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Papers by Morteza Rajabpour

Damages in gas pipe lines and consequences of this faults have importance in gas industry. Some o... more Damages in gas pipe lines and consequences of this faults have importance in gas industry. Some of this consequence are explosion, fire, shut down of gas, economical cost and death of human. So prevent of every damage of gas pipe lines and repair incorrect pipes are very significant and can be effective role to prevention of accident. Utilize the appropriate coating method with nanocomposite is a new technique to prevent harm. Obviously, method of assembling appropriate coats is very important after repairing incorrect pipe. Usual method for repairing incorrect pipeline is shut off gas, cutting incorrect pipe and substitute new correct pipe with welding method and coat pipe with common cover (koltar). High cost, waste time, stress concentration in welding position and unsuitable consequences are disadvantages of this method. In this research new method with utilize nanocomposite material for repair damage positions suggested and analysed with FEM (Finite Element Method). For this purpose nanocomposite coats with different matrixes (polymer matrix and metal matrix) with different weight percentage (wt.%) and single wall carbon nano tube (SWCNT) as reinforce phase investigated. At last appropriate matrix, and weight percentage for repair damage pipe line gas selected. This method decrease the time of repair, economical cost and has high strength. Results show that nanocomposites have evident influence on improve strength of gas pipe. Result show that in every weight percentage (wt.%), nanocomposite has minimum stress and strength of this phase is better than other phases. Also appropriate weight percentage for nanocomposite that has minimum stress is 0.99% Epoxy and 0.01% SWCNT. Also Epoxy matrix has minimum stress in all phases respect to metal matrix.

Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanica... more Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanical, thermal and electrical properties. The applications of CNT, especially in composite materials, i.e. carbon nanotube reinforced polymer have received great attention and interest in recent years. To characterize the influence of CNT on the stress intensity factor of nanocomposites, three fracture modes (opening, shearing and tearing) are considered. The stress intensity factor of nanocomposites is evaluated using a representative volume element (RVE) based on the continuum mechanics and finite element method (FEM). Inter-atomic interactions of CNT are simulated by beam elements in the finite element (FE) model. Non-linear springbased line elements are employed to simulate the van der Waals (vdW) bonds. In all fracture modes, the stress intensity factor was determined for pure matrix and matrix reinforced with single-walled carbon nanotube (SWCNT). Numerical results indicate that the lo...

Science and Engineering of Composite Materials, 2014

Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanica... more Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanical, thermal, and electrical properties. In this research, a multiscale finite element analysis is proposed to study the interaction between nanotubes and matrix at the nanoscale near a crack tip. The influence of the chirality and length of single-walled CNT (SWCNTs) on the stress intensity factor of epoxy/SWCNT were studied. It was found that the chirality, length, and radius of CNT have significant effects on the stress intensity factor of nanocomposites. Multiscale simulations from macro to nano or the reverse improved specification of toughness mechanisms.

In this paper, the elastic moduli of elliptic single walled carbon nanotubes (ESWCNTs) are descri... more In this paper, the elastic moduli of elliptic single walled carbon nanotubes (ESWCNTs) are described. A three-dimensional finite element (FE) model for such carbon nanotubes is proposed. The covalent bonds are simulated by beam elements in the FE model. The elastic moduli of beam elements are ascertained from a linkage between molecular and continuum mechanics. The deformations of the FE model are subsequently used to predict the elastic moduli of ESWCNTs. In order to demonstrate the FE performance, the influence of length, chirality, diameter and cross sectional aspect ratios on the elastic moduli (Young's modulus and shear modulus) of ESWCNTs is investigated. It is found that the cross sectional aspect ratio of ESWCNTs significantly affects the elastic moduli. With increasing cross sectional aspect ratio, the Young's modulus and shear modulus decrease. As a result, every change in geometry operates as a defect and decreases the elastic moduli. With increasing the length, Young's modulus increases and the shear modulus decreases.

Fullerenes, Nanotubes and Carbon Nanostructures, 2014

ABSTRACT In this paper, the elastic moduli of defected, twisted, elliptic, bended and hetero-junc... more ABSTRACT In this paper, the elastic moduli of defected, twisted, elliptic, bended and hetero-junction carbon nanotubes (CNTs) are described. A three-dimensional finite element (FE) model of space-frame structure is proposed for these (CNTs). It is found that the torsional angle of twisted (CNTs), the cross sectional aspect ratio (a/b) of elliptic (CNTs), the bending angle of bended (CNTs) and the choice of the length and the chirality of hetero-junction carbon nanotubes (HJCNTs) significantly affect mechanical properties. The values of the Young's modulus have varied from 0.99 to 0.999 TPa for defected, 0.36 to 1.04 TPa for twisted, 0.87 to 1.04 TPa for elliptic, 0.95 to 1.04 for bended nanotubes and 0.96 to 1.27 TPa for HJCNTs. The results demonstrate that the proposed FE model is a valuable tool to study the mechanical behavior of HJCNTs and the deformed CNT. Different kinds of defects and deformations decrease the mechanical properties of CNTs.

Composites Part B: Engineering, 2013

A global-local multiscale finite element method (FEM) is proposed to study the interaction of nan... more A global-local multiscale finite element method (FEM) is proposed to study the interaction of nanotubes and matrix at the nanoscale near a crack tip. A 3D FE model of a representative volume element (RVE) in crack tip is built. The effects of the length and chirality of single walled carbon nanotube (SWCNT) in a polymer matrix on the fracture behavior were studied in the presence of van der Waals (vdW) interaction as inter-phase region. Detailed results show that with increasing the weight percentage of SWCNT, fracture toughness improves. Three situations of nanotube directions with respect to crack are considered. Results show that bridging condition has minimum stress intensity factor. In addition, it can be seen that the crack resistance improves by increasing the length and chirality for all kinds of nanotubes. Finally, epoxy/SWCNT 10 wt.% has lower stress intensity factor compared to epoxy/halloysite 10 wt.% in similar loading state.

In this paper, the elastic moduli of elliptic carbon nanotubes (ECNTs) are described. A three-dim... more In this paper, the elastic moduli of elliptic carbon nanotubes (ECNTs) are described. A three-dimensional finite element (FE) model for this carbon nanotube is proposed. The covalent bonds are simulated by beam elements in the FE model. It is found that the cross sectional aspect ratio (a/b) of ECNTs significantly affects Young's and shear modulus. Based on the FE model, the values of the Young's modulus have varied from 0.87 to 1.04 TPa and the values of the shear modulus have changed from 0.17 to 0.45 TPa.

ABSTRACT A multiscale analysis and finite element method are proposed to study the interaction of... more ABSTRACT A multiscale analysis and finite element method are proposed to study the interaction of nanotubes and matrix at the nano-scale near a crack tip. The effects of the length and chirality of single walled carbon nanotube (SWNT) in a polymer matrix in presence of van der Waals (vdW) interaction as inter-phase region on the fracture behavior were studied. It was found that the length and chirality has a significant effect on stress intensity factor of nanocomposites.

ABSTRACT In this paper, the influences of length and chirality on the Young’s modulus of hetero-j... more ABSTRACT In this paper, the influences of length and chirality on the Young’s modulus of hetero-junction carbon nanotubes (HJCNTs) are described. A three-dimensional finite element (FE) model for HJCNTs is proposed. The model development is based on the assumption that carbon nanotubes, when subjected to loading, behave like space-frame structures. The bonds between carbon atoms are considered as connecting load-carrying members, while the carbon atoms as joints of the members. The elastic moduli of beam elements are considered by using a linkage between molecular and continuum mechanics. Investigation includes two cases, variable length with constant chirality and variable chirality with constant length. It is found that the choice of length and chirality significantly affects the calculation of Young’s modulus. The results show that in the case of constant length, with increased chirality, the Young’s modulus of HJCNTs increases and in the case of constant chirality, with increased length, the Young’s modulus of HJCNTs decreases, but this decrease is weak. The presented results demonstrate that Young’s modulus of HJCNTs with chirality more than ((5, 5), (10, 10)), is larger than SWCNTs with same and larger chirality. The presented results demonstrate that the proposed FE model may provide a valuable tool for studying the mechanical behavior of hetero-junction carbon nanotubes (HJCNTs) and carbon nanotubes.

ABSTRACT Carbon nanotubes (CNTs) demonstrate unusually high stiffness, strength and resilience, a... more ABSTRACT Carbon nanotubes (CNTs) demonstrate unusually high stiffness, strength and resilience, and may become an ideal reinforcing material for new composites. This paper describes a finite element formulation that is appropriate for the numerical prediction of the mechanical behavior of polypropylene matrix nanocomposite. In current work it is assumed that the deformed cross sectional area of CNT is ellipse.Non-linear spring-based line elements are employed to simulate the vander Waals bonds. Elastic moduli of nanocomposites are evaluated using a representative volume element (RVE) based on the continuum mechanics and FEM.A significant enhancement in the stiffness of the polymer owing to the adding of the ECNTs is found. Addition of ECNTs in a matrix at a determined volume fraction can increase the stiffness of the composite.

Damages in gas pipe lines and consequences of this faults have importance in gas industry. Some o... more Damages in gas pipe lines and consequences of this faults have importance in gas industry. Some of this consequence are explosion, fire, shut down of gas, economical cost and death of human. So prevent of every damage of gas pipe lines and repair incorrect pipes are very significant and can be effective role to prevention of accident. Utilize the appropriate coating method with nanocomposite is a new technique to prevent harm. Obviously, method of assembling appropriate coats is very important after repairing incorrect pipe. Usual method for repairing incorrect pipeline is shut off gas, cutting incorrect pipe and substitute new correct pipe with welding method and coat pipe with common cover (koltar). High cost, waste time, stress concentration in welding position and unsuitable consequences are disadvantages of this method. In this research new method with utilize nanocomposite material for repair damage positions suggested and analysed with FEM (Finite Element Method). For this purpose nanocomposite coats with different matrixes (polymer matrix and metal matrix) with different weight percentage (wt.%) and single wall carbon nano tube (SWCNT) as reinforce phase investigated. At last appropriate matrix, and weight percentage for repair damage pipe line gas selected. This method decrease the time of repair, economical cost and has high strength. Results show that nanocomposites have evident influence on improve strength of gas pipe. Result show that in every weight percentage (wt.%), nanocomposite has minimum stress and strength of this phase is better than other phases. Also appropriate weight percentage for nanocomposite that has minimum stress is 0.99% Epoxy and 0.01% SWCNT. Also Epoxy matrix has minimum stress in all phases respect to metal matrix.

Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanica... more Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanical, thermal and electrical properties. The applications of CNT, especially in composite materials, i.e. carbon nanotube reinforced polymer have received great attention and interest in recent years. To characterize the influence of CNT on the stress intensity factor of nanocomposites, three fracture modes (opening, shearing and tearing) are considered. The stress intensity factor of nanocomposites is evaluated using a representative volume element (RVE) based on the continuum mechanics and finite element method (FEM). Inter-atomic interactions of CNT are simulated by beam elements in the finite element (FE) model. Non-linear springbased line elements are employed to simulate the van der Waals (vdW) bonds. In all fracture modes, the stress intensity factor was determined for pure matrix and matrix reinforced with single-walled carbon nanotube (SWCNT). Numerical results indicate that the lo...

Science and Engineering of Composite Materials, 2014

Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanica... more Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanical, thermal, and electrical properties. In this research, a multiscale finite element analysis is proposed to study the interaction between nanotubes and matrix at the nanoscale near a crack tip. The influence of the chirality and length of single-walled CNT (SWCNTs) on the stress intensity factor of epoxy/SWCNT were studied. It was found that the chirality, length, and radius of CNT have significant effects on the stress intensity factor of nanocomposites. Multiscale simulations from macro to nano or the reverse improved specification of toughness mechanisms.

In this paper, the elastic moduli of elliptic single walled carbon nanotubes (ESWCNTs) are descri... more In this paper, the elastic moduli of elliptic single walled carbon nanotubes (ESWCNTs) are described. A three-dimensional finite element (FE) model for such carbon nanotubes is proposed. The covalent bonds are simulated by beam elements in the FE model. The elastic moduli of beam elements are ascertained from a linkage between molecular and continuum mechanics. The deformations of the FE model are subsequently used to predict the elastic moduli of ESWCNTs. In order to demonstrate the FE performance, the influence of length, chirality, diameter and cross sectional aspect ratios on the elastic moduli (Young's modulus and shear modulus) of ESWCNTs is investigated. It is found that the cross sectional aspect ratio of ESWCNTs significantly affects the elastic moduli. With increasing cross sectional aspect ratio, the Young's modulus and shear modulus decrease. As a result, every change in geometry operates as a defect and decreases the elastic moduli. With increasing the length, Young's modulus increases and the shear modulus decreases.

Fullerenes, Nanotubes and Carbon Nanostructures, 2014

ABSTRACT In this paper, the elastic moduli of defected, twisted, elliptic, bended and hetero-junc... more ABSTRACT In this paper, the elastic moduli of defected, twisted, elliptic, bended and hetero-junction carbon nanotubes (CNTs) are described. A three-dimensional finite element (FE) model of space-frame structure is proposed for these (CNTs). It is found that the torsional angle of twisted (CNTs), the cross sectional aspect ratio (a/b) of elliptic (CNTs), the bending angle of bended (CNTs) and the choice of the length and the chirality of hetero-junction carbon nanotubes (HJCNTs) significantly affect mechanical properties. The values of the Young's modulus have varied from 0.99 to 0.999 TPa for defected, 0.36 to 1.04 TPa for twisted, 0.87 to 1.04 TPa for elliptic, 0.95 to 1.04 for bended nanotubes and 0.96 to 1.27 TPa for HJCNTs. The results demonstrate that the proposed FE model is a valuable tool to study the mechanical behavior of HJCNTs and the deformed CNT. Different kinds of defects and deformations decrease the mechanical properties of CNTs.

Composites Part B: Engineering, 2013

A global-local multiscale finite element method (FEM) is proposed to study the interaction of nan... more A global-local multiscale finite element method (FEM) is proposed to study the interaction of nanotubes and matrix at the nanoscale near a crack tip. A 3D FE model of a representative volume element (RVE) in crack tip is built. The effects of the length and chirality of single walled carbon nanotube (SWCNT) in a polymer matrix on the fracture behavior were studied in the presence of van der Waals (vdW) interaction as inter-phase region. Detailed results show that with increasing the weight percentage of SWCNT, fracture toughness improves. Three situations of nanotube directions with respect to crack are considered. Results show that bridging condition has minimum stress intensity factor. In addition, it can be seen that the crack resistance improves by increasing the length and chirality for all kinds of nanotubes. Finally, epoxy/SWCNT 10 wt.% has lower stress intensity factor compared to epoxy/halloysite 10 wt.% in similar loading state.

In this paper, the elastic moduli of elliptic carbon nanotubes (ECNTs) are described. A three-dim... more In this paper, the elastic moduli of elliptic carbon nanotubes (ECNTs) are described. A three-dimensional finite element (FE) model for this carbon nanotube is proposed. The covalent bonds are simulated by beam elements in the FE model. It is found that the cross sectional aspect ratio (a/b) of ECNTs significantly affects Young's and shear modulus. Based on the FE model, the values of the Young's modulus have varied from 0.87 to 1.04 TPa and the values of the shear modulus have changed from 0.17 to 0.45 TPa.

ABSTRACT A multiscale analysis and finite element method are proposed to study the interaction of... more ABSTRACT A multiscale analysis and finite element method are proposed to study the interaction of nanotubes and matrix at the nano-scale near a crack tip. The effects of the length and chirality of single walled carbon nanotube (SWNT) in a polymer matrix in presence of van der Waals (vdW) interaction as inter-phase region on the fracture behavior were studied. It was found that the length and chirality has a significant effect on stress intensity factor of nanocomposites.

ABSTRACT In this paper, the influences of length and chirality on the Young’s modulus of hetero-j... more ABSTRACT In this paper, the influences of length and chirality on the Young’s modulus of hetero-junction carbon nanotubes (HJCNTs) are described. A three-dimensional finite element (FE) model for HJCNTs is proposed. The model development is based on the assumption that carbon nanotubes, when subjected to loading, behave like space-frame structures. The bonds between carbon atoms are considered as connecting load-carrying members, while the carbon atoms as joints of the members. The elastic moduli of beam elements are considered by using a linkage between molecular and continuum mechanics. Investigation includes two cases, variable length with constant chirality and variable chirality with constant length. It is found that the choice of length and chirality significantly affects the calculation of Young’s modulus. The results show that in the case of constant length, with increased chirality, the Young’s modulus of HJCNTs increases and in the case of constant chirality, with increased length, the Young’s modulus of HJCNTs decreases, but this decrease is weak. The presented results demonstrate that Young’s modulus of HJCNTs with chirality more than ((5, 5), (10, 10)), is larger than SWCNTs with same and larger chirality. The presented results demonstrate that the proposed FE model may provide a valuable tool for studying the mechanical behavior of hetero-junction carbon nanotubes (HJCNTs) and carbon nanotubes.

ABSTRACT Carbon nanotubes (CNTs) demonstrate unusually high stiffness, strength and resilience, a... more ABSTRACT Carbon nanotubes (CNTs) demonstrate unusually high stiffness, strength and resilience, and may become an ideal reinforcing material for new composites. This paper describes a finite element formulation that is appropriate for the numerical prediction of the mechanical behavior of polypropylene matrix nanocomposite. In current work it is assumed that the deformed cross sectional area of CNT is ellipse.Non-linear spring-based line elements are employed to simulate the vander Waals bonds. Elastic moduli of nanocomposites are evaluated using a representative volume element (RVE) based on the continuum mechanics and FEM.A significant enhancement in the stiffness of the polymer owing to the adding of the ECNTs is found. Addition of ECNTs in a matrix at a determined volume fraction can increase the stiffness of the composite.