Nielsen Models Research Articles

Experimental investigation on duration of load effect of novel inorganic-bonded bamboo composite under flexural load

Conventional engineered wood and bamboo materials commonly require organic adhesives for adequate bonding. As an alternative solution in bio-based composites, a novel bamboo-based composite prepared with a magnesium-based inorganic adhesive was proposed herein, which is named as “inorganic-bonded bamboo composite” and abbreviated as InorgBam. This study investigates the duration of load (DOL) effect on InorgBam beams under long-term flexural load. The percentile matching method was used to obtain the short-term strengths matched to the long-term specimens, and the strength reduction of the long-term specimens was obtained. The DOL result were calibrated using the DOL empirical formulas and DOL damage models, including Gerhards, Foschi and Yao, and Nielsen models. The impact of the selected cumulative probability functions of short-term strength on the DOL analysis has also been discussed. Results illustrated that the strength reduction in the InorgBam was less than the prediction of Madison curve. The value of DOL coefficient determined with Foschi and Yao model was closest to that derived from the empirical fitted formula. The DOL effect of the InorgBam beams was significantly smaller than that of conventional engineered wood beams, which is beneficial for determining the design strength value of InorgBam material.

Re-Analysis of Historical Data and Model Calibration of Duration of Load Effect on Structural Timber

The duration of load (DOL) effect in structure timber refers to the degradation of strength and stiffness that occurs under long-term continuous loading. This paper investigated the DOL effect in structure timber using DOL tests and DOL damage models. Based on the empirical-fitted formulae, the DOL coefficients were derived for three long-term sustained loads in bending, tension perpendicular to grain, and shear parallel to grain, and the results were compared and analyzed with the Madison equation, Gerhards model, Nielsen model, and Foschi and Yao model derivations to verify the applicability of the DOL empirical model and the three DOL damage models. The results show that based on the historical data of the DOL tests, the Madison empirical formula was found to be better applied to the derivation of DOL coefficients under the bending and tension perpendicular to grain long-term sustained loading, and the derivation of DOL coefficients under shear loading is not satisfactory. Among the three DOL damage models, the Foschi and Yao model was better than the Gerhards and Nielsen models for fitting the DOL test results under bending, tension perpendicular to grain, and shear parallel to grain. The DOL coefficients derived based on the Foschi and Yao model are more comparable to test results and resemble those derived from the Madison formula.

Mechanical and Thermal Properties of Epoxy Polymer Composites Reinforced with CuO

Polymer nano composites using CuO as filler material and epoxy as matrix materials were prepared with different concentrations of CuO nano particles (1-5 wt%) by shear mixing followed by ultra-sonication process. The mechanical properties such as compressive strength and modulus were characterized using ASTM standards. It was found that the addition of CuO nano particles both compressive strength and modulus increased. As the CuO content increased in epoxy matrix the moduli values found to increase and were further analyzed using micromechanical models. The analytical models discussed correlate well with experimental values. The models discussed include Nicolais – Narkis, Turcsanyi, Piggot – Leidner and Nielsen models for the tensile strength values and for tensile modulus the models discussed include Halpin Tsai, Kerner and Sato – Furukawa models. These micromechanics models predict stiffness of nanocomposites with both aligned and randomly oriented fillers. XRD pattern revealed the interaction between CuO nanoparticles and epoxy matrix. The thermal decomposition behaviour revealed that there is an enhancement of onset of decomposition temperature by 28oC for 5wt% CuO filled epoxy than that of pure epoxy

Dynamic mechanical analysis of nylon 6 fiber-reinforced acrylonitrile butadiene rubber composites

Dynamic mechanical properties of polymeric materials are of direct relevance to a range of unique polymer applications. The aim of the study is to investigate the dynamic mechanical properties of composites of short nylon 6 fiber with acrylonitrile butadiene rubber (NBR). The storage modulus (G′), loss modulus (G″), and the damping factor (tan δ) have been analyzed with reference to the effects of fiber loading, curing systems, and bonding agents over a range of temperature and at varying frequencies. The storage modulus increases with increment in fiber loading, whereas loss modulus and damping factor decrease. The glass transition temperature shifts to higher temperature upon increment in fiber loading. Dicumyl peroxide (DCP)–cured composites show higher storage modulus and lower damping than the corresponding sulfur-cured one. The addition of hexa-resorcinol and phthalic anhydride as bonding agents enhances the dynamic mechanical properties of the composites. The experimental results have been evaluated by comparing with Einstein, Guth, and Nielsen models.

Oxygen Barrier Performance of Poly(vinyl alcohol) Coating Films with Different Induced Crystallinity and Model Predictions

The presence of the crystalline regions in poly(vinyl alcohol) coating films acts as barrier clusters forcing the gas molecules to diffuse in a longer pathway in the amorphous region of the polymer, where diffusivity and solubility are promoted in comparison. Evaluating the influence of crystalline regions on the oxygen barrier property of a semi-crystalline polymer is thus essential to prepare better coating films. Poly(vinyl alcohol) coating films with varying induced crystallinity were prepared on a polyethylene terephthalate (PET) substrate by drying at different annealing temperatures for 10 min. The coating films were first delaminated from the PET substrate and then characterized using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) techniques to determine and confirm the induced percentage of crystallinity. The barrier performance of the coating films, i.e., the oxygen transmission rate (OTR), was measured at room temperature. Results showed a decrease in the OTR values of poly(vinyl alcohol) film with an increase in the degree of crystallinity of the polymer matrix. Tortuosity-based models, i.e., modified Nielsen models, were adopted to predict the barrier property of the semi-crystalline PVOH film with uniform or randomly distributed crystallites. A modified Nielsen model for orderly distributed crystallites with an aspect ratio of 3.4 and for randomly distributed crystallites with an aspect ratio of 10.4 resulted in a good correlation with the experimental observation. For the randomly distributed crystallites, lower absolute average relative errors of 4.66, 4.45, and 5.79% were observed as compared to orderly distributed crystallites when the degree of crystallinity was obtained using FTIR, DSC, and XRD data, respectively.

Effects of Al2O3 on Thermal Conductivity of Silicone Rubber

Thermal conductivities of silicone rubber filled with Al2O3 were prepared. Thermal conductivity experimental results obtained were analyzed using the Nielsen and Agari models to explain the effect of Al2O3 filler on the formation of thermal conductive networks. Thermal conductivities increased with the adding of mixed Al2O3 of large and small sizes fillers. The scanning electron microscopy (SEM) showed that it is the optimum particle sizes and quantities that made the filler packing closer, which thus leads to formation of more thermal conductive chains.

Psychiatrists' Attitudes Toward Disruptive New Technologies: Mixed-Methods Study.

BackgroundRecent discoveries in the fields of machine learning (ML), Ecological Momentary Assessment (EMA), computerized adaptive testing (CAT), digital phenotype, imaging, and biomarkers have brought about a new paradigm shift in medicine.ObjectiveThe aim of this study was to explore psychiatrists’ perspectives on this paradigm through the prism of new clinical decision support systems (CDSSs). Our primary objective was to assess the acceptability of these new technologies. Our secondary objective was to characterize the factors affecting their acceptability.MethodsA sample of psychiatrists was recruited through a mailing list. Respondents completed a Web-based survey. A quantitative study with an original form of assessment involving the screenplay method was implemented involving 3 scenarios, each featuring 1 of the 3 support systems, namely, EMA and CAT, biosensors comprising a connected wristband-based digital phenotype, and an ML-based blood test or magnetic resonance imaging (MRI). We investigated 4 acceptability domains based on International Organization for Standardization and Nielsen models (usefulness, usability, reliability, and risk).ResultsWe recorded 515 observations. Regarding our primary objective, overall acceptability was moderate. MRI coupled with ML was considered to be the most useful system, and the connected wristband was considered the least. All the systems were described as risky (410/515, 79.6%). Regarding our secondary objective, acceptability was strongly influenced by socioepidemiological variables (professional culture), such as gender, age, and theoretical approach.ConclusionsThis is the first study to assess psychiatrists’ views on new CDSSs. Data revealed moderate acceptability, but our analysis shows that this is more the result of the lack of knowledge about these new technologies rather than a strong rejection. Furthermore, we found strong correspondences between acceptability profiles and professional culture profiles. Many medical, forensics, and ethical issues were raised, including therapeutic relationship, data security, data storage, and privacy risk. It is essential for psychiatrists to receive training and become involved in the development of new technologies.

Modeling of Gas Permeation through Mixed-Matrix Membranes Using Novel Computer Application MOT

The following article proposes a modern computer application MOT (Membrane Optimization Tool) for modeling of gas transport processes through mixed-matrix membranes (MMMs). The current version of the application is based on the Maxwell model, which can be successfully used to model gas transport through the simplest types of hybrid membranes without any defects. The application has been verified on the example of four types of hybrid membranes, consisting of various types of polymer matrix, such as: poly (vinyl acetate), 2, 2′-BAPB + BPADA, Ultem, hyperbranched polyimide (ODPA-MTA) and zeolite 4A. The average absolute relative error (AARE) and root-mean-square error (RMSE) were calculated in order to compare the theoretical MOT-predicted results with the experimental results. It was found that the AARE ranges from 29% to 36%, while the RMSE is in the range of 10% to 29%. The article presents also the comparison of MOT-predicted data obtained with Maxwell and Bruggeman models. To obtain more accurate reproduction of experimental results, further versions of the proposed application will be extended with next-generation permeation models (Lewis–Nielsen, Pal, modified Maxwell or Felske models), allowing for the description of transport in more complex systems with the possibility of taking into account possible defects.

Characterizing and Modeling of Mechanical Properties of Epoxy Polymer Composites Reinforced with Fly ash

This paper presents a critical review of the current experimental work and micro-mechanical numerical analysis of epoxy composites reinforced with fly ash. Polymer Matrix Composites (PMC’s) occupy a prime spot in the area of materials due to their lightweight and good mechanical strength. The most commonly used PMC’s are epoxy resins. The property of the epoxy resins can be improved by using fillers. Among the research going on in newer materials the modification of polymers by fillers has gained prominence. In the present work we have used fly ash as a filler material and its effect on tensile and compressive properties of Lapox L12 slabs by varying the fly ash loadingfrom0 to 20% in the epoxy matrix.The nanocomposites showed enhanced mechanical properties and was further analysed using micromechanical models. For the analysed polymer composite, both the tensile strength and modulus curves computed using the analytical model correlate well with experimental values. The models discussed include Nicolais – Narkis, Turcsanyi, Piggot – Leidner and Nielsen models for the tensile strength values and for tensile modulus the models discussed include Halpin Tsai, Kerner and Sato – Furukawa models. These micromechanics models predict stiffness of nanocomposites

Characterizing and Modeling of Mechanical Properties of Epoxy Polymer Composites Reinforced with Bentonite Clay

Polymer nano composites using clay as filler material and epoxy as matrix materials were prepared with different concentrations of clay nano particles (2.5-10 wt%) by shear mixing followed by ultra-sonication process. The mechanical properties such as compressive properties and tensile properties were characterized using ASTM standards. It was found that the addition of clay nano particles improved both compressive strength and tensile strength of pure epoxy significantly. As the clay content increased in epoxy matrix the moduli values found to increase and were further analyzed using micromechanical models. The analytical models discussed correlate well with experimental values. The models discussed include Nicolais – Narkis, Turcsanyi, Piggot – Leidner and Nielsen models for the tensile strength values and for tensile modulus the models discussed include Halpin Tsai, Kerner and Sato – Furukawa models. These micromechanics models predict stiffness of nanocomposites with both aligned and randomly oriented fillers. XRD pattern revealed the interaction between clay nanoparticles and epoxy matrix. The thermal decomposition behavior revealed that there is an enhancement of onset of decomposition temperature by 31°C for 10wt% clay filled epoxy than that of pure epoxy for 5% weight loss.

Improving oxygen barrier property of biaxially oriented PET/phosphate glass composite films

A new formulation of low glass transition temperature phosphate glass (Pglass) was developed to avoid degradation of, then melt blended with poly(ethylene terephthalate), (PET), in the presence of a sulfonated PET copolymer compatibilizer, providing an effective dispersion of the filler in polymer matrix. Compression molded films were then stretched to a draw ratio of 3 × 3 at the polymer glass transition temperature; scanning electron microscopy confirmed that the Pglass droplets successfully transformed into platelets with high aspect ratio under the processing condition. A 20-fold reduction in oxygen permeability was obtained with oriented 20 vol% Pglass in the PET matrix. The experiment data were fitted with the Nielsen and Cussler models to extract the platelet filler aspect ratios; the fitting result also indicated that the compatibilizer was effective in bringing Pglass and PET together. Enhanced the moduli and significantly reduced ductility, typical of filled systems, were observed in this family of materials.

Gas permeation and selectivity of poly(dimethylsiloxane)/graphene oxide composite elastomer membranes

The gas transport properties of graphene oxides (GO) incorporated into highly elastic poly(dimethylsiloxane) (PDMS)/GO elastomers synthesized from graphite and telechelic, amine-terminated PDMS were investigated. To develop broad fundamental understanding of the connection between composite architecture and gas transport properties, both gas barrier and separation characteristics were evaluated. The permeability for several common gases was studied as a function of GO concentration. Incorporating only 3.55vol% (8wt%) GO into the PDMS matrix resulted in a more than 99.9% reduction in gas permeation for various gases, such as H2, O2, N2, CH4 and CO2. Moreover, factor of two enhancements in gas selectivities were observed for CO2/N2 and CO2/CH4 compared to neat PDMS membranes. As a supplement to experimental data from scanning-electron and atomic-force microscopy and x-ray diffraction, theoretical models such as the Nielsen and Cussler models were applied to comprehend the dispersion and alignment of GO in the polymer.

Chitosan composites reinforced with nanostructured waste fly ash

This paper outlines the preparation and characterization of chitosan (CS) composites reinforced with mechano-chemically activated fly ash (MCA-FA). A series of composite films was prepared by solution casting method with varying filler content. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses showed good compatibility between the CS matrix and MCA-FA. The surface roughness and irregularity in shape of MCA-FA resulted in its efficient mechanical interlocking with the polymer matrix. This, in turn enhanced the mechanical properties of these composites. All the composite films exhibited a higher tensile strength and a lower percentage of elongation-at-break compared with the pure CS film. The highest tensile strength was observed for the composite films with 1 wt% of filler loading and the reduction in the tensile properties at higher filler loading was due to agglomeration of filler and polymer–filler interface debonding. The tensile strength data were analyzed using Nielsen and Pukanzsky models to understand the interface formation and polymer–filler interactions. Thermal properties showed a marginal improvement due to the incorporation of MCA-FA. Overall, this study indicates that MCA-FA could be used as value added filler in polymer matrix composites.

Effects of aluminium nitride silane-treatment on the mechanical and thermal properties of polybenzoxazine matrix

A new kind of polymer composite, produced from the typical polybenzoxazine and 0–30 wt-% native and silane-treated aluminium nitride (T-AlN), was investigated. The mechanical tests revealed a significant increase in the microhardness and flexural properties upon adding the T-AlN particles compared to that obtained from the untreated ones. By adding 0–30 wt-% T-AlN, the tensile moduli were accurately reproduced by the Halpin-Tsai and Nielsen models. At 30 wt-% T-AlN, dynamic mechanical analysis showed a significant increase in the storage moduli and the glass transition temperature (Tg), reaching 3.2 GPa and 217°C, respectively. The thermal stability of these materials was significantly improved upon the addition of the T-AlN fillers. These improvements are attributed to the high thermal and mechanical properties of the fillers and their good dispersion and adhesion in and to the matrix as revealed by a morphological analysis.

Production and characterisation of mechanical properties of Ti–Nb–Ta–Mn alloys foams for biomedical applications

Development of titanium foams with low Young’s modulus as a potential implant material has attracted significant attention. In this work, the effect of manganese on the mechanical properties in compression of Ti–13Ta–30Nb–xMn foams (x = 2–6 wt-%) has been studied. Titanium based alloys produced by mechanical alloying were processed to obtain foams using ammonium hydrogen carbonate with a mean particle size of 35 μm (50% v/v) as a space-holder. Powders and space-holder were mixed and uniaxially pressed to form compacts. The space holder was removed by heating the green compacts to 180°C for 1.5 h before sintering at 1300°C for 4 h in Ar. The Young’s modulus of the foam was lower than that of pure Ti, and the yield strength increased with the Mn addition. The Gibson–Ashby, Meyer and Nielsen models were applied to predict the mechanical properties of the titanium foams.

Polyethylene-based nanocomposites containing organoclay: A new approach to enhance gas barrier via multilayer coextrusion and interdiffusion

Layer multiplying coextrusion was employed to produce films consisting of alternating layers of unfilled and particulate filled polymers, i.e., low density polyethylene (LDPE) and maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA)/organoclay nanocomposites. Layer multiplying coextrusion was employed to produce gas barrier films consisting of alternating layers of unfilled and particulate filled polymers, i.e., low density polyethylene (LDPE) and maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA)/organoclay nanocomposite. To further enhance gas barrier performance, the clay concentration within the nanocomposite layers was increased several fold through annealing of the multilayer film in the melt state. Residing in the melt state activated the interdiffusion between the polymers and due to a significant difference in the molecular mobility between the LDPE and LLDPE-g-MA chains led to a moving boundary effect which contracted the (LLDPE-g-MA)-rich nanocomposite layers and expanded the LDPE-rich layers. Analysis of the clay morphology within the nanocomposite layers demonstrated an increase in the clay particle lengths and aspect ratios, which was attributed to the growth of “skewed” aggregates during layer contraction and particle concentration. The melt induced clay concentration and increased clay particle dimensions caused a significant decrease in oxygen permeability of the nanocomposite layers and reduced the overall permeability of the multilayered films. Morphology and transport behavior of the multilayered films were compared to a series of LLDPE-g-MA/clay bulk nanocomposites with varying clay content prepared by melt compounding in a twin screw extruder. Nielsen and Cussler models were used to describe the gas barrier data of the nanocomposite films. Although both models can be fit well to the experimental data, the Cussler model showed a better agreement with the morphological observations.

Rigorous calculations of permeation in mixed-matrix membranes: Evaluation of interfacial equilibrium effects and permeability-based models

We present rigorous calculations of single-component permeation in mixed-matrix membranes (MMMs), and show their importance in developing a more reliable understanding of MMM permeation behavior. We first develop methods for the construction of detailed and large-scale 3D mixed-matrix membrane (MMM) models, which are then solved by finite-element methods. Our models explicitly account for the effects of matrix-filler interfacial equilibrium in addition to the differences in Fickian diffusivity between the two phases. Analytical equations (e.g., Maxwell model) can only predict the MMM permeability under an implicit assumption that the interfacial equilibrium constant K and the diffusivity ratio of the filler and the matrix (Df/Dm) can be lumped into a single parameter, the permeability ratio Pf/Pm=KDf/Dm. It is shown here that the individual values of K and Df/Dm, and not the combined permeability ratio Pf/Pm, determine the MMM permeability. Our simulations also indicate that an ideal MMM shows no significant direct effect of filler particle size. We fit our computational data to an empirical correlation that can be easily and accurately used to calculate ideal MMM permeabilities, given equilibrium and diffusion data for the matrix and filler. We also examine some current issues regarding interpretation of MMM permeation behavior. For example, CO2 solubilities and diffusivities in representative MOF filler and polymer matrix materials are used to rigorously compare the ‘exact’ predictions with permeability-based models. The rigorous calculations show non-monotonic behavior of the MMM permeability as a function of the matrix permeability, which cannot be predicted by permeability-based models. Also, the ‘apparent’ CO2 permeability of ZIF-8 fillers extracted with Maxwell and Lewis–Nielsen models from the computational MMM permeation data, varies by 3 orders of magnitude depending upon the matrix polymer. Though the ZIF-8 filler maintains a constant permeability of ~3000 Barrer, the permeability models would require postulation of (spurious) non-idealities such as matrix-dependent filler behavior or interfacial rigidification to explain the results. Overall, this work provides a method for more reliable use of models to understand and design MMMs, as well as to better interpret the large and growing body of experimental data on these membranes.

Ultrasound-Assisted Pullulan/Montmorillonite Bionanocomposite Coating with High Oxygen Barrier Properties

In this paper, the preparation and characterization of oxygen barrier pullulan sodium montmorillonite (Na(+)-MMT) nanocomposite coatings are presented for the first time. Full exfoliation of platelets during preparation of the coating water dispersions was mediated by ultrasonic treatment, which turned out to be a pivotal factor in the oxygen barrier performance of the final material even at high relative humidity (RH) conditions [oxygen permeability coefficients ~1.43 ± 0.39 and 258.05 ± 13.78 mL·μm·m(-2)·(24 h)(-1)·atm(-1) at 23 °C and 0% RH and 70% RH, respectively]. At the micro- and nanoscale, the reasons are discussed. The final morphology of the coatings revealed that clay lamellae were stacked on top of one another, probably due to the forced confinement of the platelets within the coating thickness after solvent evaporation. This was also confirmed by modeling the experimental oxygen permeability data with the well-known Nielsen and Cussler permeation theoretical models, which suggested a reasonable aspect ratio (α) of ~100. Electron microscopic analyses also disclosed a peculiar cell-like arrangement of the platelets. The stacking of the clay lamellae and the cell-like arrangement create the excellent oxygen barrier properties. Finally, we demonstrated that the slight haze increase in the bionanocomposite coating materials arising from the addition of the clays depends on the clay concentration but not so much on the sonication time, due to the balance of opposite effects after sonication (an increase in the number of scattering centers but a reduction in their size).

Modelling of the thermal conductivity in polymer nanocomposites and the impact of the interface between filler and matrix

In this paper the thermal conductivity of epoxy-based composite materials is analysed. Two- and three-phase Lewis–Nielsen models are proposed for fitting the experimental values of the thermal conductivity of epoxy-based polymer composites. Various inorganic nano- and micro- particles were used, namely aluminium oxide, aluminium nitride, magnesium oxide and silicon dioxide with average particle size between 20 nm and 20 µm. It is shown that the filler–matrix interface plays a dominant role in the thermal conduction process of the nanocomposites. The two-phase model was proposed as an initial step for describing systems containing 2 constituents, i.e. an epoxy matrix and an inorganic filler. The three-phase model was introduced to specifically address the properties of the interfacial zone between the host polymer and the surface modified nanoparticles.

Analysis of tensile modulus of PP/nanoclay/CaCO3 ternary nanocomposite using composite theories

AbstractThe tensile modulus of PP/nanoclay/CaCO3 hybrid ternary nanocomposite was analyzed using composite models. Rule of mixtures, inverse rule of mixtures, modified rule of mixtures (MROM), Guth, Paul, Counto, Hirsch, Halpin–Tsai, Takayanagi, and Kerner–Nielsen models were developed for three‐phase system containing two nanofillers. Among the studied models, inverse rule of mixtures, Hirsch, Halpin–Tsai, and Kerner–Nielsen models calculated the tensile modulus of PP/nanoclay/CaCO3 ternary nanocomposite successfully compared with others. Furthermore, the Kerner–Nielsen model was simplified to predict the tensile modulus by volume fractions of nanofillers. Also, Takayanagi model was modified for the current ternary system. The developed Takayanagi model can predict the tensile modulus using Young's modulus and volume fractions of matrix and nanofillers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012