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Papers by Samrand Rash-Ahmadi

Chugoku Shikoku Shibu Sokai, koenkai koen ronbunshu, Feb 26, 2008

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

Surface interactions between epoxy matrices and graphene nanosheets can directly affect the prope... more Surface interactions between epoxy matrices and graphene nanosheets can directly affect the properties of nanocomposites, and such interactions are crucial to investigate. In this study, molecular dynamics simulation was used to investigate the interaction rate between epoxy thermoset resins (EPON 828, EPON 862, Epoxy Novolac, and Cycloaliphatic Epoxy) with graphene, and Functionalized Graphene with Oxygen Functional Groups. The effect of temperatures and different weight percentage of graphene oxide (1, 3, and 5 wt.%) was studied, and as a result of which it was observed that increasing the weight percentage of graphene oxide improved the interaction energy (adhesion) between epoxy resins and graphene oxide. Also, it decreased the radius of gyration (more contraction of epoxy molecules than graphene oxide nanosheets). In addition, increasing the temperature led to reduction of the interaction energy between epoxy resins and functionalized graphene. Moreover, escalating the temperat...

Journal of Molecular Graphics and Modelling

Design of a constant chord propeller is presented in this paper in order to reduce propeller-s de... more Design of a constant chord propeller is presented in this paper in order to reduce propeller-s design procedure-s costs. The design process was based on Lock and Goldstein-s techniques of propeller design and analysis. In order to calculate optimum chord of propeller, chord of a referential element is generalized as whole blades chord. The design outcome which named CS-X-1 is modeled & analyzed by CFD methods using K-ε: R.N.G turbulence model. Convergence of results of two codes proved that outcome results of design process are reliable. Design result is a two-blade propeller with a total diameter of 1.1 meter, radial velocity of 3000 R.P.M, efficiency above .75 and power coefficient near 1.05.

International journal of engineering. Transactions A: basics, 2017

The Newmark method is an effective method for numerical time integration in dynamic problems. The... more The Newmark method is an effective method for numerical time integration in dynamic problems. The results of Newmark method are function of its parameters (β, γ and ∆t). In this paper, a stationary mode I dynamic crack problem is coded in extended finite element method )XFEM( framework in Matlab software and results are verified with analytical solution. This paper focuses on effects of main parameters in Newmark method for dynamic XFEM problems. Also use of the response surface method (RSM) a regression model is presented for estimating error of dynamic stress intensity factors (DSIF) with high validity according to results of analysis of variance (ANOVA). This work enables one to understand the effect of Newmark parameters on error of DSIFs and to find optimum β and γ for a determined number of time steps (N). This procedure is highly effective in order to manage the computational cost and enhance the accuracy at the desired domain. The effect of the considered parameters on erro...

International Applied Mechanics, 2017

Journal of Mechanics, 2017

Poly methyl methacrylate (PMMA) was melt compounded with different nanoparticles using a twin-scr... more Poly methyl methacrylate (PMMA) was melt compounded with different nanoparticles using a twin-screw extruder. Nano TiO2, SiO2 and Al2O3 in 0.5, 1 and 2 wt% were added to the polymeric matrix as reinforcements. Nine polymeric nanocomposite samples were injection molded. Impact strength, Young's modulus, Rockwell hardness-R and cost of raw materials were considered as different criteria. Two procedures of multi-criteria decision making (MCDM) methods were performed for solving material selection problem. Criteria weighting was performed using analytical hierarchy process (AHP). According to weights that obtained from AHP, the alternative ranking was implemented using TOPSIS (the technique for order preference by similarity to ideal solution) and MOORA (multi-objective optimization on the basis of ratio analysis) methods. The results indicated that the addition of nanoparticles to the polymeric matrix was significantly improved mechanical properties. The results showed a 94% and 22...

International Journal of Engineering, 2017

Various applications of nanocomposites were a good motivation to start a study on this wide sprea... more Various applications of nanocomposites were a good motivation to start a study on this wide spreading field of science. Current research is an investigation on incorporating different percentages of TiO2 nanoparticle as reinforcement to a base material which here is poly methyl methacrylate (PMMA). In this study various percentages of TiO2 (0.5, 1 and 2 wt%) were added to pure PMMA and effect of this combination on the mechanical properties of produced composite by performing several tests was investigated and compared to the base material. For producing samples, materials were compounded by melting compounding method using a twin screw extruder followed by injecting molding process. SEM images showed that almost all percentage of TiO2 nanoparticles have been mixed suitably through base matrix. Rockwell hardness R, impact and tensile tests were carried out on all specimens. Almost all of the results illustrated that combination of TiO2 nanoparticle with PMMA, improves mechanical pro...

This paper investigates the pull-in instability of graphene sheets. The influence of geometry par... more This paper investigates the pull-in instability of graphene sheets. The influence of geometry parameters such as chirality of graphene and length to gap ratio is studied using molecular dynamics (MD). For molecular interactions, the AIREBO potential is used. Furthermore, by applying the electrostatic and van der Waals (vdW) forces, pull-in voltages are calculated. Size effect is estimated, with adding the fringing field effect correction factor to the electrostatic force. In MD simulations, the graphene sheets on the armchair and zigzag structure have been investigated. The results show that the closer the moving electrode to the fixed electrode, the greater the effect of van der Waals force than the electrostatic force. The results also represent that the vdW force and fringing effect on the electrostatic load increases the pull-in deflection and decrease the pull-in voltage. The numerical results of the present study show good agreement with previous analytical and experimental re...

Applied Mathematical Modelling, 2019

Polymer-Plastics Technology and Engineering, 2017

Sensors and Actuators A: Physical, 2019

Journal of Composite Materials, 2021

This paper aimed to evaluate hygrothermal aging effects on polymethyl methacrylate modified with ... more This paper aimed to evaluate hygrothermal aging effects on polymethyl methacrylate modified with TiO2, SiO2, and Al2O3 nanoparticles in 0.5, 1, and 2% weight fractions. The distribution of nanoparticles was characterized by the scanning electron microscopy (SEM) method. Moisture absorption behavior and mechanical properties of samples in terms of elastic modulus, tensile strength, impact strength, and hardness were investigated. Furthermore, the coefficient of hygrothermal expansion (CHE) for each sample was calculated thanks to experimental data. Finally, by applying the multi-criteria decision making (MCDM) technique, the optimum composition for superior performance was obtained in 0.5 wt% of nanoparticles, more specifically for SiO2.

Mechanics Based Design of Structures and Machines, 2020

$Research paper thumbnail of Effect of the interphase properties on the fracture energy and fatigue behavior of thermoset resins containing spherical fillers$

Journal of Applied Polymer Science, 2021