An-Najah Staff

The electronic structure, mechanical and thermodynamic properties of Fe2VX, (with
X = Al and Ga), have been studied self consistently by employing state-of-theart
full-potential linearized approach of augmented plane wave plus local orbitals
(FP-LAPW+lo) method. The exchange-correlation potential is treated with the local
density and generalized gradient approximations (LDA and GGA). Our predicted
ground state properties such as lattice constants, bulk modulus and elastic constants
appear more accurate when we employed the GGA rather than the LDA, and these
results are in very good agreement with the available experimental and theoretical data.
Further, thermodynamic properties of Fe2VAl and Fe2VGa are predicted with pressure
and temperature in the ranges of 0–40 GPa and 0–1500 K using the quasi-harmonic
Debye model. We have obtained successfully the variations of the heat capacities, primitive
cell volume and volume expansion coefficient.

We have shown in an earlier work that the addition of both organomodified layered silicates and micrometric calcium carbonate (CaCO3) into a polypropylene (PP) matrix resulted in improved mechanical properties due to synergistic effect of the fillers. In this study, we analyzed the feasibility of producing continuous glass fibers composites with micro/nanoreinforced matrix. In particular, either highly filled matrices with micrometric CaCO3 (22, 40, and 50 wt %) or micro/nanoreinforced matrix were used to prepare composites in order to investigate the effect of fillers on both mechanical and thermomechanical properties. The best mechanical performances were obtained when nano- and microsized particles were combined to reinforce the thermoplastic matrices employed in the film stacking manufacturing method. In such systems, the micro/nanocomposites have improved the flexural properties of the continuous fiber laminate, producing an increase of both flexural modulus (60%) and flexural strength (130%). Moreover, storage modulus of glass fibers composite prepared with micro/nanoreinforced matrix was higher than modulus of the composites manufactured with either neat PP matrix or microreinforced matrix in −40/150°C temperature range.

The stochastic nature and the variability of the constituents of nano-composites materials affect the predictability of their properties. The few studies that dealt with the probabilistic nature of the micromechanics of fibrous nano-composites, focused on the effect of statistical variation of individual parameters. This study presents a systematic analysis of the influence of parameter randomness on the theoretical predictions of the elastic properties of nano-composites. To this end, Monte-Carlo simulations are performed using a modified version of the Mori–Tanaka Mean-Field theory under different combinations of parameter randomness. The results indicate that the randomness in interface imperfection, fibre orientation and length, and fibre stiffness have a significant influence on the variability of the composite properties. The analysis provided an insight into the sensitivity of the predictions of the elastic tensor to the probabilistic variations of the aforementioned parameters. A probabilistic model for the effective properties is called for in place of deterministic models.

A simple and efficient methodology is developed for computing nonlinear stress–strain curve of unidirectional fibrous nano-composites loaded in the direction of the perfectly aligned fibers. The method, based on shear lag analysis and derived from basic principles of continuum micromechanics, incorporates shear stick–slip constitutive law at the fiber–matrix interface. The matrix is modeled as elastic–plastic with linear isotropic strain hardening. The approach thus predicts the nonlinear behavior of the composite stress–strain curve due to both interfacial shear slippage of reinforcement fibers within the matrix and due to spread of plasticity within the matrix. The proposed method is compared to experimental results on aligned fibrous nano-composites and very good agreement is obtained when low values of interfacial shear strength are used. The study shows that when the interfacial bond between the matrix and the fiber is strong, higher stress concentration leads to spread of plasticity in the composite at lower bulk strains. However, when the bond is weak, interfacial slippage causes a relief in the accumulation of stress in the matrix. Both factors seem to provide reasonable explanation for the observed nonlinearity and improved stiffness of the composite. A set of parametric studies is also performed and the proposed method is compared to existing models.

Poly(L-lactide) (PLLA) films exhibit toughening by the addition of oils to the polymer casting. This was investigated by casting films from solution and evaporation in air; the investigated oils were linear alkanes, cyclic alkanes, and two terpenes (limonene and eugenol). The addition of the oils greatly influenced the morphology and thermal and mechanical properties of the films. Most oils rendered porous films, and a variety of morphologies was obtained. Films prepared with hexane and eugenol showed a solid, nonporous structure similar to neat PLLA films, with similar mechanical properties. The thermal transition temperatures of the films decreased through the addition of oil, depending on the oil used, the decrease could be up to 30°C (glass transition), 45°C (cold crystallization), and 15°C (melting temperature). The films prepared without oil were stiff and brittle. Upon addition of most of the oils, the maximum strength and elastic moduli decreased, but their ductility improved considerably. Limonene, the most extreme case, gave a very ductile film with an elongation at break up to 200%. The main conclusion of this study is that various oils can be used to tune and improve the properties of PLLA films. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

In this study, the strength, ductility, and porosity of polylactide films prepared by immersion precipitation and film casting in air were investigated. To induce extra porosity in the films, dodecane was added to the polymer casting solution. The structure, porosity, and mechanical properties of the films were evaluated. The ultimate strength and elastic modulus of neat poly(L-lactide) prepared by film casting were at least twice those of the same film prepared in methanol, whereas the ductility of these films was considerably higher than that for air. The porosity, size of pores, and interconnectivity of pores increased gradually with increasing dodecane concentration. This dodecane-induced porosity (as high as 80%), progressively reduced the ultimate strength and modulus of practically all films but remarkably improved the ductility of films prepared in air, and this can be related to a decrease in the crystallization temperature. For films prepared in water or poly(D,L-lactide) films in general, the ultimate strength, modulus, and ductility of films prepared in water were significantly lower than those of air-cast poly(L-lactide) films. In summary, the results obtained in this research show that it is possible to tailor the properties of films for various biomedical applications through the use of the polymer type, preparation method, and dodecane-induced porosity as tools. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

There is a growing environmental concern in many countries around the world from the accumulation of solid waste glass since not all glass can be recycled into new glass. This study explores the recycling of solid waste glass in concrete mixtures to reduce the environmental pollution and to improve the properties of concrete material. Three waste glass powder (WGP) levels were considered in this study: 5%, 10% and 15%. The properties investigated include: setting time, workability, compressive and flexural strength and micro-structure of mortar. The mortar mixtures proportions were 1:3:0.7 by weight for cement, sand and water, respectively. The results showed that the solid waste glass can be recycled in cement concrete mixtures and improve the properties of concrete. The setting time of cement paste increased and the workability decreased with the increase of the WGP content. The compressive strength of mortar increased with the increase of WGP as partial replacement of limestone sand under moist curing. The flexural strength of mortar increased with the increase of WGP as partial replacement of cement or sand under moist curing. The autoclaved WGP mortar showed higher compressive strength and lower flexural strength compared to the moist cured mortar. The scanning electron microscopy images showed that WGP material is good filler because it reduced the porosity of mortar.