Fracture and Fatigue in Graphene Nanocomposites Rafiee, Mohammed A.; Rafiee, Javad; Srivastava, Iti ...
Small (Weinheim an der Bergstrasse, Germany),
January 18, 2010, Letnik:
6, Številka:
2
Journal Article
Recenzirano
Graphene fillers are shown to be remarkably effective in suppressing crack propagation in epoxy polymers (see image). The graphene fillers show comparable increases in fracture toughness and fatigue ...crack propagation resistance to carbon nanotube, nanoparticle, and nanoclay additives at one to two orders of magnitude lower nanofiller weight fraction. This extraordinary property is related to deflection processes associated with the high‐aspect‐ratio sheet structure of graphene.
In this study, the mechanical properties of epoxy nanocomposites with graphene platelets, single-walled carbon nanotubes, and multi-walled carbon nanotube additives were compared at a nanofiller ...weight fraction of 0.1 ± 0.002%. The mechanical properties measured were the Young’s modulus, ultimate tensile strength, fracture toughness, fracture energy, and the material’s resistance to fatigue crack propagation. The results indicate that graphene platelets significantly out-perform carbon nanotube additives. The Young’s modulus of the graphene nanocomposite was ∼31% greater than the pristine epoxy as compared to ∼3% increase for single-walled carbon nanotubes. The tensile strength of the baseline epoxy was enhanced by ∼40% with graphene platelets compared to ∼14% improvement for multi-walled carbon nanotubes. The mode I fracture toughness of the nanocomposite with graphene platelets showed ∼53% increase over the epoxy compared to ∼20% improvement for multi-walled carbon nanotubes. The fatigue resistance results also showed significantly different trends. While the fatigue suppression response of nanotube/epoxy composites degrades dramatically as the stress intensity factor amplitude is increased, the reverse effect is seen for graphene-based nanocomposites. The superiority of graphene platelets over carbon nanotubes in terms of mechanical properties enhancement may be related to their high specific surface area, enhanced nanofiller−matrix adhesion/interlocking arising from their wrinkled (rough) surface, as well as the two-dimensional (planar) geometry of graphene platelets.
We report the synthesis and fatigue characterization of fiberglass/epoxy composites with various weight fractions of graphene platelets infiltrated into the epoxy resin as well as directly ...spray-coated on to the glass microfibers. Remarkably only ∼0.2% (with respect to the epoxy resin weight and ∼0.02% with respect to the entire laminate weight) of graphene additives enhanced the fatigue life of the composite in the flexural bending mode by up to 1200-fold. By contrast, under uniaxial tensile fatigue conditions, the graphene fillers resulted in ∼3−5-fold increase in fatigue life. The fatigue life increase (in the flexural bending mode) with graphene additives was ∼1−2 orders of magnitude superior to those obtained using carbon nanotubes. In situ ultrasound analysis of the nanocomposite during the cyclic fatigue test suggests that the graphene network toughens the fiberglass/epoxy-matrix interface and prevents the delamination/buckling of the glass microfibers under compressive stress. Such fatigue-resistant hierarchical materials show potential to improve the safety, reliability, and cost effectiveness of fiber-reinforced composites that are increasingly the material of choice in the aerospace, automotive, marine, sports, biomedical, and wind energy industries.
The liquid−solid phase change enthalpy, crystallization, and thermal conductivity of graphene/1-octadecanol (stearyl alcohol) composite, a nanostructured phase change material, was investigated as a ...function of graphene content. The thermal conductivity (κ) of the nanocomposite increased by nearly 2.5-fold (∼140% increase) upon ∼4% (by weight) graphene addition while the drop in the heat of fusion (i.e., storage capacity) was only ∼15.4%. The enhancement in thermal properties of 1-octadecanol obtained with the addition of graphene is markedly superior to the effect of other nanofillers such as silver nanowires and carbon nanotubes reported previously in the literature. Boosting the thermal conductivity of organic phase change materials without incurring a significant loss in the heat of fusion is one of the key issues in enabling their practical application as latent heat storage/release units for thermal management and thermal protection.
The heating of houses comprises a considerable share of the total energy consumption in many developed countries in temperate and colder climates. While most of the factors affecting space heating ...depend on individual choices (e.g. occupants’ behaviour, interior building design, heating system efficiency) that are difficult to influence through urban planning, spatial context of individual housing units is within the sphere of influence of planners. Yet the impact of spatial context has hitherto received limited research attention due to the lack of geospatial data and the massive computer processing required to capture the shape and surroundings of individual housing units.
Regression analysis was performed in this study to explain the yearly gas consumption of all individual housing units in the city of Amsterdam, the Netherlands. The analysis focused on the impact of spatial context variables at two complementary scales: housing unit and postal code level. State-of-the-art 3D Geographic Information System (GIS) techniques were applied for the efficient processing of massive 3D geospatial data for all buildings in the city. Two- and three-dimensional spatial context of individual housing units were described using spatial data processing routines that characterised building shape and its surroundings.
The local housing unit level results highlighted the benefits of compact, dense urban forms: denser neighbourhoods with less open space and buildings with higher numbers of housing units and less exposed perimeters have lower heating demand. Trees were found to limit energy consumption when they are located on the colder northwest side of building units. The more aggregate postal code level results showed the importance of demographic composition: (larger) households with children consume most energy. Size and age of the housing unit are important determinants of energy at both scale levels: older houses have a higher energy consumption, but a rebound effect was found for the newest dwellings.
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•3D data and GIS technology can be used to characterize built environment.•Individual housing unit and postcode level provide complementary results.•Housing unit area, height and exposed perimeter strongly affect household heat demand.•Multifamily dwellings and dense neighbourhoods reduce energy consumption.•A substantial rebound affect is found for new (post 2010) houses.
► We model a masonry stone arch composed of three-dimensional blocks. ► We use the Non-Smooth Contact Dynamics method framework. ► We examine the mechanical behaviour of this academic model. ► We ...model a geometrically complex stone bridge on the basis of in situ measurements. ► We analyze the mechanical behaviour of this bridge under diverse loading conditions.
The aim of this study is to investigate the effect of different types of static loadings on the mechanical behaviour of a standard arch bridge and a masonry stone bridge in real scale. The mechanical analyses are performed using the Non-Smooth Contact Dynamic method (NSCD) known as an implicit discrete element method. After a brief description of the NSCD method, the stability state analysis is carried out over a classic stone arch in order to demonstrate the efficiency of this numerical method to reveal the diverse collapse mechanisms happening in the masonry structures under several static loading conditions. For the analysis of a real masonry structure, the roman stone bridge of the Pont Julien in Vaucluse (South of France) is studied, based on site measurements, under an academic loading, to show the capacity of the method to take into account heterogeneous loading patterns.
Transverse motion instability of a submerged moored buoy Orszaghova, J; Wolgamot, H; Draper, S ...
Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences,
01/2019, Letnik:
475, Številka:
2221
Journal Article
Recenzirano
Odprti dostop
Wave energy converters and other offshore structures may exhibit instability, in which one mode of motion is excited parametrically by motion in another. Here, theoretical results for the transverse ...motion instability (large sway oscillations perpendicular to the incident wave direction) of a submerged wave energy converter buoy are compared to an extensive experimental dataset. The device is axi-symmetric (resembling a truncated vertical cylinder) and is taut-moored via a single tether. The system is approximately a damped elastic pendulum. Assuming linear hydrodynamics, but retaining nonlinear tether geometry, governing equations are derived in six degrees of freedom. The natural frequencies in surge/sway (the pendulum frequency), heave (the springing motion frequency) and pitch/roll are derived from the linearized equations. When terms of second order in the buoy motions are retained, the sway equation can be written as a Mathieu equation. Careful analysis of 80 regular wave tests reveals a good agreement with the predictions of sub-harmonic (period-doubling) sway instability using the Mathieu equation stability diagram. As wave energy converters operate in real seas, a large number of irregular wave runs is also analysed. The measurements broadly agree with a criterion (derived elsewhere) for determining the presence of the instability in irregular waves, which depends on the level of damping and the amount of parametric excitation at twice the natural frequency.
In this paper the dynamics of a submerged axi-symmetric wave energy converter are studied, through mathematical models and wave basin experiments. The device is disk-shaped and taut-moored via three ...inclined tethers which also act as a power take-off. We focus on parasitic yaw motion, which is excited parametrically due to coupling with heave. Assuming linear hydrodynamics throughout, but considering both linear and nonlinear tether geometry, governing equations are derived in 6 degrees of freedom (DOF). From the linearized equations, all motions, apart from yaw, are shown to be contributing to the overall power absorption. At higher orders, the yaw governing equation can be recast into a classical Mathieu equation (linear in yaw), or a nonlinear Mathieu equation with cubic damping and stiffness terms. The well-known stability diagram for the classical Mathieu equation allows prediction of onset/occurrence of yaw instability. From the nonlinear Mathieu equation, we develop an approximate analytical solution for the amplitude of the unstable motions. Comparison with regular wave experiments confirms the utility of both models for making relevant predictions. Additionally, irregular wave tests are analysed whereby yaw instability is successfully correlated to the amount of parametric excitation and linear damping. This study demonstrates the importance of considering all modes of motion in design, not just the power-producing ones. Our simplified 1 DOF yaw model provides fundamental understanding of the presence and severity of the instability. The methodology could be applied to other wave-activated devices.
Many dental procedures are considered aerosol-generating procedures that may put the dental operator and patients at risk for cross-infection due to contamination from nasal secretions and saliva. ...This aerosol, depending on the size of the particles, may stay suspended in the air for hours. The primary objective of the study was to characterize the size and concentrations of particles emitted from 7 different dental procedures, as well as estimate the contribution of the nasal and salivary fluids of the patient to the microbiota in the emitted bioaerosol. This cross-sectional study was conducted in an open-concept dental clinic with multiple operators at the same time. Particle size characterization and mass and particle concentrations were done by using 2 direct reading instruments: Dust-Trak DRX (Model 8534) and optical particle sizer (Model 3330). Active bioaerosol sampling was done before and during procedures. Bayesian modeling (SourceTracker2) of long-reads of the 16S ribosomal DNA was used to estimate the contribution of the patients’ nasal and salivary fluids to the bioaerosol. Aerosols in most dental procedures were sub-PM1 dominant. Orthodontic debonding and denture adjustment consistently demonstrated more particles in the PM1, PM2.5, PM4, and PM10 ranges. The microbiota in bioaerosol samples were significantly different from saliva and nasal samples in both membership and abundance (P < 0.05) but not different from preoperative ambient air samples. A median of 80.15% of operator exposure was attributable to sources other than the patients’ salivary or nasal fluids. Median operator’s exposure from patients’ fluids ranged from 1.45% to 2.75%. Corridor microbiota showed more patients’ nasal bioaerosols than oral bioaerosols. High-volume saliva ejector and saliva ejector were effective in reducing bioaerosol escape. Patient nasal and salivary fluids are minor contributors to the operator’s bioaerosol exposure, which has important implications for COVID-19. Control of bioaerosolization of nasal fluids warrants further investigation.
Graphene–aluminum nanocomposites Bartolucci, Stephen F.; Paras, Joseph; Rafiee, Mohammad A. ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
10/2011, Letnik:
528, Številka:
27
Journal Article
Recenzirano
► We investigated the mechanical properties of aluminum and aluminum nanocomposites. ► Graphene composite had lower strength and hardness compared to nanotube reinforcement. ► Processing causes ...aluminum carbide formation at graphene defects. ► The carbides in between grains is a source of weakness and lowers tensile strength.
Composites of graphene platelets and powdered aluminum were made using ball milling, hot isostatic pressing and extrusion. The mechanical properties and microstructure were studied using hardness and tensile tests, as well as electron microscopy, X-ray diffraction and differential scanning calorimetry. Compared to the pure aluminum and multi-walled carbon nanotube composites, the graphene–aluminum composite showed decreased strength and hardness. This is explained in the context of enhanced aluminum carbide formation with the graphene filler.
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