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Heidari-Rarani M.,University of Isfahan | Aliha M.R.M.,Iran University of Science and Technology | Shokrieh M.M.,Composites Research Laboratory
Construction and Building Materials | Year: 2014

Investigating the tensile strength (σt) and mode I fracture toughness (KIc) of polymer concrete (PC) materials due to their quasi-brittle behavior is of great interest to engineers. In this paper, the mechanical durability of an optimized epoxy PC, focused on the two above properties, are experimentally investigated under three different freeze/thaw cycles. The diametrally compressed un-cracked Brazilian disc (BD) and the single edge notch bending (SENB) test configurations are used to measure the split tensile strength and fracture toughness, respectively. The thermal cycles; 25 °C to -30°C (cycle-A), 25°C to 70°C (cycle-B) and -30°C to 70°C (cycle-C) applied for 7 days to the test specimens; are chosen according to the climate of Iran in different seasons. Experimental results show the noticeable influence of thermal cycles, especially cycle-B, on both fracture toughness and tensile strength. Heat-to-cool thermal cycle-A and thawing thermal cycle-B indicate the most increase and reduction, respectively on both σt and KIc in comparison to ambient conditions. Also, it was shown that the fracture toughness and tensile strength of tested PC materials are reduced by increasing the mean temperature values of thermal cycles. © 2014 Elsevier Ltd. All rights reserved.

Shokrieh M.M.,Composites Research Laboratory | Moshrefzadeh-Sani H.,Iran University of Science and Technology
Journal of Composite Materials | Year: 2016

The micromechanical prediction of mechanical properties of composites, using a finite element method, is highly affected by selecting a suitable representative volume element. In the present research, the effects of the representative volume element aspect ratio on the stiffness of aligned short fiber composites have been studied. First, an analytical method is suggested to predict the longitudinal and transverse moduli of composites considering the representative volume element aspect ratio. Then, the optimum aspect ratio of the representative volume element is estimated by comparing the results obtained by the present method with those of a micromechanical method. Comparing the stiffness of the optimized representative volume element with some experimental results available in the literature shows that the result of the present method is also in a good agreement with experiments. © SAGE Publications.

Chitsazzadeh M.,Nanotechnology Group | Shahverdi H.,Nanotechnology Group | Shokrieh M.M.,Composites Research Laboratory
Defect and Diffusion Forum | Year: 2011

Excellent physical and mechanical properties of carbon nanotubes (CNTs) make them outstanding candidate as fillers to fabricate multi-functional polymer composites. It is assumed that a high level of dispersion in the preparation stage may lead to a more effective nanocomposite. In this research, the dispersion state of multi-walled carbon nanotubes (MWNTs) at various contents in an unsaturated vinyl ester resin is investigated during fabrication by on-line monitoring the viscosity of suspensions as a function of sonication time and energy introduced. The results show that initial viscosities of suspensions increase by adding more MWNTs to the resin. The viscosities gradually increase during the sonication and reach to maximum values, when it is assumed that the dispersion is completed. After this step the viscosity subsequently decreases. The energy density required to achieve a good dispersion of MWNTs in vinyl ester is obtained. The qualities of dispersion in cured composites are characterized by examining the sections using the scanning electron microscope (SEM) to confirm the results of viscosity measurements. The stabilization of MWNTs is achieved by adding a commercial dispersant and stabilizer, BYK-P 104S, by 0.0375 wt%. The results indicate that adding more surfactant to the suspension makes it unstable and leads to flocculation. The stabilization of suspensions is investigated by using viscosity measurement. Also, FT-IR is used to determine the possible mechanism of surfactant to stabilize the MWNTs in vinyl ester. © (2011) Trans Tech Publications.

Elhamian S.M.M.,Iran University of Science and Technology | Elhamian S.M.M.,Composites Research Laboratory | Alizadeh M.,Iran University of Science and Technology | Shokrieh M.M.,Composites Research Laboratory | And 3 more authors.
Materials Technology | Year: 2014

Owing to a variation of collagen fibres orientation through the zones of articular cartilage, it shows a depth dependent transversely isotropic mechanical behaviour. This study characterised the role of collagen fibre angle toward cartilage surface φ on the mechanical properties of articular cartilage with an innovative micromechanics (multi-direction composite MDC) model. The role of collagen fibres, their volume fraction as well as angle φ in all zones of articular cartilage, was embedded into the MDC model. Variation of collagen fibre angle toward the cartilage surface as a function of cartilage depth was calculated. According to this function, collagen fibres are parallel to cartilage surface in superficial zone, have a nonlinear angle variation in transition zone and become perpendicular to the cartilage surface in the deep zone. The results revealed that owing to constancy of the mechanical properties of articular cartilage components and slight variation of fibres volume fraction through the depth of cartilage, variations of collagen fibre angle φ has the most important role in depth dependent variation of the mechanical properties of the articular cartilage. As elastic modulus parallel to cartilage surface is decreased by increasing the fibre angle qua radial elastic modulus in superficial zone is 10·2 times greater than deep zone, but elastic modulus perpendicular to cartilage surface is increased by increasing the fibre angle qua axial elastic modulus in superficial zone is 28·3 times smaller than deep zone. © 2014 W. S. Maney & Son Ltd.

Shokrieh M.M.,Composites Research Laboratory | Karamnejad A.,Mechani. engin.depart. of Iran Univer. of Science and Technology
World Academy of Science, Engineering and Technology | Year: 2011

This paper deals with a numerical analysis of the transient response of composite beams with strain rate dependent mechanical properties by use of a finite difference method. The equations of motion based on Timoshenko beam theory are derived. The geometric nonlinearity effects are taken into account with von Kármán large deflection theory. The finite difference method in conjunction with Newmark average acceleration method is applied to solve the differential equations. A modified progressive damage model which accounts for strain rate effects is developed based on the material property degradation rules and modified Hashin-type failure criteria and added to the finite difference model. The components of the model are implemented into a computer code in Mathematica 6. Glass/epoxy laminated composite beams with constant and strain rate dependent mechanical properties under dynamic load are analyzed. Effects of strain rate on dynamic response of the beam for various stacking sequences, load and boundary conditions are investigated.

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