Mahdi Karami Khorramabadi - Academia.edu (original) (raw)

Papers by Mahdi Karami Khorramabadi

Journal of Solid Mechanics, Apr 30, 2009

This paper studies free vibration of simply supported functionally graded beams with piezoelectri... more This paper studies free vibration of simply supported functionally graded beams with piezoelectric layers subjected to axial compressive loads. The Young's modulus of beam is assumed to be graded continuously across the beam thickness. Applying the Hamilton's principle, the governing equation is established. Resulting equation is solved using the Euler's Equation. The effects of the constituent volume fractions, the influences of applied voltage and axial compressive loads on the vibration frequency are presented. To investigate the accuracy of the present analysis, a compression study is carried out with a known data.

ADMT Journal, Mar 1, 2020

In this paper, the theoretical predictions of mechanical properties of functionally graded and un... more In this paper, the theoretical predictions of mechanical properties of functionally graded and uniform distributions Epoxy/clay nanocomposites are presented. The specimens were prepared for uniformly distribution of nanoclay with different nano particles weight percent (pure, 3 wt%, 5 wt% and 7 wt%) and functionally graded distribution. The distribution of nanoparticles has been investigated by Field Emission Scanning Electron Microscopy (FESEM). For uniformly distribution of nanoclay, it is shown that there is no sign of the agglomerates found via FESEM imaging which can address well the distribution of nanoclay particles in epoxy. In addition, for functionally graded distributions, it is found that dispersion of nanoclays vary smoothly and continuously from one surface to the other one. The mechanical properties have been determined by simple extension tests. The results of extension tests show that elastic modulus begins to increase up to 5 wt% of nanoclay and then decreases. So, for functionally graded distribution, the elastic modulus is generally larger than the corresponding values for uniform distribution of nanoclay. The theoretical predictions of Young's modulus for functionally graded and uniform distributions nanocomposites are calculated using a genetic algorithm procedure. The formulation for Young modulus includes the effect of nanoparticles weight fractions and it is modified for functionally graded distribution. To investigate the accuracy of the present theoretical predictions, a comparison is carried out with the experimental results. It is found that the results obtained from the theoretical predictions of genetic algorithm procedure are in good agreement with the experimental ones.

This paper deals with an analytical approach of the buckling behavior of a functionally graded ci... more This paper deals with an analytical approach of the buckling behavior of a functionally graded circular cylindrical shell under axial pressure with external axial and circumferential stiffeners. The shell properties are assumed to vary continuously through the thickness direction. Fundamental relations and equilibrium and stability equations are derived using the third-order shear deformation theory. The resulting equations are employed to obtain the closed-form solution for the critical buckling loads. A simply supported boundary condition is considered for both edges of the shell. The comparison of the results of this study with those in the literature validates the present analysis. The effects of material composition (volume fraction exponent), of the number of stiffeners and of shell geometry parameters on the characteristics of the critical buckling load are described. The analytical results are compared and validated using the finite-element method. The results show that the inhomogeneity parameter, the geometry of the shell and the number of stiffeners considerably affect the critical buckling loads.

Journal of Solid Mechanics, Jun 30, 2009

In this paper, the causes of the crack initiation in cast iron bullion moulds in Meybod Steel Cor... more In this paper, the causes of the crack initiation in cast iron bullion moulds in Meybod Steel Corporation are investigated and then some new geometrical models are presented to replace the current moulds. Finally, among the new presented models and according to the life assessment, the best model is selected and suggested as the replaced one. For this purpose, the three recommended moulds were modeled and analyzed by ANSYS software. First, a thermal analysis and then a thermo-mechanical coupled field analysis were performed on each three model. The results of the analysis are used to determine the critical zone. The critical zone is selected on the symmetric axis of the inner surface of the mould. By comparing the principle stress contours and temperature distribution contours of three models, one of the suggested models was selected as optimized geometrical model. Then, the crack modeling and the life assessment on the optimized model were implemented and the total life of the model was calculated. Comparison of the life of the optimized and the initial models shows an increase in the life of the suggested model. The results are verified with the experiments.

World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering, Aug 20, 2009

The static stability analysis of stiffened functionally graded cylindrical shells by isotropic ri... more The static stability analysis of stiffened functionally graded cylindrical shells by isotropic rings and stringers subjected to axial compression is presented in this paper. The Young's modulus of the shell is taken to be function of the thickness coordinate. The fundamental relations, the equilibrium and stability equations are derived using the Sander's assumption. Resulting equations are employed to obtain the closed-form solution for the critical axial loads. The effects of material properties, geometric size and different material coefficient on the critical axial loads are examined. The analytical results are compared and validated using the finite element model.

Journal of Solid Mechanics, Mar 1, 2018

This paper presents the preparation and mechanical properties of compatibilized compositionally g... more This paper presents the preparation and mechanical properties of compatibilized compositionally graded Polyethylene/ low density polyethylene (LDPE)/ modified montmorillonite (MMT) nanocomposites prepared by solution and melt mixing techniques. Use of polyethylene glycol as compatibilizer improves compatibility of modified montmorillonite and low density polyethylene. Comparisons between two techniques show that the melt mixing technique is the preferred method for preparation the Polyethylene/Clay nanocomposites for uniform and compositionally graded distributions. It is observed, the addition of Nano clay improves the mechanical properties like tensile strength. Also, it is noticed the mechanical properties of compositionally graded Polyethylene/Clay nanocomposites are improved rather than the uniform distribution of Polyethylene/Clay nanocomposites. The morphology of nanocomposites cross section samples is studied by Scanning Electron Microscopy (SEM) and finally the comparison are made between two techniques and then between compositionally graded polyethylene/clay nanocomposites with uniform ones. Its show that when the compatibilizer was added for melt mixing technique, the density and the size of the aggregates decreased, which indicates that the dispersion of nano clays within the polymer matrix is much better.

Journal of Theoretical and Applied Mechanics, Jul 20, 2018

This paper deals with mechanical buckling of polyethylene/clay nanocomposite beams of functionall... more This paper deals with mechanical buckling of polyethylene/clay nanocomposite beams of functionally graded and uniformly distributed of nanoclay subjected to axial compressive load with simply supported conditions at both ends. The Young moduli of functionally graded and uniformly distributed nanocomposites are calculated using a genetic algorithm procedure and then compared with experimental results. The formulation is modified to include the effect of nanoparticles weight fractions in the calculation of the Young modulus for uniform distribution. Also, it is modified to take into account the Young modulus as a function of the thickness coordinate. The displacement field of the beam is assumed based on the Engesser-Timoshenko beam theory. Applying the Hamilton principle, governing equations are derived. The influence of nanoparticles on the buckling load of the beam is presented. To investigate the accuracy of the present analysis, a compression study with the experimental results is carried out.

Zenodo (CERN European Organization for Nuclear Research), Dec 26, 2008

Analytical solution of the first-order and third-order shear deformation theories are developed t... more Analytical solution of the first-order and third-order shear deformation theories are developed to study the free vibration behavior of simply supported functionally graded plates. The material properties of plate are assumed to be graded in the thickness direction as a power law distribution of volume fraction of the constituents. The governing equations of functionally graded plates are established by applying the Hamilton's principle and are solved by using the Navier solution method. The influence of side-tothickness ratio and constituent of volume fraction on the natural frequencies are studied. The results are validated with the known data in the literature.

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Journal of Health Administration, 2018

Increasing the productivity of health care spending is important for all countries. In order to i... more Increasing the productivity of health care spending is important for all countries. In order to increase productivity, input and output data can have fuzzy values. This study aimed to present a new model of inadequate envelopment analysis to determine the productivity of provinces in the health sectors, highlight productive provinces and detect sensitive indexes to increase productivity. Methods: This descriptive-analytical study was conducted on the health system of Iran in 2016. Data were collected through library documents, Internet and the center of statistics and information technology management of medical universities. Analytical hierarchy process was used to determine health care indexes among which five indicators were extracted. Data were analyzed using inadequate envelopment analysis technique by General Algebraic Modeling System. Results: According to the proposed model, for and, only Semnan, Kurdistan and Mazandaran provinces were considered to be efficient based on their indexes on patient satisfaction and physician-to-population ratio, and were regarded as referral units for other provinces. The two indexes of physician-to-population ratio and nurse-to-population ratio were introduced as the most and the least sensitive indicators, respectively. Conclusions: Kurdistan, based on the most sensitive indicator, had the highest referral patients. Other provinces can increase their efficiency through improving the quality and quantity of their services, increasing patient satisfaction, continuous evaluation of performance and increasing the number of physicians working in medical universities.

This paper deals with free vibration of epoxy/clay nanocomposite beams for functionally graded an... more This paper deals with free vibration of epoxy/clay nanocomposite beams for functionally graded and uniformly distributed of Nanoclay with simply supported conditions at both ends. The specimens were prepared for uniformly distributed of Nanoclay with different Nanoparticles weight percent (pure, 3 wt%, 5 wt% and 7 wt%) and functionally graded distribution. To apply the model of theoretical predictions for the Young modulus, the genetic algorithm procedure was employed for functionally graded and uniformly distributed epoxy/clay nanocomposites and then were compared with the experimental tensile results. The formulation for Young modulus includes the effect of nanoparticles weight fractions and it is modified for functionally graded distribution to take into account the Young modulus as a function of the thickness coordinate. The displacement field of the beam is assumed based on the first order shear deformation beam theory. Applying the Hamilton principle, the governing equations a...

Journal of Solid Mechanics, 2009

This paper studies free vibration of simply supported functionally graded beams with piezoelectri... more This paper studies free vibration of simply supported functionally graded beams with piezoelectric layers subjected to axial compressive loads. The Young's modulus of beam is assumed to be graded continuously across the beam thickness. Applying the Hamilton’s principle, the governing equation is established. Resulting equation is solved using the Euler’s Equation. The effects of the constituent volume fractions, the influences of applied voltage and axial compressive loads on the vibration frequency are presented. To investigate the accuracy of the present analysis, a compression study is carried out with a known data. © 2009 IAU, Arak Branch. All rights reserved.

Journal of Theoretical and Applied Mechanics, 2018

In this paper, uncoupled thermopiezoelastic analysis of functionally graded beams with piezoelect... more In this paper, uncoupled thermopiezoelastic analysis of functionally graded beams with piezoelectric actuators subjected to electric field and thermal loading is studied using a higher order theory in conjunction with the variational approach. The material property of functionally graded core is assumed to vary according to the volume fraction of constituents given by exponential function. Linear temperature rise across the thickness is considered. The electromagnetic potential is assumed to be a piecewise linear across the each piezoelectric layer. The transverse displacement distribution across the thickness direction and the effect of geometry of beam on deflection is discussed in detail.

Journal of Solid Mechanics, Apr 30, 2009

ADMT Journal, Mar 1, 2020

Journal of Solid Mechanics, Jun 30, 2009

World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering, Aug 20, 2009

Journal of Solid Mechanics, Mar 1, 2018

Journal of Theoretical and Applied Mechanics, Jul 20, 2018

Zenodo (CERN European Organization for Nuclear Research), Dec 26, 2008

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Journal of Health Administration, 2018

Journal of Solid Mechanics, 2009

This paper studies free vibration of simply supported functionally graded beams with piezoelectri... more This paper studies free vibration of simply supported functionally graded beams with piezoelectric layers subjected to axial compressive loads. The Young's modulus of beam is assumed to be graded continuously across the beam thickness. Applying the Hamilton’s principle, the governing equation is established. Resulting equation is solved using the Euler’s Equation. The effects of the constituent volume fractions, the influences of applied voltage and axial compressive loads on the vibration frequency are presented. To investigate the accuracy of the present analysis, a compression study is carried out with a known data. © 2009 IAU, Arak Branch. All rights reserved.

Journal of Theoretical and Applied Mechanics, 2018