| 1. |
- Atashipour, Seyed Rasoul, et al.
(author)
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Elastic analysis of thick-walled pressurized spherical vessels coated with functionally graded materials
- 2014
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In: Meccanica. - : Springer Science and Business Media LLC. - 1572-9648 .- 0025-6455. ; 49:12, s. 2965-2978
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Journal article (peer-reviewed)abstract
- In recent years, functionally graded material (FGM) has been widely explored in coating technology amongst both academic and industry communities. FGM coatings are suitable substitutes for many typical conventional coatings which are susceptible to cracking, debonding and eventual functional failure due to the mismatch of material properties at the coating/substrate interface. In this study, a thick spherical pressure vessel with an inner FGM coating subjected to internal and external hydrostatic pressure is analyzed within the context of three-dimensional elasticity theory. Young’s modulus of the coating is assumed to vary linearly or exponentially through the thickness, while Poisson’s ratio is considered as constant. A comparative numerical study of FGM versus homogeneous coating is conducted for the case of vessel under internal pressure, and the dependence of stress and displacement fields on the type of coating is examined and discussed.
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| 2. |
- Nilsson, Peter, 1982, et al.
(author)
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The impact of production-dependent geometric properties on fatigue-relevant stresses in laser-welded corrugated core steel sandwich panels
- 2019
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In: Welding in the World. - : Springer Verlag. - 0043-2288 .- 1878-6669. ; 62:6, s. 1801-1818
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Journal article (peer-reviewed)abstract
- For bridge deck applications, laser-welded corrugated core steel sandwich panels with dual weld lines per crest and trough have been shown to be highly material- and economically efficient. The nature of welding induces a variation in the geometric properties of the joint that connects the core to the faces. The geometric properties of the joint are the weld width, weld misalignment, and plate gap between the core and the faces. This paper aims to investigate the impact of the variation of the production-dependent geometric properties of the joint on the fatigue-relevant stresses. A secondary aim of this paper is to investigate the impact of contact between the core and the faces on the weld region stresses. Within this paper, the production of four sandwich panels is documented and the manufacturing-dependent geometric properties of their joints are quantified. In order to investigate the impact of the natural variation of the parameters, a parametric study based on finite element analyses is executed. The result of the parametric study shows, among several other findings, that misalignment of the weld line in relation to the core direction can lead to considerable increases in stresses, determinant for the fatigue life of the panel.
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| 3. |
- Atashipour, Seyed Rasoul, et al.
(author)
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On the Shear Buckling of Clamped Narrow Rectangular Orthotropic Plates
- 2015
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In: Mathematical problems in engineering (Print). - : Hindawi Limited. - 1024-123X .- 1563-5147. ; 2015
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Journal article (peer-reviewed)abstract
- This paper deals with stability analysis of clamped rectangular orthotropic thin plates subjected to uniformly distributed shear load around the edges. Due to the nature of this problem, it is impossible to present mathematically exact analytical solution for the governing differential equations. Consequently, all existing studies in the literature have been performed by means of different numerical approaches. Here, a closed-form approach is presented for simple and fast prediction of the critical buckling load of clamped narrow rectangular orthotropic thin plates. Next, a practical modification factor is proposed to extend the validity of the obtained results for a wide range of plate aspect ratios. To demonstrate the efficiency and reliability of the proposed closed-form formulas, an accurate computational code is developed based on the classical plate theory (CPT) by means of differential quadrature method (DQM) for comparison purposes. Moreover, several finite element (FE) simulations are performed via ANSYS software. It is shown that simplicity, high accuracy, and rapid prediction of the critical load for different values of the plate aspect ratio and for a wide range of effective geometric and mechanical parameters are the main advantages of the proposed closed-form formulas over other existing studies in the literature for the same problem.
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| 4. |
- Atashipour, Seyed Rasoul
(author)
-
Structural Analysis of Deep Composite Box-Type Components with application to a proprietary stabilising timber wall element
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- The stabilising wall element of the Trä8-system is a deep box-type beam/column element which is made of different types of timber composites including framing members of gluedlaminated timber (glulam) and sheathings of laminated veneer lumber (LVL). This element is used as a ―shear wall‖ in multi-storey buildings up to four storeys. To be able to optimise thecomposite stabilising element and use its maximum potential and efficiency, it is necessary to have sufficient fundamental knowledge and information about the structural behaviour and influences of different mechanical properties and geometrical parameters and dimensions of the sub-elements.In this thesis, structural analysis and design principles of the Trä8 stabilising wall element are discussed, including the early stage of erection during assembly to the final usage and residence. A list of required fundamental basic analyses are presented, including accurate deflection analysis for the serviceability limit state, local pre- and post-buckling of the LVL sheathings, global buckling as well as the lateral-torsional buckling of the stabilising element in different design situations. This thesis is then focused on deformations and local instability. For each type of structural problem, accurate, but simple and general methodology is employed to incorporate a large number of effective geometric and property parameters. In this way, a fast evaluation of the influence of different parameters is possible for a wide range of values without needing several time-consuming 3-D finite element (FE) simulations. In several cases, the accuracy and validity of the obtained solutions and formulae are examined and confirmed by comparing their results to those based on the 3-D FE simulations. First, different composite beam theories including shear effects are employed for deflection analysis of the stabilising timber element. Next, an accurate energy-based methodology isdeveloped rendering an explicit formula that gives accurate predictions for the deflection of the stabilising element within a medium range of sheathing or web thicknesses and/or stiffnesses. For weak shear webs, however, this model is not sufficient. Therefore, another new model based on the partial composite interaction theory is developed for accurate deflection predictions of the element having weak shear webs. This model contains simple but accurate formulae for deflection analysis of any similar composite box-type of element with an arbitrary range of geometry and property parameters.Next, shear buckling of the rectangular LVL-panel between the framing members are analysed using differential quadrature (DQ) numerical technique as well as an explicit analytical solution and a formula is established for accurate and fast prediction of the shear pre-buckling of the LVL. This study is extended by considering the effect of each individual lamina of the LVL as well as general orthotropic material properties using a laminated theoryand the DQ solution approach. Further, the post-buckling of the LVL panel is studied based on a simple analytical method with rotating stress fields together with the accurate 3-D FE simulations. A simple formula is then proposed for accurate prediction of the shear post-buckling resistance of the LVL-panel in the stabilising element. As a result of the thesis concerning the two main focus areas, deformations and local instability, explicit analytical formulae are presented for the design of the box-type stabilisingelement with respect to deflections including shear effects in the serviceability limit state and with respect to local shear buckling of the sheathings of the stabilising element including the post-critical area in the ultimate limit state.
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| 5. |
- Atashipour, Seyed Rasoul, et al.
(author)
-
The Effect of Weak Shear Webs on the Deformations of Timber Box Type Beams
- 2015
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In: Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing. - Stirlingshire : Civil-Comp Press.
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Conference paper (peer-reviewed)abstract
- This paper deals with deflection analysis of a deep composite box beam due to inplane shear deformations, especially the modelling of the shear deformations in the webs is considered. The beam is composed of three framing members with sheathings on both sides. The sheathings or webs between the framing members are modelled as shear media with equivalent slip moduli corresponding to the partially composite beam model with three separated layers and two interlayer slip areas. The minimum total potential energy principle is employed to obtain the governing equilibrium equations and corresponding boundary conditions. The coupled set of governing equations is recast into an uncoupled form and solved explicitly together with the corresponding boundary conditions. The closed-form solutions obtained are compared to those based on the conventional beam theories. It is shown that the model is capable of predicting accurately the deflections for a wide range of geometry and property parameters, especially for small shear stiffness (slip modulus) values for the webs. The formula for the deflection is reduced to the Timoshenko formula for full composite interaction when the shear slip modulus of the web approaches infinity. Comparative numerical results are presented to show the influence of bending deformations, shear deformations in the framing layers and the in-plane shear deformations in the sheathings.
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| 6. |
- Girhammar, Ulf Arne, et al.
(author)
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A study on shear deformations of deep composite box-Type beams used in timber building structures
- 2013
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In: Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, 3-6 September 2013, Cagliari, Sardinia, Italy. - Stirlingshire : Civil-Comp Press. - 9781905088577
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Conference paper (peer-reviewed)abstract
- The higher-order shear deformation beam theory of Reddy-Bickford predicts accurately the shear deflection without the need of a shear correction factor. However, for more complicated cross-sections, e.g. including holes, it is shown that this theory is not adequate. To be able to predict accurately the shear deflections of deep composite box-type cross-sectional beams, a simple engineering approach is used to derive a closed-form expression for the shear correction factor for those types of beams. The high accuracy and reliability of the developed procedure is demonstrated by comparing those results with accurate three-dimensional finite element results and with Timoshenko and Reddy-Bickford theories. A comprehensive parametric study is presented to investigate the effects of various mechanical properties and geometric dimensions of the box-type of beams for the various models. There is very good agreement between the proposed engineering method and the three-dimensional finite element model
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| 7. |
- Hosseini-Hashemi, Sh., et al.
(author)
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Accurate free vibration analysis of thick laminated circular plates with attached rigid core
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:25, s. 5581-5596
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Journal article (peer-reviewed)abstract
- This paper deals with the free vibration behavior of laminated transversely isotropic circular plates with axisymmetric rigid core attached at the center. The governing equations of motion are obtained based on Mindlin's first-order shear deformation plate theory. Two possible categories of vibration modes related to up-down translation of the core and wobbly rotation of the core about a diameter are studied. Accurate natural frequencies hitherto not reported in the literature are presented for a wide range of thickness-to-radius ratio, inner-to-outer radius ratio, mass and moment of inertia ratios of the core and various boundary conditions at the outer edge of the plate. Numerical results are compared with those of a three-dimensional finite element method (3-D FEM) to demonstrate the high accuracy and reliability of the current analysis.
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| 8. |
- Hosseini-Hashemi, Sh., et al.
(author)
-
Free vibration analysis of functionally graded elliptical plates
- 2012
-
In: International journal of Maritime Technology. - 2345-6000. ; 8:15, s. 43-60
-
Journal article (peer-reviewed)abstract
- This paper deals with a free vibration analysis of functionally graded elliptical plates with different classical boundary conditions on the basis of polynomial-Ritz method and classical plate theory. The proposed admissible function is capable to obtain accurate natural frequencies of various classical boundary conditions namely, clamped, free and simply supported edges. The mechanical properties of the FG plate are assumed to vary continuously through the thickness of the plate and obey a power law distribution of the volume fraction of the constituents. The convergency of applied polynomial-Ritz method is investigated. In order to verify the accuracy of the present solution, a comprehensive comparison study is performed with the available results in the literature for homogeneous elliptical plate and FG circular plate. Also, the numerical results of the present solution for FG elliptical plate are compared with those of the finite element method (FEM). Finally, the effects of the plate geometry and inhomogeneity on the natural frequencies are investigated and some vibrational mode shapes related to symmetric-symmetric, symmetric-antisymmetric, antisymmetric- symmetric and antisymmetric- antisymmetric states are presented.
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| 9. |
- Nasr, A., et al.
(author)
-
An elasticity solution for static analysis of functionally graded curved beam subjected to a shear force
- 2010
-
In: International Journal of Engineering. Transactions B: Applications. - 1728-144X. ; 23, s. 169-178
-
Journal article (peer-reviewed)abstract
- In this paper, using 2-D theory of elasticity, a closed-form solution is presented for stress distributions and displacements of a FG curved beam under shear force at its free end. The material properties are assumed to vary continuously through the radial direction based on a simple power law model and Poisson’s ratio is supposed to be constant. In order to verify the solution, it is shown that allstress and displacement relations are converted to those of a homogenous curved beam when the inhomogeneity constant approaches zero. The effects of inhomogeneity on stress distributions are investigated. It is shown that specified stress distribution profiles can be obtained by changing the variation of volume fraction of constituents. It is observed that for a specific value of inhomogeneity constant, a proper stress distribution along the radial direction is obtained for designing purposes.
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| 10. |
- Saidi, A., et al.
(author)
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Analytical solution of free vibration of thick transversely isotropic rectangular plates, based on first order shear deformation theory
- 2009
-
In: Aerospace Mechanics Journal. ; 4, s. 59-69
-
Journal article (peer-reviewed)abstract
- In this paper, a reformulation for equations of motion for transversely isotropic plates has been obtained based on first shear deformation theory. Unlike the three coupled original equations, this new reformulation consists of two decoupled partial differential equations which can be solved much easier. For free vibration analysis of transversely isotropic plates, the mentioned equations have been solved for two cases. In the first case, using double Fourier series, closed-form solution has been achieved for natural frequencies of simply supported plates. In the second case, free vibration of a plate with arbitrary boundary conditions in two parallel edges has been considered. In order to satisfy the arbitray boundary conditions, some relations have been presented for unknown functions of the original system of equations in terms of the unknowns of the decoupled equations. Finally, numerical results for six possible cases of classical boundary conditions have been presented. Besides, some important results of the presented analysis have been presented for transversely isotropic plates. The results show that despite of the small differences between the natural frequencies of the thin isotropic and transversely isotropic plates, the differences are more significant for the natural frequencies of the thick plate. Also, effects of increasing thickness on the value of natural frequencies for transversely isotropic plates are more than the isotropic ones.
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