Indentation into polymeric foams

Flores‐Johnson, E.A.; Li, Q.M.

doi:10.1016/j.ijsolstr.2010.03.025

Cited by 68 publications

(59 citation statements)

References 26 publications

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“…2(c) and 2(d)] are unique characteristics seen only in the intertwined VACNT systems. Neither foams, 40,41 where the deformation is confined only to regions directly beneath the indenter, nor noninteracting VACNTs, 42 where such shear would propagate without any microroller formation, show the unique features seen in Fig. 2.…”

Section: Resultsmentioning

confidence: 98%

“…46 The characteristics of flat-punch indentations into VACNT films closely resemble those reported for metallic 40,47 and polymeric foams. 41,46 In the spirit of foam-like deformation, the indentation zone for VACNTs is confined to the region directly beneath the indenter, while the surrounding regions are unaffected (see Fig. 2).…”

Section: F Comparing Indentation and Compressionmentioning

confidence: 99%

“…2,40,46 This is diametrically opposite to monolithic materials, where the plastic zone underneath the indenter tip is typically represented by a continuous hemispherical plastic zone. 39 Another common characteristic between indentation into conventional foams and VACNTs is the appearance of a so-called "tear line" 40,41 along the corner of the flat-punch indenter where the shear force is largest. The depth of this shear line in a foam generally depends on its strength.…”

Section: F Comparing Indentation and Compressionmentioning

confidence: 99%

“…The depth of this shear line in a foam generally depends on its strength. 40,41 Unlike foams, however, the constituents of the VACNT system-the individual CNTs themselves-are nominally vertically aligned with respect to the indenter tip [ Fig. 1(b)], and thus, the vertical plane is expected to be the plane of lowest shear strength in the VACNT matrix.…”

Section: F Comparing Indentation and Compressionmentioning

confidence: 99%

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Compressive response of vertically aligned carbon nanotube films gleaned from in situ flat-punch indentations

et al. 2012

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We report the mechanical behavior of vertically aligned carbon nanotube films, grown on Si substrates using atmospheric pressure chemical vapor deposition, subjected to in situ large displacement (up to 70 lm) flat-punch indentations. We observed three distinct regimes in their indentation stress-strain curves: (i) a short elastic regime, followed by (ii) a sudden instability, which resulted in a substantial rapid displacement burst manifested by an instantaneous vertical shearing of the material directly underneath the indenter tip by as much as 30 lm, and (iii) a positively sloped plateau for displacements between 10 and 70 lm. In situ nanomechanical indentation experiments revealed that the shear strain was accommodated by an array of coiled carbon nanotube "microrollers," providing a low-friction path for the vertical displacement. Mechanical response and concurrent deformation morphologies are discussed in the foam-like deformation framework with a particular emphasis on boundary conditions.

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Section: Resultsmentioning

confidence: 98%

Section: F Comparing Indentation and Compressionmentioning

confidence: 99%

Section: F Comparing Indentation and Compressionmentioning

confidence: 99%

Section: F Comparing Indentation and Compressionmentioning

confidence: 99%

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Compressive response of vertically aligned carbon nanotube films gleaned from in situ flat-punch indentations

et al. 2012

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“…Although experiments of quasi-static indentation and low velocity impact Rohacell 51 WF foam have been presented elsewhere [Flores-Johnson and Li (2010); (2011b)], a summary of the experimental details and results are presented in this Section as the numerical predictions in Section 3 are compared with the empirical data.…”

Section: Methodsmentioning

confidence: 99%

Numerical Simulations of Quasi-Static Indentation and Low Velocity Impact of Rohacell 51 Wf Foam

Flores‐Johnson

Shen

2014

Int. J. Comput. Methods

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Numerical simulations of quasi-static indentation and low velocity impact of low density polymethacrylimide (PMI) Rohacell 51WF foam using indenters with different nose shapes (conical, truncated-conical, hemi-spherical and flat) were carried out using finite element code LS-DYNA. A 2D axisymmetric model was generated. A strain-rate dependent material model and r-adaptive remeshing was used for low velocity impact simulations. Numerical predictions were compared with available experimental data with good agreement between numerical simulations and experiments. The results demonstrated the ability of the model to reproduce the mechanisms of deformation of the penetration process in quasi-static indentation and low velocity impact. The predicted resistance force closely matches the empirical results.

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Metasurface‐Enabled Holographic Lithography for Impact‐Absorbing Nanoarchitected Sheets

et al. 2023

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Nano-architected materials represent a class of structural meta-materials that utilze nanoscale features to achieve unconventional material properties such as ultra-low density and high energy absorption. A dearth of fabrication methods capable of producing architected materials with sub-micron resolution over large areas in a scalable manner exists. We present a fabrication technique that employs holographic patterns generated by laser exposure of phase metasurface masks in negative-tone photoresists to produce 30 to 40 micrometer thick nano-architected sheets with 2.1 x 2.4 cm 2 lateral dimensions and approximately 500 nm wide struts organized in layered 3D brick-and-mortar-like patterns to result in approximately 50 to 70% porosity. Nanoindentation arrays over the entire sample area reveal the out-of-plane elastic modulus to vary between 300 MPa and 4 GPa, with irrecoverable post-elastic material deformation commencing via individual nano-strut buckling, densification within layers, shearing along perturbation perimeter, and tensile cracking. Laser induced particle impact tests (LIPIT) indicate specific inelastic energy dissipation of 0.51-2.61 MJ kg -1 , which is comparable to other high-impact energy absorbing composites and nanomaterials, such as Kevlar/polyvinyl butyral (PVB) composite, polystyrene, and pyrolized carbon nanolattices with 23% relative density. These results demonstrate that holographic lithography offers a promising platform for scalable manufacturing of nano-architected materials with impact resistant capabilities.

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Indentation into polymeric foams

Cited by 68 publications

References 26 publications

Compressive response of vertically aligned carbon nanotube films gleaned from in situ flat-punch indentations

Compressive response of vertically aligned carbon nanotube films gleaned from in situ flat-punch indentations

Numerical Simulations of Quasi-Static Indentation and Low Velocity Impact of Rohacell 51 Wf Foam

Metasurface‐Enabled Holographic Lithography for Impact‐Absorbing Nanoarchitected Sheets

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