Deinked and acetylated fiber of newspapers

Recently, the incorporation of lignocellulosic materials as reinforcing agents or as fillers in polymer composites has received an increased attention. Although natural fibers have a number of advantages over glass fibers, the strong polar character of their surface is a limiting factor, as compatibility with strongly apolar thermoplastic matrices is very low. Such problems of incompatibility may be overcome with fiber pretreatments, which can enhance compatibility, albeit having a negative impact on the economics. In this study, the newspaper is deinked and acetylated. The effect of esterification between the acetyl groups and the hydroxyl groups of the fiber was examined by Fourier transform infrared. X‐ray diffraction and scanning electron microscopy were used to characterize the crystallinity and the surface morphology of the untreated deinked and acetylated fibers (newspaper). The thermal stability of deinked and acetylated fibers was slightly decreased. It was also shown that the deinking increased the crystallinity of newspaper fibers while acetylating decreased this crystallinity. Cellulose acetate is one of the most important cellulose derivatives and its main applications are its use in composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Simulation of ductile tearing by the BEM with 2D domain discretization and a local damage model

A numerical procedure based on the Boundary Element Method with internal cells and dedicated to the simulation of the ductile tearing of thin metal sheets is presented. Plasticity is handled with an integral formulation based on the initial strain approach involving a discretization of the planar domain. Time integration is performed in an implicit way for the local strain-stress relationships while the global algorithm relies on an explicit formulation. Damage is represented by the scalar parameter of the uncoupled local damage model of Rice and Tracey. Within the scope of our applications, the cracks propagate along paths a priori known. As damage spreads, boundary elements are gradually released. Elastoplastic problems with large yielding zones are solved and compared to reference solutions. At last, the ductile tearing of a specimen is addressed. The calibration of the critical damage parameter leads to numerical results in good agreement with the experimental ones.     

Prediction of reliability analysis of composite tubular structure under hygro-thermo-mechanical loading

The present paper focuses on reliability prediction of composite structure under hygro-thermo-mechanical loading, conditioned by Tsai-Wu failure criterion, where the Monte–Carlo method is used to estimate the failure probability(Pf). This model was developed in two steps: first, the development of a deterministic model, based on an analytical and numerical approach, and then, a probabilistic computation. Using the hoop stress for each ply, a sensitivity analysis was performed for random design variables, such as materials properties, geometry, manufacturing, and loading, on composite cylindrical structure reliability. The probabilistic results show the very high increase of failure probability when all parameters are considered.     

Personal monitor glass badge: theoretical dosemeter response calculated with the Monte Carlo transport code MCNPX

This paper describes the results of the simulation of a radiophotoluminescent (RPL) dosemeter with the Monte Carlo transport code MCNPX. The aim of this study is to calculate the response with MCNPX of the RPL dosemeter in terms of equivalent doses H(p) (0.07) and H(p)(10) using X-ray photon radiation qualities N series, together with S-Cs and S-Co nuclide radiation qualities, specified in ISO 4037-1. After comparison with reference values versus experimental results, the deviation of the theoretical responses of the RPL dosemeter proved to be lower than 5 % for reference values and lower than 10 % for experimental results. This good correlation validates the model over the energy range studied.     

Fracture problems of rubbers: J-integral estimation based upon η factors and an investigation on the strain energy density distribution as a local criterion

The plane elasticity problem studied is of a circular inclusion having a circular arc-crack along the interface and a crack of arbitrary shape in an infinite matrix of different material subjected to uniform stresses at infinity. The solution of the problem is given using Muskhelishvili's complex variable method with sectionally holomorphic functions. First, the solution to the (auxiliary) problem of a dislocation (or force) applied at a point in the matrix with the circular inclusion partially bonded is derived fully in its general form by solving the appropriate Rieman-Hilbert problem. It is subsequently used as the Green's function for the initial problem by introducing an unknown density function associated with a distribution of dislocations along the crack in the matrix. The initial problem is then reduced to a singular integral equation (SIE) over the crack in the matrix only. The SIE is solved numerically by appropriate quadratures and the stress intensity factors reported for the arc-cut and a straight crack in the matrix for a range of values of the geometrical parameters.     

Maximum likelihood difference scaling of image quality in compression-degraded images

Lossy image compression techniques allow arbitrarily high compression rates but at the price of poor image quality. We applied maximum likelihood difference scaling to evaluate image quality of nine images, each compressed via vector quantization to ten different levels, within two different color spaces, RGB and CIE 1976 L*a*b*. In L*a*b* space, images could be compressed on average by 32% more than in RGB space, with little additional loss in quality. Further compression led to marked perceptual changes. Our approach permits a rapid, direct measurement of the consequences of image compression for human observers.     

Properties of poly(lactic acid)/montmorillonite/carbon nanotubes nanocomposites: determination of percolation threshold

Incorporation of rigid nanoparticles is the most effective means of improving polymer properties. Montmorillonite (MMT) and multi-walled carbon nanotubes (MWCNTs) are legendary in this field for their individual exceptional properties. A synergistic phenomenon is induced between these two particles when they are simultaneously incorporated into polymers. At a definite nanofillers concentration, called the percolation threshold, there is a sudden change in nanocomposite properties due to the formation of a 3D-structured network of the nanoparticles within the matrix. In this work, the properties of poly(lactic acid) (PLA) nanocomposites filled with different fractions of MMT/MWCNTs hybrid (0.5–2.0 wt%) were analyzed. In particular, the percolation threshold of the MMT/MWCNTs hybrid was uniquely identified by differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical thermal analysis. The structural studies by X-ray diffraction and Fourier-transform infrared spectroscopy were also associated with the percolation threshold of MMT/MWCNTs in PLA. At 1.0 wt% MMT/MWCNTs concentration, the complete exfoliation of the particles was maintained, and the thermal characteristics such as glass transition, crystallization and melting temperatures reached their plateau at this hybrid concentration. Moreover, the thermal degradation and viscoelastic parameters showed their peak values at this critical point, which is correlated with the formation of the percolation threshold within the matrix. The morphological studies confirmed the homogeneous dispersion of MMT/MWCNTs in PLA up to a concentration of 1.0 wt%. At 2.0 wt% MMT/MWCNTs, few aggregations occurred in the PLA-based composite, confirming that the percolation threshold was formed at a lower concentration of MMT/MWCNTs nanoparticles.

     

Dual boundary element method modelling of aircraft structural joints with multiple site damage

The computation of crack growth from a bolt or rivet hole in a structural joint practically requires that the geometry be approximated to some degree. In this paper a simplified quasi-2D stress analysis method, using the boundary element method is presented, where the load transfer rate and the contact stresses at the hole edge for the full 3D geometry are fairly well approximated. Coupled with a dual boundary element formulation for the crack propagation problem, this model is used to evaluate stress intensity factors for through cracks emanating from holes in several double shear lap joint configurations. As the calculated stress intensity factors compare well with experimental data, this procedure is considered to approximate satisfactorily the load transfer rate and the contact stresses at the hole edge of the full 3D geometry, when secondary bending is not a factor.     

FGF‐23 and cognitive performance in hemodialysis patients

Although cognitive impairment is common in hemodialysis patients, the etiology of and risk factors for its development remain unclear. Fibroblast growth factor 23 (FGF‐23) levels are elevated in hemodialysis patients and are associated with increased mortality and left ventricular hypertrophy. Despite FGF‐23 being found within the brain, there are no prior studies assessing whether FGF‐23 levels are associated with cognitive performance. We measured FGF‐23 in 263 prevalent hemodialysis patients in whom comprehensive neurocognitive testing was also performed. The cross‐sectional association between patient characteristics and FGF‐23 levels was assessed. Principal factor analysis was used to derive two factors from cognitive test scores, representing memory and executive function, which carried a mean of 0 and a standard deviation of 1. Multivariable linear regression adjusting for age, sex, education status, and other relevant covariates was used to explore the relationship between FGF‐23 and each factor. Mean age was 63 years, 46% were women and 22% were African American. The median FGF‐23 level was 3098 RU/mL. Younger age, lower prevalence of diabetes, longer dialysis vintage, and higher calcium and phosphorus were independently associated with higher FGF‐23 levels. Higher FGF‐23 was independently associated with a lower memory score (per doubling of FGF‐23, β = ?0.08 SD [95% confidence interval, CI: ?0.16, ?0.01]) and highest quartile vs. lowest quartile (β = ?0.42 SD [?0.82, ?0.02]). There was no definite association of FGF 23 with executive function when examined as a continuous variable (β = ?0.03 SD [?0.10, 0.04]); however, there was a trend in the quartile analysis (β = ?0.28 SD [?0.63, 0.07], P = 0.13, for 4th quartile vs. 1st quartile). FGF‐23 was associated with worse performance on a composite memory score, including after adjustment for measures of mineral metabolism. High FGF‐23 levels in hemodialysis patients may contribute to cognitive impairment.