Craze structure and stability in oriented polystyrene

Maestrini, C.; Krämer, Edward J.

doi:10.1016/0032-3861(91)90472-u

Cited by 33 publications

(19 citation statements)

References 33 publications

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“…In a previous study of crazing in oriented PS, the present authors demonstrated experimentally that the increase in the stress required for craze formation relative to the isotropic, σ c − σ

_{c}^{iso}

is proportional to optical birefringence for a wide range of orientations 9. The justification for this proportionality is based on Maestrini and Kramer's postulate, that a back stress acts to increase the stress required for craze formation σ c relative to the isotropic σ

_{c}^{iso}

9.…”

Section: Toolboxmentioning

confidence: 61%

“…Frozen‐in molecular orientation is frequently an important consideration of any design, because its presence leads to anisotropy of many material properties of practical interest. Such anisotropy has been readily observed experimentally through measurable changes of Young's modulus,1, 2 yield stress,3–6 crazing stress,7–11 optical birefringence,1, 3, 8, 12–14 strain‐hardening modulus,4–6, 15, 16 rate of ageing,17 and fracture toughness 18–21…”

Section: Introductionmentioning

confidence: 99%

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A toolbox for parameter‐free predictions of solid‐state properties of monodisperse glassy polymers with frozen‐in molecular orientation

Focatiis

Buckley

2012

J Polym Sci B Polym Phys

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This study presents a toolbox for the prediction of birefringence and craze initiation stress in oriented monodisperse linear amorphous polymers. The toolbox is assembled from a previously proposed melt-solid constitutive model that provides the necessary residual stress components required for predictions of birefringence and craze initiation stress. The Likhtman-McLeish theory for linear rheology of entangled polymers is used to generate the low reduced frequency part of the linear viscoelastic spectrum, the only molar massdependent input parameter. All other parameters are obtained by experiment or from literature and can be considered material constants. Toolbox predictions are compared to new experimental data on two grades of linear monodisperse polystyrene (PS) of known molar mass but unknown rheology and to literature data. The toolbox is able to account for the role of molar mass on birefringence and craze initiation stress of PS subjected to supraentanglement orientation processes.

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_{c}^{iso}

_{c}^{iso}

9.…”

Section: Toolboxmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

A toolbox for parameter‐free predictions of solid‐state properties of monodisperse glassy polymers with frozen‐in molecular orientation

Focatiis

Buckley

2012

J Polym Sci B Polym Phys

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“…Ductile/brittle microlaminates are manufactured by co-extruding the ductile and brittle glassy polymeric constituents to form tens to thousands of layers, resulting in some level of molecular orientation in the direction of co-extrusion. Beardmore and Rabinowitz (1975) and Maestrini and Kramer (1991) have noted, respectively, for glassy polymers PMMA and PS, that resistance to craze initiation Fig. 9.…”

Section: Materials Properties For Crazingmentioning

confidence: 99%

“…• It is well known that crazing is sensitive to network orientation (Beardmore and Rabinowitz, 1975;Maestrini and Kramer, 1991). Ductile/brittle microlaminates are manufactured by co-extruding the ductile and brittle glassy polymeric constituents to form tens to thousands of layers, resulting in some level of molecular orientation in the direction of co-extrusion.…”

Section: Materials Properties For Crazingmentioning

confidence: 99%

“…(11) (see Table 2), compared to that of the PMMA homopolymer. For convenience, the values for material parameters Q, Y andŝ for PMMA microlayers are kept identical to those for PMMA homopolymer.The expected increased craze flow stress (due to network orientation) (Maestrini and Kramer, 1991) in PMMA microlayers is modeled by decreasing the value ofâv 0 in Eq. (14) compared to PMMA homopolymer.…”

Section: Materials Properties For Crazingmentioning

confidence: 99%

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Micromechanics of toughening in ductile/brittle polymeric microlaminates: Effect of volume fraction

Sharma

Boyce

Socrate

2008

International Journal of Solids and Structures

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Ductile/brittle microlaminates, comprised of alternating layers of ductile polymer [e.g., polycarbonate (PC)] that inelastically deform by shear yielding, and brittle polymer [e.g., styrene-acrylonitrile (SAN), polymethylmethacrylate (PMMA)] that undergo crazing in tension, offer a strategy for tensile toughening by capitalizing on the synergistic interactions between crazing and shear yielding. This work presents a micromechanical model for PC/PMMA ductile/brittle laminates that captures the constituent volume fraction dependence of the macroscopic behavior, as well as the underlying micro-mechanisms of deformation and tensile failure, in particular the synergy between crazing and shear yielding. The finite element implementation of the model considers both two-dimensional and three-dimensional representative volume elements (RVEs), and incorporates continuum-based physics-inspired descriptions of shear yielding and crazing, along with failure criteria for the ductile (PC) and brittle (PMMA) layers. The interface between the ductile and brittle layers is assumed to be perfectly bonded. The 3D RVE models successfully capture the macroscopic tensile stress-strain behavior of the ductile/brittle laminates at varying constituent volume fractions and the corresponding underlying micromechanisms of deformation and failure. The transition from brittle to ductile laminate behavior is in agreement with experimental data and is found to occur as the fraction of the ductile layer is increased to 0.60. The simulations reveal the brittle to ductile cross-over to be governed by the ability of the ductile layers to constrain the dilation and growth of crazes in the brittle layer. In particular, after the critical volume fraction of the ductile constituent is attained, surface edge crazes are inhibited from tunneling across the width of the specimen which then leads to reduced crazing/cracking and increased shear yielding. 2D RVE models are unable to adequately account for the deformation and toughness of PC/PMMA microlaminates as a function of the constituent volume fractions, as they neglect any distribution of inelastic events in the laminate-width (out-of-plane) direction.

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Structural Modifications to Polystyrene via Self-Assembling Molecules

Stendahl¹,

Zubarev

Arnold³

et al. 2005

Adv. Funct. Mater.

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We have previously reported that small quantities of self‐assembling molecules known as dendron rodcoils (DRCs) can be used as supramolecular additives to modify the properties of polystyrene (PS). These molecules spontaneously assemble into supramolecular nanoribbons that can be incorporated into bulk PS in such a way that the orientation of the polymer is significantly enhanced when mechanically drawn above the glass‐transition temperature. In the current study, we more closely evaluate the structural role of the DRC nanoribbons in PS by investigating the mechanical properties and deformation microstructures of polymers modified by self‐assembly. In comparision to PS homopolymer, PS containing small amounts (≤ 1.0 wt.‐%) of self‐assembling DRC molecules exhibit greater Charpy impact strengths in double‐notch four‐point bending and significantly greater elongations to failure in uniaxial tension at 250 % prestrain. Although the DRC‐modified polymer shows significantly smaller elongations to failure at 1000 % prestrain, both low‐ and high‐prestrain specimens maintain tensile strengths that are comparable to those of the homopolymer. The improved toughness and ductility of DRC‐modified PS appears to be related to the increased stress whitening and craze density that was observed near fracture surfaces. However, the mechanism by which the self‐assembling DRC molecules toughen PS is different from that of conventional additives. These molecules assemble into supramolecular nanoribbons that enhance polymer orientation, which in turn modifies crazing patterns and improves impact strength and ductility.

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Craze structure and stability in oriented polystyrene

Cited by 33 publications

References 33 publications

A toolbox for parameter‐free predictions of solid‐state properties of monodisperse glassy polymers with frozen‐in molecular orientation

A toolbox for parameter‐free predictions of solid‐state properties of monodisperse glassy polymers with frozen‐in molecular orientation

Micromechanics of toughening in ductile/brittle polymeric microlaminates: Effect of volume fraction

Structural Modifications to Polystyrene via Self-Assembling Molecules

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