Gang Feng - Academia.edu (original) (raw)

Papers by Gang Feng

Advanced Materials Interfaces, 2014

ACS applied materials & interfaces, Jan 23, 2014

One common approach to generate lightweight materials with high specific strength and stiffness i... more One common approach to generate lightweight materials with high specific strength and stiffness is the incorporation of stiff hollow microparticles (also known as bubbles or microballoons) into a polymeric matrix. The mechanical properties of these composites, also known as syntactic foams, greatly depend on those of the hollow microparticles. It is critical to precisely control the properties of these bubbles to fabricate lightweight materials that are suitable for specific applications. In this paper, we present a method to tailor the mechanical properties and response of highly monodisperse nanoparticle-shelled bubbles using thermal treatment. We characterize the mechanical properties of individual as-assembled bubbles as well as those of thermally treated ones using nanoindentation and quantitative in situ compression tests. As-assembled bubbles display inelastic response, whereas thermally treated bubbles behave elastically. We also show that the stiffness and strength of bubbl...

Journal of the Mechanics and Physics of Solids, 2006

$Research paper thumbnail of Indentation size effects in single crystal copper as revealed by synchrotron x-ray microdiffraction$

Journal of Applied Physics, 2008

For a Cu single crystal, we find that indentation hardness increases with decreasing indentation ... more For a Cu single crystal, we find that indentation hardness increases with decreasing indentation depth, a phenomenon widely observed before and called the indentation size effect (ISE). To understand the underlying mechanism, we measure the lattice rotations in indentations of different sizes using white beam x-ray microdiffraction (μXRD); the indentation-induced lattice rotations are directly measured by the streaking of x-ray Laue spots associated with the indentations. The magnitude of the lattice rotations is found to be independent of indentation size, which is consistent with the basic tenets of the ISE model. Using the μXRD data together with an ISE model, we can estimate the effective radius of the indentation plastic zone, and the estimate is consistent with the value predicted by a finite element analysis. Using these results, an estimate of the average dislocation densities within the plastic zones has been made; the findings are consistent with the ISE arising from a dep...

Proquest Dissertations and Theses Thesis Stanford University 2006 Publication Number Aai3197428 Isbn 9780542431258 Source Dissertation Abstracts International Volume 66 11 Section B Page 6210 114 P, 2006

Carbon, 2013

ABSTRACT One of the few remaining opportunities to increase heat dissipation in IC circuitry is t... more ABSTRACT One of the few remaining opportunities to increase heat dissipation in IC circuitry is to sub-stantially decrease the thermal interface resistance between solid–solid contacts from source to sink. In this study, heterogeneous nanostructured mats (1–100 lm thick, ran-domly oriented networks of nanostructures) are synthesized for use as thermal interface materials (TIMs). Recent studies suggest that mats composed entirely of carbon nanotubes (CNTs) or graphite nanofibers (GNFs) can act as thermal insulators due to significant pho-non scattering at interfaces. In this work, graphene nanoplatelets (xGnPs) with high surface areas are included in CNT and GNF mats in order to increase the contact area between nanostructures and mitigate phonon scattering. Results indicate that an increase in con-tact area between nanostructures increases the thermal conductance across nanostructure networks by nearly an order of magnitude. Additionally, a study of the surface topography of CNT and GNF mats using atomic force microscopy (AFM) indicates that they are able to conform well to the asperities between rough, mating surfaces. Thus, an increase in con-tact area between CNT junctions not only produces a thermally conductive network, but also increases the reliability of a CNT mat TIM by avoiding common issues associated with the use of wetting agents.

Applied Physics Letters, 2013

The size-dependent plasticity of body centered cubic (bcc) metals is different from face centered... more The size-dependent plasticity of body centered cubic (bcc) metals is different from face centered cubic (fcc) metals: the size-effect exponent n varies for different bcc metal nanopillars (n = 0.8–1.0 for V, Nb; n = 0.3–0.5 for Ta, Mo, W). This inconsistency is first explained through a simple model based on the temperature-dependent Peierls stress. The bcc V nanopillars with a low critical temperature and Peierls stress showed a fcc-like size effect with n = 0.79, and our in-situ TEM compression study revealed that fcc-like dislocation starvation occurred in bcc V nanopillars, indicating that a small Peierls stress in V contributes to the fcc-like behavior.

Acta Materialia, 2007

The stress distribution outside the contact-induced plastic zone can be estimated by the superpos... more The stress distribution outside the contact-induced plastic zone can be estimated by the superposition of a Hertzian field and the field for an embedded center of dilatation (ECD) in a half-space, while the residual stress distribution can be estimated by the ECD field alone. This model has a simple closed-form analytical expression, matching with finite element results nearly perfectly.

Journal of Applied Physics, 2004

Obtaining quantitative electrical information with scanning probe microscopy techniques poses a s... more Obtaining quantitative electrical information with scanning probe microscopy techniques poses a significant challenge since the nature of the probe/sample contact is frequently unkown. For example, obtaining quantitative kinetic data from the recently developed atomic force microscopy (AFM) impedance technique requires normalization by the probe/sample contact area. In this paper, a methodology is proposed that enables the extraction of quantitative information from the AFM impedance technique. This methodology applies results from nanoindentation experiments and contact mechanics theory to characterize AFM probe contacts. Using these results, probe/sample contact forces (which can be accurately measured in the AFM) may be converted into probe/sample contact area estimates. These contact area estimates, when included in model of the probe/sample contact, enable the extraction of quantitative data. This methodology is applied to the recently developed AFM impedance measurement techni...