Inelastic Deformation and Fracture of Glassy Solids

Argon, A. S.

doi:10.21236/ada237290

Cited by 8 publications

(20 citation statements)

References 25 publications

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“…Plasticization of epoxy by the presence of water has been well-documented in the literature [49,50] Final proof of the culpability of water was obtained by thoroughly drying Nylon particles prior to their inclusion in model specimens; after postcuring the epoxy, no halos were observed around the particles. The most significant aspect of the plasticized halo regions is that their fracture toughness is approximately double that of the more fully cured epoxy.…”

Section: Analysis Of "Halos"mentioning

confidence: 99%

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Experimental investigations of crack trapping in brittle heterogeneous solids

Mower

Argon

1995

Mechanics of Materials

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Over the past two decades many mechanisms of toughening have been considered for brittle solids. Some of the most prominent ones applicable to either monolithic materials or fiberreinforced composites include deformation-induced local transformations, micro-cracking, crack trapping, crack bridging, and fiber pull-out. Few if any of these have been studied in the past in a manner which permitted evaluation of the effects of individual mechanisms in the absence of other interacting mechanisms. Here we present the development, analysis and results of an experimental study of toughening by the process of crack trapping by second-phase particles (spheres and fibers) of such toughness that make them impenetrable by probing cracks, forcing the cracks to bow around the obstacles with increasing applied load.The model fracture specimens employed here were wedge-loaded double cantilever beams cast of a brittle epoxy, containing macroscopic (3mm-diameter) inclusions of Nylon or polycarbonate having similar elastic properties to the matrix. The tests were performed at -60*C to achieve controlled, stable crack propagation. Images of the crack fronts advancing at velocities of about 10-4 M/s were recorded with good resolution, providing a continuous record of crack-front shapes during the evolution of the crack-trapping process from the initial pinning configuration through the transition to crack-flank bridging. Remarkable agreement between these images and crack-front shapes predicted by the numerical simulation of Bower & Ortiz is demonstrated. A parametric approach was adopted to study the influence of obstacle spacing, surface adhesion and thermally-induced residual stresses upon the observed crack-front behavior and enhanced stress intensity required to propagate the cracks past these obstacles. Analysis of the quantitative data has demonstrated that, in brittle matrices containing particle volume fractions of approximately 0.2, toughness enhancement by over a factor of two, relative to neat matrix values, may be achieved through the crack-trapping mechanism alone, provided that a high level of adhesion can be maintained between the matrix and the tough reinforcing particles.

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Section: Analysis Of "Halos"mentioning

confidence: 99%

“…The assumption of constant volume throughout each measurement is quite valid, since inelastic deformation processes in polymeric glasses are activated principally by deviatoric stress components (shear) [49,50], and the measurements were all performed at constant (atmospheric) pressure.…”

Section: A146 Reduction Of Datamentioning

confidence: 99%

Experimental investigations of crack trapping in brittle heterogeneous solids

Mower

Argon

1995

Mechanics of Materials

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“…Plastic deformation of glassy polymers is a topic of the intensive study now [1][2][3][4][5][6]. Two reasons, at least, are responsible for that.…”

Section: Introductionmentioning

confidence: 99%

“…This is true for any glassy solids. Different physical pictures of the process had been proposed for glassy polymers [2,4,6,[10][11][12][13][14]. However, choice between them is not easy and definite yet.…”

Section: Introductionmentioning

confidence: 99%

Energy Storage in Cold Non-elastic Deformation of Glassy Polymers

et al. 2006

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Experimental results on work W(ε), heat Q(ε) and stored energy U(ε) of deformation for glassy polymers such as linear PS, PC, PMMA, Polyimid, amorphous PET, thermotropic aromatic polyesters, Vectra™ for example, crosslinked epoxy are presented. All the data was obtained by a deformation calorimetry technique. Loading and unloading of samples were performed at room temperature with strain rate έ = 10-2 - 10-4 sec-1 under uniaxial compression up to engineering strains of εdef = 40-50%. During straining all polymers accumulate an excess of the latent energy U(ε). Elastic fraction of the energy is released completely at sample unloading and only residual Ures(ε) energy is conserved in samples. The latent energy Ures(ε) grows up to εdef =20-25% and levels off then. Shapes of the Ures(ε) curves are the same (S-shape) for all polymers. However, the saturation level is different for each polymer. The ratio U(ε)/W(ε) was also measured. It was found that at strains εdef < εy (εy - strain at the yield point) U(ε)/W(ε) ≈100%. I.e. all W is stored by sample in a form of U. The ratio decreases up to 60-30% for different polymers at higher strains. Release of the residual energy Ures (DSC measurements) and strain εres (thermally stimulated strain recovery technique) was measured for deformed and unloaded samples at heating. It was found that about 85-90% of Ures stored by samples is released in glassy state of polymers (below Tg). The Ures is related to a small fraction of εres, only to 7-10%. The rest of Ures and εres are recovered at the softening (devitrification) interval, around Tg. Computer modeling (molecular dynamics) of an isothermal shear deformation was performed for 2-dimentional two component atomic glass containing 500 Lennard-Jones particles of two different diameters. It was found that localized deformation events are of anelastic nature. The εan appears at early deformation stage in a form of localized shear events (transformations). Such events are nucleated in a sample and merged and united at later deformation stages, when concentration of the events becomes high enough. Finally, merged transformations form kind of shear band crossing entire sample. On the basis of experimental data and computer modeling the deformation mechanism for glassy polymers is proposed. The first stage of the process is the nucleation of “the carriers of non-elastic strain”, anelastic shear transformations (ASTs). All these ASTs are energetically excited. The concentration of the ASTs is responsible for the amount of Ures(ε) stored by a sample. It is suggested that such nucleation is the rate-controlling step in non-elastic deformation of any non-covalent glass. Saturation of the stored energy is defined by the reaching the steady state regime in carrier’s concentration. In this regime the rates of nucleation and termination (decrease of the stored local energy by AST) of carriers becomes equal. The termination proceeds spontaneously and easy (fast). The decrease of local energy of ASTs follows by local uncoiling of chains and by an appearance of new, extended chain conformers. However, such uncoiling is not the rate-controlling step for entire deformation process. Suggested mechanism very well describes all existing experimental facts. Deformation mechanisms for glasses seriously differ from that operating in rubbers and crystals.

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“…2 Therefore, the rate of plastic deformation in glassy polymers is controlled by the nucleation of shear transformations, rather than by their mobility. 2,11 A key parameter for understanding the plasticity in glassy solids at a molecular level is the size of the regions in which the shear transformations occur. For polymer glasses, the length scale of these plastic shear zones (PSZs) 2 is unknown, as are the molecular parameters that control it.…”

Section: Introductionmentioning

confidence: 99%

Plastic Deformation of Glassy Polymers: Correlation Between Shear Activation Volume and Entanglement Density

Govaert

Utz

2002

MRS Proc.

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The shear activation volumes of miscible polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) (PS-PPO) blends at different PS-PPO ratios were determined experimentally by both plane strain and uniaxial compression at constant strain rates. We find that the same correlation between the shear activation volume and the entanglement density ρe holds for the blend as well as for various pure glassy polymers: . Since the shear activation volume is closely related to the size of the plastic shear zones, this correlation suggests that the cooperativity of the elementary processes of plastic deformation in glassy polymers scales with the entanglement density.

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Inelastic Deformation and Fracture of Glassy Solids

Cited by 8 publications

References 25 publications

Experimental investigations of crack trapping in brittle heterogeneous solids

Experimental investigations of crack trapping in brittle heterogeneous solids

Energy Storage in Cold Non-elastic Deformation of Glassy Polymers

Plastic Deformation of Glassy Polymers: Correlation Between Shear Activation Volume and Entanglement Density

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