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A different approach to estimate the process parameters in tube hydroforming
, Article International Journal of Material Forming ; Volume 8, Issue 3 , July , 2015 , pp 355-366 ; ISSN: 19606206 ; Shirin, M. B ; Einolghozati, M ; Assempour, A ; Sharif University of Technology
Abstract
An enhanced unfolding inverse finite element method (IFEM) has been used together with an extended strain-based forming limit diagram (FLD) to develop a fast approach to predict the feasibility of tube hydroforming process of concept part and determine where the failure or defects can occur. In tube hydroforming, the inverse IFEM has been used for estimating the initial length of tube, axial feeding and fluid pressure. The already developed IFEM algorithm used in this study is based on the total deformation theory of plasticity. Although the nature of tube hydroforming is three-dimensional deformation, in this article a modeling technique has been used to perform the computations in...
Synthesis, characterization, electrochemical and solvatochromic investigations of novel monomeric and polymeric vanadyl schiff-base complexes
, Article Journal of Coordination Chemistry ; Volume 60, Issue 9 , 2007 , Pages 973-983 ; 00958972 (ISSN) ; Bezaatpour, A ; Behzad, M ; Sharif University of Technology
2007
Abstract
This article describes the synthesis and characterization of oxovanadium(IV) complexes containing tetradentate Schiff-base ligands derived from condensation of ethylenediamine, meso-1,2-diphenyl-1,2-ethylenediamine, 1,2-orthophenylenediamine and 1,2-cyclohexanediamine with 5-bromo-3-nitro-2- hydroxybenzaldehyde. The novel VOL1:[VO(5-Br-3-NO2salen)], VOL2:[VO(5-Br-3-NO2saloph)] and VOL3:[VO(5-Br- 3-NO2salchxn)] complexes were obtained in orange polymeric form with (V=O) stretching bands at 878, 884 and 884 cm-1, respectively, but the VOL4 complex was obtained as a green monomer with (V=O) stretching band at 978 cm-1. The redox process in acetonitrile was reversible for VOL4 and E° was...
Quadratic Forms and u-invariant
, M.Sc. Thesis Sharif University of Technology ; Gholamzadeh Mahmoudi, Mohammad (Supervisor)
Abstract
For a field of characteristic not two, the classical u-invariant is defined as the maximal dimension of anisotropic quadratic forms over F. Initially Kaplansky conjectured that u(F), when finite, is always a 2-power. Later Merkurjev constructed a field F such that u(F) = 6. This dissertation examines in detail the article: R. Elman, T. Y. Lam, Quadratic forms and the u-invariant. I. Math. Z. 131, 283-304 (1973). in which the notion of ”generalized u-invariant” (motivated by Pfister’s Local-Global Principle) was defined as the maximal dimension of anisotropic torsion quadratic forms over F. This is indeed a right generalization of the definition of the classical u-invariant since it not only...
On hyperbolic clifford algebras with involution
, Article Algebra Colloquium ; Volume 20, Issue 2 , 2013 , Pages 251-260 ; 10053867 (ISSN) ; Sharif University of Technology
2013
Abstract
The aim of this article is to provide a characterization of quadratic forms of low dimension such that the canonical involutions of their Clifford algebras are hyperbolic
Hyperbolic involutions and quadratic extensions
, Article Communications in Algebra ; Volume 39, Issue 1 , Jan , 2011 , Pages 125-132 ; 00927872 (ISSN) ; Sharif University of Technology
Abstract
This is a variation on a theme of Bayer-Fluckiger, Shapiro, and Tignol related to hyperbolic involutions. More precisely, criteria for the hyperbolicity of involutions of quadratic extensions of simple algebras and involutions of the form σ ⊗ τ and σ ⊗ ρ, where σ is an involution of a central simple algebra A, τ is the nontrivial automorphism of a quadratic extension of the center of A, and ρ is an involution of a quaternion algebra are obtained
Inclusion matrices and chains
, Article Journal of Combinatorial Theory. Series A ; Volume 115, Issue 5 , 2008 , Pages 878-887 ; 00973165 (ISSN) ; Khosrovshahi, G. B ; Maysoori, Ch ; Mohammad Noori, M ; Sharif University of Technology
2008
Abstract
Given integers t, k, and v such that 0 ≤ t ≤ k ≤ v, let Wt k (v) be the inclusion matrix of t-subsets vs. k-subsets of a v-set. We modify slightly the concept of standard tableau to study the notion of rank of a finite set of positive integers which was introduced by Frankl. Utilizing this, a decomposition of the poset 2[v] into symmetric skipless chains is given. Based on this decomposition, we construct an inclusion matrix, denoted by Wover(t, -) k (v), which is row-equivalent to Wt k (v). Its Smith normal form is determined. As applications, Wilson's diagonal form of Wt k (v) is obtained as well as a new proof of the well-known theorem on the necessary and sufficient conditions for...
On totally decomposable algebras with involution in characteristic two
, Article Journal of Algebra ; Volume 451 , 2016 , Pages 208-231 ; 00218693 (ISSN) ; Nokhodkar, A. H ; Sharif University of Technology
Abstract
A necessary and sufficient condition for a central simple algebra with involution over a field of characteristic two to be decomposable as a tensor product of quaternion algebras with involution, in terms of its Frobenius subalgebras, is given. It is also proved that a bilinear Pfister form, recently introduced by A. Dolphin, can classify totally decomposable central simple algebras of orthogonal type
On Hermitian Pfister forms
, Article Journal of Algebra and its Applications ; Volume 7, Issue 5 , 2008 , Pages 629-645 ; 02194988 (ISSN) ; Lequeu, E ; Gholamzadeh Mahmoudi, M ; Sharif University of Technology
2008
Abstract
Let K be a field of characteristic different from 2. It is known that a quadratic Pfister form over K is hyperbolic once it is isotropic. It is also known that the dimension of an anisotropic quadratic form over K belonging to a given power of the fundamental ideal of the Witt ring of K is lower bounded. In this paper, weak analogues of these two statements are proved for hermitian forms over a multiquaternion algebra with involution. Consequences for Pfister involutions are also drawn. An invariant uα of K with respect to a nonzero pure quaternion of a quaternion division algebra over K is defined. Upper bounds for this invariant are provided. In particular an analogue is obtained of a...
The effect of the imposed boundary rate on the formability of strain rate sensitive sheets using the M-K Method
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 9 , April , 2013 , Pages 2522-2527 ; 10599495 (ISSN) ; Ghazanfari, A ; Abrinia, K ; Assempour, A ; Sharif University of Technology
2013
Abstract
In spite of the fact that the experimental results indicate the significant effect of strain rate on forming limits of sheets, this effect is neglected in all theoretical methods of prediction of Forming Limit Diagrams (FLDs). The purpose of this paper is to modify the most renowned theoretical method of determination of FLDs (e.g., M-K model) so as to enable it to take into account the effect of strain rate. To achieve this aim, the traditional assumption of preexistence of an initial geometrical inhomogeneity in the sheet has been replaced with the assumption of a preexisting "material" inhomogeneity. It has been shown that using this assumption, the strain rate would not be omitted from...
Forming limit diagrams of ground St14 steel sheets with different thicknesses
, Article SAE International Journal of Materials and Manufacturing ; Volume 5, Issue 1 , 2012 , Pages 60-64 ; 19463979 (ISSN) ; Ghazanfari, A ; Abrinia, K ; Assempour, A ; Sharif University of Technology
2012
Abstract
The influence of sheet thickness on sheet metal forming limits is a controversial issue; while some investigations indicate the considerable influence of thickness on forming limit diagrams (FLDs), others suggest that it is of negligible importance. In the present work, it has been demonstrated that if the thickness-reduction process is chosen so as not to alter the micro structure of the material, the forming limits do not change with variations of thickness. A material which has extensive usage in sheet metal forming processes of automotive industry (St14) has been provided. The initial thickness of the sheet is 1.5mm and using grinding process (which does not alter the microstructure) the...
Involutions of a clifford algebra induced by involutions of orthogonal group in characteristic 2
, Article Communications in Algebra ; Volume 43, Issue 9 , Jun , 2015 , Pages 3898-3919 ; 00927872 (ISSN) ; Nokhodkar, A. H ; Sharif University of Technology
Taylor and Francis Inc
2015
Abstract
Among the involutions of a Clifford algebra, those induced by the involutions of the orthogonal group are the most natural ones. In this work, several basic properties of these involutions, such as the relations between their invariants, their occurrences, and their decompositions, are investigated
Forming limit diagram of tubular hydroformed parts considering the through-thickness compressive normal stress
, Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 230, Issue 1 , 2016 , Pages 332-343 ; 14644207 (ISSN) ; Abri Nia, K ; Assem Pour, A ; Khakpour Nejadkhaki, H ; Shahbazi Mastan Abad, A ; Sharif University of Technology
SAGE Publications Ltd
Abstract
In this study, the effect of a compressive normal stress has been considered in the determination of forming limit diagrams and forming limit stress diagrams to predict neck initiation failure in tube hydroforming of T-shaped parts. Computation of the forming limit diagrams and FLSDs is based on the generalized Marciniak and Kuczynski method to consider the existence of through-thickness compressive normal stress. The proposed forming limit diagrams and FLSDs were used in conjunction with ABAQUS/EXPLICIT finite element simulations to predict the onset of necking in tube hydroforming of T-shaped part. The amount of calibration pressure and axial feeding required to produce an acceptable part...
Formability of friction stir-welded blanks with different thickness ratios
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 47, Issue 5 , 2016 , Pages 2177-2187 ; 10735623 (ISSN) ; Ghaffarpour, M ; Habibi, N ; Kokabi, A. H ; Akbarzadeh, A ; Sharif University of Technology
Springer Boston
Abstract
Welded sheets with different thicknesses are one of the interesting types of tailor-welded blanks (TWBs) that are widely used in metal-forming industries. In the present work, the formability behavior of different 1100-aluminum TWBs was studied. In this regard, the TWBs were made with different thickness ratios by using friction stir welding (FSW) at different welding rotational speeds (ω). The thickness ratios of 1.0, 1.3, and 1.7 were investigated where the thinner sheets had 1.5 mm thick for all conditions; i.e., the volume of welded material increased when the thickness ratio increased. Macrostructural observations, mechanical investigations, and sheet-forming limit tests were...
Forming limit diagrams by including the M–K model in finite element simulation considering the effect of bending
, Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 232, Issue 8 , 2018 , Pages 625-636 ; 14644207 (ISSN) ; Hashemi, R ; Ghazanfari, A ; Naghdabadi, R ; Assempour, A ; Sharif University of Technology
SAGE Publications Ltd
2018
Abstract
Forming limit diagram is often used as a criterion to predict necking initiation in sheet metal forming processes. In this study, the forming limit diagram was obtained through the inclusion of the Marciniak–Kaczynski model in the Nakazima out-of-plane test finite element model and also a flat model. The effect of bending on the forming limit diagram was investigated numerically and experimentally. Data required for this simulation were determined through a simple tension test in three directions. After comparing the results of the flat and Nakazima finite element models with the experimental results, the forming limit diagram computed by the Nakazima finite element model was more convenient...
Design of landmark pedestrian urban bridge with evolutionary topology optimization
, Article 7th Annual International Conference on Architecture and Civil Engineering, ACE 2019, 27 May 2019 through 28 May 2019 ; 2019 , Pages 100-120 ; 2301394X (ISSN) ; Aliakbarlou, H ; Khoraskani, R. A ; Hafezi, M ; Sharif University of Technology
Global Science and Technology Forum
2019
Abstract
one of the important issues of construction industry today, is providing a meaningful interconnectivity between Architecture and its technical and technological aspects. In construction projects aesthetic and form is habitually crucial for the architect while structural designers aim for efficiency and stability of the structure. This research is concerned with the design of an urban footbridge located in Tehran-Iran with social and cultural spaces in which the form of the bridge is obtained by the use of topology optimization process. The objective of this study is to investigate the utilization of topology optimization process in architecture in order to achieve a beneficial design...
Design of landmark pedestrian urban bridge with evolutionary topology optimization
, Article 7th Annual International Conference on Architecture and Civil Engineering, ACE 2019, 27 May 2019 through 28 May 2019 ; 2019 , Pages 100-120 ; 2301394X (ISSN) ; Aliakbarlou, H ; Afghani Khoraskani, R ; Hafezi, M ; Anderson M. S. T ; Anderson P. C. O ; Sharif University of Technology
Global Science and Technology Forum
2019
Abstract
one of the important issues of construction industry today, is providing a meaningful interconnectivity between Architecture and its technical and technological aspects. In construction projects aesthetic and form is habitually crucial for the architect while structural designers aim for efficiency and stability of the structure. This research is concerned with the design of an urban footbridge located in Tehran-Iran with social and cultural spaces in which the form of the bridge is obtained by the use of topology optimization process. The objective of this study is to investigate the utilization of topology optimization process in architecture in order to achieve a beneficial design...
A hypoelasto-plastic finite strain simulation of powder compaction processes with density-dependent endochronic model
, Article International Journal of Solids and Structures ; Volume 41, Issue 22-23 , 2004 , Pages 6081-6110 ; 00207683 (ISSN) ; Bakhshiani, A ; Sharif University of Technology
2004
Abstract
In this paper, a new approach is developed based on an endochronic density-dependent plasticity model for describing the isothermal deformation behavior of metal powder at low homologous temperature. As large deformations are observed in powder compaction processes, the endochronic constitutive model is presented based on large strain plasticity and an integration scheme is established for the rate constitutive equations. Endochronic constitutive equations are established based on coupling between deviatoric and hydrostatic behavior. The elastic response is stated in term of hypoelastic model and endochronic constitutive equations are stated in unrotated frame of reference. Finally, the...
An endochronic plasticity model for numerical simulation of industrial powder compaction processes
, Article Communications in Numerical Methods in Engineering ; Volume 19, Issue 7 , 2003 , Pages 521-534 ; 10698299 (ISSN) ; Bakhshiani, A ; Mofid, M ; Sharif University of Technology
2003
Abstract
In this paper, the numerical modelling of powder forming process is simulated by a finite element analysis using an endochronic plasticity model. A general algorithm for the endochronic theory from the viewpoint of efficient numerical modelling is presented. Constitutive equations are established based on coupling between deviatoric and hydrostatic behaviour to the endochronic theory. Finally, the numerical schemes are examined for efficiency in the modelling of a rotational flanged-component. It is shown how the endochronic plasticity describes the behaviour of powder material from the initial stage of compaction to final stage, in which material behaves as solid metals. © 2003 John Wiley...
An endochronic plasticity model for powder compaction processes
, Article Journal of Materials Processing Technology ; Volume 125-126 , 2002 , Pages 138-143 ; 09240136 (ISSN) ; Khoei, A. R ; Mofid, M ; Sharif University of Technology
2002
Abstract
In this paper, the numerical modelling of the powder forming process is simulated by a finite element analysis using a density-dependent endochronic plasticity model. An endochronic constitutive model based on large strain plasticity is presented. The elastic response is stated in term of a hypoelastic model and endochronic plasticity constitutive equations are stated in the unrotated frame of reference. A general algorithm for the endochronic theory from the viewpoint of efficient numerical modelling is presented. Constitutive equations of the endochronic theory in large strain state and their numerical integration are established. An algorithmic modulus consistent with numerical...
Dynamic modeling and structural reliability of an aeroelastic launch vehicle
, Article Advances in Aircraft and Spacecraft Science ; Volume 9, Issue 3 , 2022 , Pages 263-M278 ; 2287528X (ISSN) ; Khodabaksh, A. H ; Sharif University of Technology
Techno-Press
2022
Abstract
The time-varying structural reliability of an aeroelastic launch vehicle subjected to stochastic parameters is investigated. The launch vehicle structure is under the combined action of several stochastic loads that include aerodynamics, thrust as well as internal combustion pressure. The launch vehicle's main body structural flexibility is modeled via the normal mode shapes of a free-free Euler beam, where the aerodynamic loadings on the vehicle are due to force on each incremental section of the vehicle. The rigid and elastic coupled nonlinear equations of motion are derived following the Lagrangian approach that results in a complete aeroelastic simulation for the prediction of the...