Search results for "Number"
showing 10 items of 3939 documents
Hygrothermal effect on moisture kinetics and mechanical properties of hemp/polypropylene composite: Experimental and numerical studies
2015
The exposition of thermoplastic composites reinforced with natural fibers to moisture and heat is likely to lower their mechanical properties and restrain their use in the design of parts. The present work is focussed on investigating the effects of hygrothermal aging on the mechanical behaviour of injected polypropylene reinforced with short hemp fibers. Moreover, the kinetic of isothermal moisture absorption has been studied for four immersion temperatures. The experimental results show that the time taken to reach saturation decreases significantly with increase in immersion temperature. These tests also reveal that moisture absorption in this type of materials does not follow Fick's law…
Model of the mechanical response of short flax fiber reinforced polymer matrix composites
2011
Abstract Natural-fiber-reinforced short-fiber composites are finding more applications lately, therefore there is a need for estimation of the mechanical properties of such composites based on the properties of the constituents. The fibers themselves also possess complicated internal structure, resulting in anisotropy of their properties. Taking into account the internal structure of bast fiber, we evaluate the elastic properties of a composite unit cell, consisting of a fiber of average length and matrix according to the fiber volume fraction in the composite. The unit cell properties are used to estimate the stiffness of a misaligned short-fiber composite by means of orientation averaging…
Influence of low amounts of nanostructured silica and calcium carbonate fillers on the large-area dielectric breakdown performance of bi-axially orie…
2014
Influence of low amounts (1.0-2.0wt-%) of nanostructured silica and calcium carbonate fillers on the large area dielectric breakdown performance of bi-axially oriented polypropylene (BOPP) is analyzed. A multi-breakdown measurement method based on the self-healing breakdown capability of metallized film is utilized for the breakdown characterization in order to cover relatively large total film areas, thus leading to results of higher relevance from the practical point-of-view. The dispersion and distribution qualities of filler particles at the nanoscale are evaluated with transmission electron microscopy (TEM) imaging. Weibull statistical analysis suggests that the breakdown distribution …
Modeling elastic properties of short flax fiber-reinforced composites by orientation averaging
2010
Abstract Natural fibers of plant origin, used as reinforcement in polymer matrix composite materials, exhibit highly anisotropic elastic properties due to their complex internal structure. Mechanical properties can be evaluated not only by tests but also by mechanical models reflecting the principal morphological features of fibers. Such a FEM model is applied to estimate the elastic properties of a unit cell of a short-fiber-reinforced composite, an elementary flax fiber embedded in a polymer matrix. Orientation averaging approach is used for prediction of the stiffness of short flax fiber reinforced polymer matrix composite. The numerical estimates of Young’s modulus are compared to the t…
Properties of PP/MWCNT-COOH /PP composites made by melt mixing versus solution cast /melt mixing methods
2015
An approach on improvement of the properties of polypropylene / carbon nanotube (PP/CNT) composites is reported. PP blend compositions with carboxylic acid functionalized multi-walled carbon nanotubes (MWCNT-COOH) at filler content 1.0 wt.% were researched. One part of the composites was manufactured by direct thermoplastic mixing PP with the filler, but the other one was made from solution casted masterbatch with the following thermoplastic mixing. An increase of mechanical properties (Young's modulus, storage modulus and tensile strength), compared to an increase of glass transition temperature indicated a reinforcement effect of CNTs on PP matrix, determined from the tensile tests and di…
Genetic diversity within the R408W phenylketonuria mutation lineages in Europe
2003
The R408W phenylketonuria mutation in Europe has arisen by recurrent mutation in the human phenylalanine hydroxylase (PAH) locus and is associated with two major PAH haplotypes. R408W-2.3 exhibits a west-to-east cline of relative frequency reaching its maximum in the Balto–Slavic region, while R408W-1.8 exhibits an east-to-west cline peaking in Connacht, the most westerly province of Ireland. Spatial autocorrelation analysis has demonstrated that the R408W-2.3 cline, like that of R408W-1.8, is consistent with a pattern likely to have been established by human dispersal. Genetic diversity within wild-type and R408W chromosomes in Europe was assessed through variable number tandem repeat (VNT…
Stability and l1-gain analysis for positive 2D T–S fuzzy state-delayed systems in the second FM model
2014
This paper considers the problems of delay-dependent stability and l"1-gain analysis for a class of positive two-dimensional (2D) Takagi-Sugeno (T-S) fuzzy linear systems with state delays described by the second FM model. Firstly, the co-positive type Lyapunov function method is applied to establish sufficient conditions of asymptotical stability for the addressed positive 2D T-S fuzzy system. Then, the l"1-gain performance analysis for the positive 2D T-S fuzzy delayed system is studied. All the obtained results are formulated in the form of linear matrix inequalities (LMIs) which are computationally tractable. Finally, an illustrative example is given to verify the effectiveness of the p…
Exploring the concept of causal power in a critical realist tradition
2007
This article analyses and evaluates the uses of the concept of causal power in the critical realist tradition, which is based on Roy Bhaskar's philosophy of science. The concept of causal power that appears in the early works of Rom Harre and his associates is compared to Bhaskar's account of this concept and its uses in the critical realist social ontology. It is argued that the concept of emergence should be incorporated to any adequate notion of causal power. The concept of emergence used in Bhaskar and other critical realists' works is shown to be ambiguous. It is also pointed out that the concept of causal power should be analysed in an anti-essentialist way. Ontological and methodolog…
Thermally unstable throughflow of a power–law fluid in a vertical porous cylinder with arbitrary cross–section
2021
Abstract The present paper investigates how the cross–sectional shape of a vertical porous cylinder affects the onset of thermoconvective instability of the Rayleigh–Benard type. The fluid saturating the porous medium is assumed to be a non–Newtonian power–law fluid. A linear stability analysis of the vertical thorughflow is carried out. Three special shapes of the cylinder cross–section are analysed: square, circular and elliptical. The effect of changing the power–law index is investigated. The stability of a steady base state with vertical throughflow is analysed. The resulting stability problem is a differential eigenvalue problem that is solved numerically through the shooting method. …
Linear instability of the vertical throughflow in a horizontal porous layer saturated by a power-law fluid
2016
Abstract The effects of the vertical throughflow of a non-Newtonian power-law fluid on the onset of convective instability in a horizontal porous layer are investigated. The extended Darcy’s model of momentum diffusion is employed together with the Oberbeck–Boussinesq approximation. A stationary basic solution for the vertical throughflow is determined analytically. The basic velocity and temperature fields turn out to be independent of the non-Newtonian rheology. A linear stability analysis is carried out, leading to a fourth-order eigenvalue problem. A numerical solution of the eigenvalue problem is employed to obtain the neutral stability curves and the critical Rayleigh number for the o…