Necking in glassy polymers: Effects of intrinsic anisotropy and structural evolution kinetics in their viscoplastic flow

Li, H.X.; Buckley, C. P.

doi:10.1016/j.ijplas.2010.02.004

Cited by 45 publications

(17 citation statements)

References 40 publications

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“…Once this level of strain was reached, the fibrillar state had developed fully in the central part of the specimen and was characterized by a maximum (final) value of an anisotropy index. This also complies with the apt term ''orientation hardening'' as used to qualify the strain hardening of polymers by Li and Buckley (2010).…”

Section: Discussionsupporting

confidence: 65%

“…The initial objective of this study was to gather a wide range of experimental results that could be advantageously used in further FE simulations to test models with respect to the propagation of plastic instabilities (Li and Buckley, 2010). In benchmark problems dealing with necking, FE simulations are generally compared with global macroscopic observables (stress-strain curves, radius evolution at the necking section of a circular bar, flow stress level during the neck propagation.…”

Section: Introductionmentioning

confidence: 99%

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Kinematic study of necking in a semi-crystalline polymer through 3D Digital Image Correlation

Silva

Farge

2015

International Journal of Solids and Structures

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a b s t r a c tThis study is devoted to the necking phenomenon and to the kinematic aspects associated with this plastic instability. The material studied is a High Density PolyEthylene deformed in tension. Full-field 3D-DIC (Digital Image Correlation) strain measurements were carried out on one face of a tensile specimen. On the opposite face, the longitudinal strain was measured in the central section using video-traction Ò , an extensometer based on marker tracking. This last measurement was used with feedback to control the strain rate in the specimen center. Specific data processing was run on the 3D-DIC measurements to obtain strain and strain rate maps up to true strain levels greater than 1.8. Even with measurements made on a relatively small strain rate range (smaller than 1 decade), we highlighted how much the necking phenomenon depends on the strain rate. In particular, we found that, around the yield point, the strain localization is more pronounced with higher strain rates. By analyzing the evolution of the strain rates in the necking shoulder regions, we carried out direct and original measurements of the strain level corresponding to the onset of necking stabilization (Natural Draw Ratio). This was possible because our original experimental protocol enabled us to obtain such strain maps even when the true strain values were significantly greater than 1. From an experimental point of view, we found that a video-extensometer based on marker tracking cannot efficiently measure the strain rate in the specimen center at large strain levels when the markers are greatly very deformed. In addition, a wide range of new experimental results (2D and 1D strain-rate and velocity data) is presented in this paper and we consider that this data should be particularly useful for the validation of numerical simulations of necking in polymers.

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Section: Discussionsupporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Kinematic study of necking in a semi-crystalline polymer through 3D Digital Image Correlation

Silva

Farge

2015

International Journal of Solids and Structures

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“…. This strain heterogeneity with the exact same trend has been shown by numerous authors and also using FE methods, when modelling plastic deformation processes of ductile materials (Mikkelsen, 1999;Li, 2010). As a result, when the X-ray beam travels along path A, it probes a strain larger than that "measured" at this time by DIC.…”

Section: I(q) Intensity Curvessupporting

confidence: 81%

Anisotropy development during HDPE necking studied at the microscale with in situ continuous 1D SAXS scans

Farge

Boisse

Bihannic

et al. 2017

J Polym Sci B Polym Phys

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Quantitative information about microstructural reorganizations which occur during mechanical solicitation is important to increase our knowledge on the rheology of semicrystalline polymers. This point is investigated here on High Density Polyethylene through the measurement of an anisotropy index calculated from small-angle X-ray scattering (SAXS) patterns. These were obtained in situ on a coherent synchrotron beamline with a very fast scanning of the specimen under tensile test. This allows the anisotropy development of many material points which undergo different deformation paths to be followed, thanks to necking development and propagation. With this field information, the microstructural anisotropy observable is shown to have a given value at a given true strain, meaning that strain pilots the bulk topology. Results apparently departing from that premise are shown indeed to be an experimental artifact: true strains are measured on the specimen surface, necking introduces strain heterogeneities in thickness, and the SAXS technique probes the full volume producing averaging.

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“…18, especially at large strain. It is believed that more detailed consideration of the interaction between matrix and inclusions and a more realistic anisotropic flow model could be able to achieve a better agreement [63]. (4) The structural relaxation parameters x and ß are fitted to a stress-free, constant heating profile of the thermal deformation (Fig.…”

Section: Appendix Amentioning

confidence: 99%

Thermoviscoplastic Modeling and Testing of Shape Memory Polymer Based Self-Healing Syntactic Foam Programmed at Glassy Temperature

2011

Journal of Applied Mechanics

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Traditionally, programming of shape memory polymer (SMP) material requires initial heating above the glass transition temperature (Tg), subsequent cooling below Tg and removal of the applied load. Therefore, the shape fixity process is inconvenient for some applications. Most recently, a new and effective approach, which programs glass transition activated SMPs directly at temperatures well below Tg,was introduced by Li and Xu [2011, “Thermomechanical Behavior of Shape Memory Polymer Programmed at Glassy Temperature: Testing and Constitutive Modeling,” J. Mech. Phys. Solids, 59(6), pp. 1231–1250. The 1D compression programming below Tg and free shape recovery were extensively investigated both experimentally and analytically. The current work extends this study into a shape memory polymer based self-healing syntactic foam, which was found to be capable of self-sealing structural scale damage repeatedly, efficiently, and almost autonomously [Li and John, 2008, “A Self-Healing Smart Syntactic Foam Under Multiple Impacts,” Compos. Sci. Technol., 68(15–16), pp. 3337–3343.]. A structural-relaxation constitutive model featuring damage-allowable thermoviscoplasticity was then developed to predict the nonlinear shape memory behavior of the SMP based syntactic foam programmed at glassy temperatures. After validated by both 1D (compression) and 2D (compression in longitudinal direction and tension in transverse direction) tests, the constitutive model was used to evaluate the effects of several design parameters on the thermomechanical behavior of the SMP based syntactic foam. It is concluded that the model is a useful tool for designing and training this novel self-healing composite.

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Necking in glassy polymers: Effects of intrinsic anisotropy and structural evolution kinetics in their viscoplastic flow

Cited by 45 publications

References 40 publications

Kinematic study of necking in a semi-crystalline polymer through 3D Digital Image Correlation

Kinematic study of necking in a semi-crystalline polymer through 3D Digital Image Correlation

Anisotropy development during HDPE necking studied at the microscale with in situ continuous 1D SAXS scans

Thermoviscoplastic Modeling and Testing of Shape Memory Polymer Based Self-Healing Syntactic Foam Programmed at Glassy Temperature

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