| 1. |
- Atashipour, Seyed Rasoul, et al.
(författare)
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Elastic analysis of thick-walled pressurized spherical vessels coated with functionally graded materials
- 2014
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Ingår i: Meccanica. - : Springer Science and Business Media LLC. - 1572-9648 .- 0025-6455. ; 49:12, s. 2965-2978
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Welding in the World. - : Springer Verlag. - 0043-2288 .- 1878-6669. ; 62:6, s. 1801-1818
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Tidskriftsartikel (refereegranskat)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. |
- Sburlati, R., et al.
(författare)
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Exact elastic analysis of a doubly coated thick circular plate using functionally graded interlayers
- 2015
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Ingår i: Archive of Applied Mechanics. - : Springer Science and Business Media LLC. - 0939-1533 .- 1432-0681. ; 85:12, s. 1779-1792
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Tidskriftsartikel (refereegranskat)abstract
- Development of new coating systems has been an important issue over the years with the motivation of extending the effective life of mechanical elements. For this intent, functionally graded materials have been recently used in a variety of applications as promising replacements for conventional coatings. In the present study, a hybrid coating system taking advantage of graded composition concept is proposed to enhance the through-thickness stress distribution within a double-sided coated circular thick homogeneous plate. The coating system is composed of two main layers: an external homogeneous layer and an interlayer between the external layer and the plate, with graded material composition. All layers are modeled within the context of three-dimensional elasticity theory, and an elasto-static solution is obtained by using suitable potential functions. Accuracy and reliability of the proposed analysis is investigated by comparison with results obtained in the literature, as well as with the results of a three-dimensional finite element simulation. Comparative study shows the inherent advantages of the present hybrid coating system over the conventional homogeneous coating or the functionally graded coating layers.
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| 4. |
- Sburlati, R., et al.
(författare)
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Reduction of the stress concentration factor in a homogeneous panel with hole by using a functionally graded layer
- 2014
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Ingår i: Composites Part B: Engineering. - : Elsevier BV. - 1359-8368 .- 1879-1069. ; 61, s. 99-109
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Tidskriftsartikel (refereegranskat)abstract
- This work aims at understanding the effect of a radially heterogeneous layer around the hole in a homogeneous plate on the stress concentration factor. The problem concerns a single hole in a plate under different far-field in-plane loading conditions. By assuming a radial power law variation of Young's modulus and constant value for Poisson's ratio, the governing differential equations for plane stress conditions, and general in-plane loading conditions are studied. The elastic solutions are obtained in closed form and, in order to describe localized interface damage between the ring and the plate, two different interface conditions (perfectly bonded and frictionless contact) are studied. The formulae for the stress concentration factors are explicitly given for uniaxial, biaxial and shear in-plane loading conditions and comparisons with interface hoop stress values are performed. The solutions are investigated to understand the role played by the geometric and graded constitutive parameters. The results are validated with numerical finite element simulations in which some simplified hypotheses assumed in the analytical model, are relaxed to explore the range of validity of the elastic solution presented. In this way the results obtained are useful in tailoring the parameters for specific applications.
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| 5. |
- Atashipour, Rasoul, 1983, et al.
(författare)
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A direct approach for three-dimensional elasto-static and elasto-dynamic solutions in curvilinear cylindrical coordinates with application to classical cylinder problems
- 2022
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Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 95
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with introducing a unique representation of the three-dimensional Navier's equations of motion in cylindrical coordinate system in an exact simplified form without any approximation, aiming at facilitating solution procedure for different 3-D elasto-static and elasto-dynamic problems in the future. A novel form of the 3-D elasticity equations of motion including the body forces in cylindrical coordinate system is derived in an uncoupled form in terms of the longitudinal (axial) displacement component and the 'r-theta' in-plane anti-symmetric rotation function instead of introducing any additional auxiliary unknown potential function. The other displacement components (i.e., circumferential and radial displacement components) are shown to be obtained from two independent equations in terms of the determined axial displacement and the aforementioned rotation component. The correctness, validity and easy implementation of the introduced elasticity approach for obtaining exact elasticity solutions for various 3-D elasto-static and elasto-dynamic problems are demonstrated through solving a number of known elasticity problems. Three-dimensional static and free vibrations of finitelength solid cylinders as well as thick-walled hollow cylindrical shells are analytically solved. Numerical comparative results and discussion are conducted. Excellent agreement between the obtained results and those reported in the literature is observed in all cases, confirming the validity of the proposed new approach.
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| 6. |
- Atashipour, Rasoul, 1983, et al.
(författare)
-
A realistic model for transverse shear stiffness prediction of composite corrugated-core sandwich elements
- 2017
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 129, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- Several previous studies of the transverse shear stiffness of corrugated-core sandwich elements have demonstrated that the existing analytical formulations significantly overestimate this property, especially when these lightweight elements are made of composite sub-elements. Due to the recent widespread fabrication and use of composite sandwich elements in many fields of application, a more accurate and reliable formulation is needed. This paper deals with an accurate analytical model for predicting the transverse shear stiffness of composite sandwich elements with a structural corrugated core. The effect of the directional material properties of the sub-elements, including face sheets and core, as well as the effect of a low shear modulus in composite material constituents of the sub-elements, is taken into ac- count. It is shown that the transverse shear stiffness of corrugated web core elements is considerably lower than that predicted by the existing formulations. The present solution provides much more real- istic results, especially when the corrugated-core sandwich is made of composite constituents with low shear moduli. Different combinations of the main orthotropic material orientation of the faces and core are studied comparatively for different composite material choices corresponding to an innovative timber composite floor case. It is demonstrated that the planar direction of the main orthotropic material ori- entation of the core has a significant influence on transverse shear stiffness, whereas that of the faces is less important. Several finite element comparisons are made to ensure the reliability of the developed for- mulation. The importance of the disregarded shear deformation effects on the transverse shear stiffness component versus different geometrical parameters of the sandwich element is studied and discussed.
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| 7. |
- Atashipour, Rasoul, 1983, et al.
(författare)
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A weak shear web model for deflection analysis of deep composite box-type beams
- 2018
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 155, s. 36-49
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Tidskriftsartikel (refereegranskat)abstract
- Deep box-type beams, consisting of framing members and sheathings, are sensitive to shear deformations andhence appropriate refined theories or complicated magnification factors are needed to be used to obtain accurate results. For sheathings or webs between the framing members that are weak in shear, additional shear deformations occur corresponding to the relative axial displacement between the framing members. These sandwich-type or partial interaction-type of in-plane shear behaviour between the framing members, needs to betaken into account, especially when the web shear stiffness is very low. The composite box-type beam treatedhere is composed of three framing members with sheathings on both sides. To incorporate effects of the sheathings shear deformations between the framing members on the deflection, the sheathings, here called web interlayers, are modelled as shear media with equivalent slip moduli corresponding to a partially interacting composite beam model. Governing equilibrium equations of the model are obtained using the minimum total potential energy principle and solved explicitly. The obtained results are compared with those based on different conventional beam theories and 3-D finite element (FE) simulations. It is shown that the model is capable of predicting accurately the deflection for a wide range of geometry and property parameters. It is demonstrated that the deflection of such deep box-type beams can be expressed as the summation of three different effects, namely bending deformations, conventional shear deformations in the framing members and sheathings, and additional in-plane shear deformations or shear slips of the weak web causing relative axial displacements between the framing members.
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| 8. |
- Atashipour, Rasoul, 1983, et al.
(författare)
-
Accuracy evaluation of gamma-method for deflection prediction of partial composite beams
- 2018
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Ingår i: WCTE 2018 - World Conference on Timber Engineering.
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Konferensbidrag (refereegranskat)abstract
- In this paper a precise model is established for deflection prediction of mechanically jointed beams with partial composite action. High accuracy of the proposed method is demonstrated through comparison with a comprehensive finite element (FE) modelling for a timber-concrete partial composite beam. Next, the obtained numerical results are compared with gamma-method, a well-known simplified solution for timber engineers according to the Eurocode 5. Validity and accuracy level of the gamma-method are investigated for various boundary conditions as well as different values of beam length-to-depth ratio, and discussed in details.
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| 9. |
- Atashipour, Rasoul, 1983
(författare)
-
An Elasticity solution for static analysis of functionally graded curved beam subjected to a shear force
- 2009
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Ingår i: International Journal of Engineering, Transactions B: Applications. - 1735-9244 .- 1728-144X. ; 23:2, s. 169-178
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Tidskriftsartikel (refereegranskat)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 all stress 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. |
- Atashipour, Rasoul, 1983
(författare)
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Exact elasticity solutions for thick-walled fg spherical pressure vessels with linearly and exponentially varying properties
- 2009
-
Ingår i: International Journal of Engineering, Transactions B: Applications. - 1735-9244 .- 1728-144X. ; 22:4, s. 405-416
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, exact closed-form solutions for displacement and stress components of thick-walled functionally graded (FG) spherical pressure vessels are presented. To this aim, linear variation of properties, as an important case of the known power-law function model is used to describe the FG material distribution in thickness direction. Unlike the pervious studies, the vessels can have arbitrary inner to outer stiffness ratio without changing the function variation of FGM. After that, a closed-form solution is presented for displacement and stress components based on exponential model for variation of properties in radial direction. The accuracy of the present analyses is verified with known results. Finally, the effects of non-homogeneity and different values of inner to outer stiffness ratios on the displacement and stress distribution are discussed in detail. It can be seen that for FG vessels subjected to internal pressure, the variation of radial stress in radial direction becomes linear as the inner stiffness becomes five times higher than outer one. When the inner stiffness is half of the outer one, the distribution of the circumferential stress becomes uniform. For the case in which the external pressure is applied, as the inner to outer shear modulus becomes lower than 1/5, the value of the maximum radial stress is higher than external pressure.
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