocities which is not fully consistent with experimental observations [29,30], thus indicating that the process of craze fibril breakdown needs to be further clarified.…”

Section: Craze Breakdownmentioning

confidence: 99%

“…As the craze microstructure is intrinsically discrete rather than continuous, the connection between the variables in the cohesive surface model and molecular characteristics, such as molecular weight, entanglement density or, in more general terms, molecular mobility, is expected to emerge from discrete analyses like the spring network model in [52,53] or from molecular dynamics as in [49,50]. Such a connection is currently under development between the critical craze thickness and the characteristics of the fibril structure, and similar developments are expected for the description of the craze kinetics on the basis of molecular dynamics calculations.…”

Section: Conclusion and Future Trendsmentioning

confidence: 99%

See 2 more Smart Citations

Modeling and Computational Analysis of Fracture of Glassy Polymers

Estevez

Giessen

2005

Intrinsic Molecular Mobility and Toughness of Polymers II

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Section: Craze Breakdownmentioning

confidence: 99%

Section: Craze Breakdownmentioning

confidence: 99%

Section: Conclusion and Future Trendsmentioning

confidence: 99%

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Modeling and Computational Analysis of Fracture of Glassy Polymers

Estevez

Giessen

2005

Intrinsic Molecular Mobility and Toughness of Polymers II

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“…Denoting the theoretical maximum chain extension λ max between entanglements as λ max = L normale / l ent = l ent / l normalK ≡ n normale where L e is the chain contour length of an entanglement strand, l K is the Kuhn length, and n e is the number of Kuhn segments in an entanglement strand, Kramer and co-workers observed that brittle polymer glasses tend to have a larger λ max . Their extensive investigations − ,− on the characteristics of craze indicated that the extension in the craze zone, λ craze , is lower for a polymer with lower λ max . They further noted that the tensile stress σ fib exerted on fibrils in the craze is enhanced by a factor of λ craze relative to the applied tensile stress S , i.e., σ fib = λ craze S .…”

Section: Introductionmentioning

confidence: 99%

How Melt-Stretching Affects Mechanical Behavior of Polymer Glasses

et al. 2012

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This work takes a simple phenomenological approach to the questions of when, how, and why a brittle polymer glass turns ductile and vice versa. Perceiving a polymer glass as a hybrid, we recognize that both the primary structure formed by van der Waals forces (network 1) and chain network (i.e., the vitrified entanglement network) (network 2) must be accounted for in any discussion of the mechanical responses. To show the benefit of this viewpoint, we first carried out well-defined melt-stretching experiments on four common polymer glasses (PS, PMMA, SAN, and PC) in a systematic way either at a fixed Hencky strain rate to a given degree of stretching at several temperatures or at a given temperature to different levels of stretching using the same Hencky rate. Then we attempted to preserve the effect of melt-stretching on the chain network structure by rapid thermal quenching. Subsequent room-temperature tensile extension of these melt-stretched amorphous polymers reveals something universal: (a) along the direction of the melt-stretching, the brittle glasses (PS, PMMA, and SAN) all become completely ductile; (b) perpendicular to the melt-stretching direction, the ductile glass (PC) becomes brittle at room temperature. We suggest that the transformations (from brittle to ductile or ductile to brittle) arise from either geometric condensation or dilation of load bearing strands in the chain network due to the melt-stretching. Regarding a polymer glass as a structural hybrid, we also explored two other cases where the ductile PC becomes brittle at room temperature: (1) upon aging near the glass transition temperature; (2) when blended with PC of sufficiently low molecular weight. These results indicate that (i) the strengthening of the primary structure by aging can raise the failure stress σ* to a level too high for the chain network to sustain and (ii) the PC blend becomes brittle upon weakening the chain network by dilution with short chains.

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“…For example, Rottler and Robbins use molecular dynamic simulations to simulate the molecular level processes during craze nucleation, widening, and eventual breakdown. , However, the largest volume accessible to atomistic simulations is limited to roughly 100 nm 3 . Continuum models have been used in attempts to simulate regions of crazing through the inclusion of either locally anisotropic spring networks , or special finite elements that are nonlinear and highly anisotropic . Such continuum models, however, involve a priori assumptions regarding the location and orientation of the crazes.…”

Section: Introductionmentioning

confidence: 99%

Micromechanical Simulation of the Deformation and Fracture of Polymer Blends

Buxton

Balazs

2004

Macromolecules

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We couple morphological studies of binary, immiscible blends with mechanical studies of deformation and fracture to determine the influence of the blend composition on the initiation and propagation of cracks in polymeric materials. The Cahn−Hilliard (CH) method is employed to simulate the structural evolution of the molten AB blend. We assume that the material undergoes a rapid quench to yield a solid whose microstructure is given by the CH approach. The output from these CH simulations serves as the input to a dynamic lattice spring model (LSM), a micromechanical model that consists of a three-dimensional network of springs, which connect regularly spaced mass points. Within the LSM, the A and B phases, as well as the interfacial regions, are assigned distinct spring constants, thereby allowing us to model a blend of a compliant and a stiff polymer. With the application of a tensile deformation, the heterogeneous microstructures give rise to complex local elastic fields. Using an energy-based fracture criterion, we selectively remove springs from this system and thereby simulate the initiation and propagation of cracks within the material. By varying the relative stiffness and toughness of the phases, we determine how these characteristics affect the growth of the cracks. We also consider systems where the interface between the different species is mechanically weak, and consequently, fracture occurs through the decohesion of the different polymer domains. In all the systems considered here, we find that “clustering effects”, which are due to interactions between neighboring domains, play a major role in dictating where incipient fracture occurs. Through these studies, we can correlate the complex morphologies within the blend to the mechanical performance of the solid materials.

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Untitled

Cited by 13 publications

References 13 publications

Modeling and Computational Analysis of Fracture of Glassy Polymers

Modeling and Computational Analysis of Fracture of Glassy Polymers

How Melt-Stretching Affects Mechanical Behavior of Polymer Glasses

Micromechanical Simulation of the Deformation and Fracture of Polymer Blends

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