Lu, Hongbing

Permanent URI for this collectionhttps://hdl.handle.net/10735.1/2914

Professor Hongbing Lu is the Associate Head of the Department of Mechanical Engineering and holder of the Louis Beecherl Jr. Chair. Dr. Lu's research is in fundamental areas of mechanics such as the mechanics of time-dependent materials, dynamic behavior of materials, mechanical behavior of nanomaterials and fracture mechanics.

Learn more about Professor Lu on his Profile and Research Explorer pages.

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Recent Submissions

Now showing 1 - 8 of 8
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    Chemically Modified Graphene Films with Tunable Negative Poisson’s Ratios
    (Nature Publishing Group, 2019-06-04) Wen, Y.; Gao, E.; Hu, Zhenxing; Xu, Tingge; Lu, Hongbing; Xu, Z.; Li, C.; Hu, Zhenxing; Xu, Tingge; Lu, Hongbing
    Graphene-derived macroscopic assemblies feature hierarchical nano- and microstructures that provide numerous routes for surface and interfacial functionalization achieving unconventional material properties. We report that the microstructural hierarchy of pristine chemically modified graphene films, featuring wrinkles, delamination of close-packed laminates, their ordered and disordered stacks, renders remarkable negative Poisson’s ratios ranging from −0.25 to −0.55. The mechanism proposed is validated by the experimental characterization and theoretical analysis. Based on the understanding of microstructural origins, pre-strech is applied to endow chemically modified graphene films with controlled negative Poisson’s ratios. Modulating the wavy textures of the inter-connected network of close-packed laminates in the chemically modified graphene films also yields finely-tuned negative Poisson’s ratios. These findings offer the key insights into rational design of films constructed from two-dimensional materials with negative Poisson’s ratios and mechanomutable performance. © 2019, The Author(s).
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    A Multiscale Model to Study the Enhancement in the Compressive Strength of Multi-Walled CNT Sheet Overwrapped Carbon Fiber Composites
    (Elsevier Ltd) Ravindranath, P. K.; Roy, S.; Unnikrishnan, V.; Wang, X.; Xu, Tingge; Baughman, Ray H.; Lu, Hongbing; 0000-0001-5845-5137 (Baughman, RH); Xu, Tingge; Baughman, Ray H.; Lu, Hongbing
    The high tensile strength of polymer matrix composites is derived primarily from the high strength of the carbon fibers embedded in the polymer matrix. However, their compressive strength is generally much lower due to the fact that under compression, the fibers tend to fail through micro-buckling well before compressive fracture occurs. In this work, we consider multi-walled carbon nanotube (MWNT) sheets wrapped around carbon fiber at room temperature to improve fiber/matrix interfacial properties which, in turn, influences compressive strength of the composite. To investigate the effect of the wrapping of MWNT sheet on composite strength, Molecular Dynamics simulations were performed on an atomistic model of the interface region between the epoxy, carbon fiber and the scrolled MWNT sheets. The compressive strength of the unidirectional composite was computed using a novel hierarchical multi-scale model comprising of the rule of mixtures at the microscale, and the modified Argon's formula for composites at the macroscale. Model predictions were benchmarked through comparison with experimental data for different volume fractions of MWNT sheet. ©2019 Elsevier Ltd
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    Scalable, Hydrophobic and Highly-Stretchable Poly(Isocyanurate-Urethane) Aerogels
    (Royal Society of Chemistry) Malakooti, Sadeq; Rostami, Saman; Churu, H. G.; Luo, Huiyang; Clark, Jenna; Casarez, Fabiola; Rettenmaier, Owen; Daryadel, Soheil; Minary-Jolandan, Majid; Sotiriou-Leventis, C.; Leventis, N.; Lu, Hongbing; Malakooti, Sadeq; Rostami, Saman; Luo, Huiyang; Clark, Jenna; Casarez, Fabiola; Rettenmaier, Owen; Daryadel, Soheil; Minary-Jolandan, Majid; Lu, Hongbing
    Scalable, low-density and flexible aerogels offer a unique combination of excellent mechanical properties and scalable manufacturability. Herein, we report the fabrication of a family of low-density, ambient-dried and hydrophobic poly(isocyanurate-urethane) aerogels derived from a triisocyanate precursor. The bulk densities ranged from 0.28 to 0.37 g cm⁻³ with porosities above 70% v/v. The aerogels exhibit a highly stretchable behavior with a rapid increase in the Young's modulus with bulk density (slope of log-log plot > 6.0). In addition, the aerogels are very compressible (more than 80% compressive strain) with high shape recovery rate (more than 80% recovery in 30 s). Under tension even at high strains (e.g., more than 100% tensile strain), the aerogels at lower densities do not display a significant lateral contraction and have a Poisson's ratio of only 0.22. Under dynamic conditions, the properties (e.g., complex moduli and dynamic stress-strain curves) are highly frequency- and rate-dependent, particularly in the Hopkinson pressure bar experiment where in comparison with quasi-static compression results, the properties such as mechanical strength were three orders of magnitude stiffer. The attained outcome of this work supports a basis on the understanding of the fundamental mechanical behavior of a scalable organic aerogel with potential in engineering applications including damping, energy absorption, and substrates for flexible devices.
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    Structural, Elastic, Thermal, and Electronic Responses of Small-Molecule-Loaded Metal-Organic Framework Materials
    (Royal Soc Chemistry) Canepa, Pieremanuele; Tan, Kui; Du, Yingjie; Lu, Hongbing; Chabal, Yves J.; Thonhauser, Timo
    We combine infrared spectroscopy, nano-indentation measurements, and ab initio simulations to study the evolution of structural, elastic, thermal, and electronic responses of the metal-organic framework MOF-74-Zn when loaded with H-2, CO2, CH4, and H2O. We find that molecular adsorption in this MOF triggers remarkable responses in all these properties of the host material, with specific signatures for each of the guest molecules. With this comprehensive study, we are able to clarify and correlate the underlying mechanisms regulating these responses with changes of physical and chemical environments. Our findings suggest that metal-organic framework materials in general, and MOF-74-Zn in particular, can be very promising materials for novel transducers and sensor applications, including highly selective small-molecule detection in gas mixtures.
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    Luminescent LaF₃:Ce-Doped Organically Modified Nanoporous Silica Xerogels
    Yao, Mingzhen; Hall, Ryan; Chen, Wei; Mohite, Dhairyashil P.; Leventis, Nicholas; Lu, Ning; Wang, Jinguo; Kim, Moon J.; Luo, Huiyang; Lu, Hongbing
    Organically modified silica compounds (ORMOSILs) were synthesized by a sol-gel method from amine-functionalized 3-aminopropyl triethoxylsilane and tetramethylorthosilicate and were doped in situ with LaF3:Ce nanoparticles, which in turn were prepared either in water or in ethanol. Doped ORMOSILs display strong photoluminescence either by UV or X-ray excitation and maintain good transparency up to a loading level of 15.66% w/w. The TEM observations demonstrate that ORMOSILs remain nanoporous with pore diameters in the 5-10 nm range. LaF3:Ce nanoparticles doped into the ORMOSILs are rod-like, 5 nm in diameter and 10-15 nm in length. Compression testing indicates that the nanocomposites have very good strength, without significant lateral dilatation and buckling under quasi-static compression. LaF3:Ce nanoparticle-doped ORMOSILs have potential for applications in radiation detection and solid state lighting.
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    Fluorescent stereo microscopy for 3D surface profilometry and deformation mapping
    Hu, Zhenxing; Luo, Huiyang; Du, Yingjie; Lu, Hongbing
    Recently, mechanobiology has received increased attention. For investigation of biofilm and cellular tissue, measurements of the surface topography and deformation in real-time are a pre-requisite for understanding the growth mechanisms. In this paper, a novel three-dimensional (3D) fluorescent microscopic method for surface profilometry and deformation measurements is developed. In this technique a pair of cameras are connected to a binocular fluorescent microscope to acquire micrographs from two different viewing angles of a sample surface doped or sprayed with fluorescent microparticles. Digital image correlation technique is used to search for matching points in the pairing fluorescence micrographs. After calibration of the system, the 3D surface topography is reconstructed from the pair of planar images. When the deformed surface topography is compared with undeformed topography using fluorescent microparticles for movement tracking of individual material points, the full field deformation of the surface is determined. The technique is demonstrated on topography measurement of a biofilm, and also on surface deformation measurement of the biofilm during growth. The use of 3D imaging of the fluorescent microparticles eliminates the formation of bright parts in an image caused by specular reflections. The technique is appropriate for non-contact, full-field and real-time 3D surface profilometry and deformation measurements of materials and structures at the microscale.;
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    Polydicyclopentadiene Aerogels Grafted With PMMA: II. Nanoscopic Characterization and Origin of Macroscopic Deformation
    Mohite, Dhairyashil P.; Mahadik-Khanolkar, Shruti; Luo, Huiyang; Lu, Hongbing; Sotiriou-Leventis, Chariklia; Leventis, Nicholas
    Polydicyclopentadiene (pDCPD) is a polymer of emerging technological significance from separations to armor. It is a paradigm of ring opening metathesis polymerization (ROMP) and should be an ideal candidate for strong nanoporous solids (aerogels), however, excessive swelling of pDCPD wet-gels in toluene (up to 200% v/v), followed by de-swelling and severe deformation in acetone, renders the resulting aerogels unusable. With only 4-5% of the pendant cyclopentene double bonds of pDCPD engaged in crosslinking (see previous paper of this issue), introducing additional crosslinking with polymethylmethacrylate (PMMA) was deemed appropriate. Thus, even with an uptake of PMMA as low as 13% w/w, the resulting aerogels kept the shape and dimensions of their molds. Evidence though suggests (e.g., DSC) that PMMA remains a linear polymer, hence pDCPD/PMMA networks resist deformation, not because of molecular-level crosslinking, but due to a synergism related to the nanotopology of the two components. SEM and N-2 sorption on dry aerogels show that macroscopic deformation of wet-gels is accompanied by coalescence of nanoparticles. Small angle X-ray scattering (SAXS) shows that both deformed (pDCPD) and non-deformed (pDCPD/PMMA) aerogels consist of same-size primary particles (8-9 nm radius) that form non-mass-fractal secondary particles (21-27 nm radius). On the other hand, rheology shows that the pDCPD gel network is formed by mass fractal aggregates (D-f similar to 2.4). Putting this information together, it is concluded that the pDCPD network is formed by aggregates of secondary particles. It is suggested that particles coalescence is driven by non-covalent interactions that squeeze deformable secondary particles of one fractal assembly inside the empty space of another. As supported by skeletal density considerations, PMMA fills the space between primary particles; thus, secondary particles become rigid and can no longer squeeze past one another into the empty space of their higher fractal aggregates.
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    Polydicyclopentadiene Aerogels Grafted with PMMA: I. Molecular and Interparticle Crosslinking
    Mohite, Dhairyashil P.; Mahadik-Khanolkar, Shruti; Luo, Huiyang; Lu, Hongbing; Sotiriou-Leventis, Chariklia; Leventis, Nicholas
    Polydicyclopentadiene (pDCPD) is a polymer of emerging technological significance from separations to armor. It is a paradigm of ring opening metathesis polymerization (ROMP) and some of its remarkable properties (e. g., strength) have been attributed to crosslinking of the pendant cyclopentenes. pDCPD should be an ideal candidate for strong nanoporous solids (aerogels), however, excessive swelling of the wet-gels precursors in toluene (up to 200% v/v), followed by de-swelling and severe deformation in acetone, renders the resulting aerogels unusable. Based on spectroscopic evidence (IR, solid state C-13 NMR and several liquid H-1 NMR controls), only 4-5% of the pendant cyclopentene double bonds of pDCPD are engaged in crosslinking, via Wagener-type olefin coupling. Deformation was rectified via free radical polymerization of methylmethacrylate (MMA) in the pores of pDCPD wet-gels. The uptake of PMMA was varied in the 13-28% w/w range by varying the concentration of MMA. Evidence (e. g., differential scanning calorimetry) though suggests that PMMA remains a linear polymer, hence the pDCPD/PMMA network resist deformation, not because of molecular-level crosslinking, but due to a synergism related to the nano-topology of the two components (see next paper of this issue). With cylindrical monoliths available, the nature of the interparticle chemical bonding in pDCPD/PMMA aerogels was probed top-down with thermal conductivity and compression testing, using linear-polynorbornene (pNB) aerogels as a control system. The latter, with no pendant cyclopentenes, has no chance for interpolymer chain crosslinking. The solid thermal conduction and stiffness of pDCPD/PMMA and pNB aerogels scale similarly, pointing to a common mechanism for interparticle bonding. That was assigned to cross-metathesis, effectively extending the polymer chains of one nanoparticle into another, and was reflected on very high polydispersities (8-13).

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