جستجوی مقالات مرتبط با کلیدواژه « Dynamic Buckling » در نشریات گروه « مکانیک »
تکرار جستجوی کلیدواژه « Dynamic Buckling » در نشریات گروه « فنی و مهندسی »-
The static and dynamic behavior of a horizontal cylindrical shell (as used to store fuels in tanks) is investigated in this work by means of computational modeling. Under a distributed pressure commonly used to model effects due to explosions, the geometrically nonlinear behavior is explored to identify bifurcation and limit points along the static equilibrium path, and the associated displacements. Critical load reductions due to imperfections are found in the order of 25%. The dynamic analysis is next presented to identify the possibility of reaching a quasi-bifurcation. It is found that the first peak in the transient response at which the displacement reaches the same value as in the limit static case occurs for a load which is about 3.5 times the static bifurcation load. The velocity is zero at this state and is identified as a quasi-bifurcation, at which the shell is expected to display a static instability. Imperfection-sensitivity of the quasi-bifurcation load is found to be of the same order as the static one. This is the first quasi-bifurcation study of a shell to identify dynamic buckling due to a nearby explosion.Keywords: Dynamic buckling, Explosions, Imperfection-sensitivity, Quasi-bifurcations, Shell structures}
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در این مقاله پاسخ غیرخطی تغییرمکان یک پانل استوانه ای ساندویچی تحت بارگذاری دینامیکی ضربانی با درنظر گرفتن قابلیت تغییرشکل هسته مورد مطالعه قرار گرفته است. با استفاده از تیوری مرتبه بالای ارایه شده برای هسته پانل های ساندویچی، معادلات حاکم بر حرکت بر مبنای نظریه ارتجاعی سه بعدی به کار گرفته شده است. همچنین رفتار کمانش دینامیکی ضربانی صفحات جانبی پانل با استفاده از معیار بادیانسکی- راس، بررسی شده است. برای لایه های داخلی و خارجی پانل مواد اورتوتروپیک و برای لایه میانی مواد همسانگرد ویسکوالاستیک از جنس فوم پلی وینیل کلراید در نظر گرفته شد. تاثیر پارامترهای مختلف مانند ابعاد پانل، ضخامت هسته و لایه های جانبی، مدت ضربان و بیشینه فشار وارد شده روی پاسخ دینامیکی غیرخطی و مقاومت کمانشی پانل ساندویچی مورد مطالعه قرار گرفت. نتایج به دست آمده در این مقاله با نتایج ارایه شده در مقالات دیگر و همچنین نتایج به دست آمده از حل المان محدود در نرم افزار Ansys برای پانل های سه لایه مقایسه شده و دقت خوبی مشاهده شده است. نشان داده شده است که با افزایش ضخامت پانل یا کاهش شعاع آن، مقاومت کمانش دینامیکی ضربانی افزایش می یابد.
کلید واژگان: کمانش دینامیکی, پانل ساندویچی استوانه ای, هسته انعطاف پذیر_ انفجار, پاسخ غیرخطی}In this paper, three-dimensional displacement response of a cylindrical sandwich panel with compressible core under the action of dynamic pulse loading is addressed using the extended high order sandwich panel theory. Also, local dynamic pulse buckling of facesheets is studied by considering the Budiansky-Roth buckling criterion. It is assumed that the sandwich panels consist of orthotropic face sheets and an isotropic viscoelastic foam core layer. The effects of various parameters including the panel span, core and facing thickness, pulse duration and maximum pressure on the non-linear dynamic response and buckling strength of the sandwich cylindrical panel are studied. The results obtained from the present method are compared with finite element solutions using the commercial software ANSYS and those reported in the literature, showing a good agreement. It is revealed that applied core non-linear theory could be satisfactory for the dynamic pulse response of sandwich viscoelastic panels. It is also shown that the pulse buckling strength of panel increases with a decrease of the panel radius or an increase of the panel thickness.
Keywords: Dynamic buckling, Cylindrical sandwich panel, Compressible core, Blast, Nonlinear response} -
In the present study, the dynamic buckling of the graphene sheet coupled by a viscoelastic matrix was studied. In light of the simplicity of Eringen's non-local continuum theory to considering the nanoscale influences, this theory was employed. Equations of motion and boundary conditions were obtained using Mindlin plate theory by taking nonlinear strains of von Kármán and Hamilton's principle into account. On the other hand, a viscoelastic matrix was modeled as a three-parameter foundation. Furthermore, the differential quadrature method was applied by which the critical load was obtained. Finally, since there was no research available for the dynamic buckling of a nanoplate, the static buckling was taken into consideration to compare the results and explain some significant and novel findings. One of these results showed that for greater values of the nanoscale parameter, the small scale had further influences on the dynamic buckling.Keywords: Dynamic buckling, Graphene sheet, Viscoelastic matrix, Differential quadrature method}
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Computations and Simulations in Mechanical Science, Volume:1 Issue: 1, Winter and Spring 2018, PP 1 -11In this paper, dynamic behavior of long metallic bars subjected to axial impact is investigated experimentally and numerically. Bars made of steel without and with attached mass are impacted against a rigid wall. Experimental tests are performed by gas gun and numerical results are obtained using FE simulation. Results of shortening, axial force and buckling shape of two mentioned bars are presented. Obtained results for bar without and with attached mass with the same impact energy are compared. It is found that at the same impact energy, shortening and axial force of empty bar and bar together with attached mass is identical, approximately. Also, the deformation mechanism of empty bar and bar together with attached mass is different in which the radial deflections of bar with attached mass is higher than bar without attached mass. Comparing experimental and numerical results shows a good agreement between them.Keywords: Long bars, Axial impact, Dynamic buckling, Gas gun, Deformation mechanism}
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In this study, the dynamic buckling of the embedded laminated nanocomposite plates is investigated. The plates are reinforced with the single-walled carbon nanotubes (SWCNTs), and the Mori-Tanaka model is applied to obtain the equivalent material properties of them. Based on the sinusoidal shear deformation theory (SSDT), the motion equations are derived using the energy method and Hamilton's principle. The Naviers method is used in conjunction with the Bolotin's method for obtaining the dynamic instability region (DIR) of the structure. The effects of different parameters such as the volume percentage of SWCNTs, the number and orientation angle of the layers, the elastic medium, and the geometrical parameters of the plates are shown on DIR of the structure. Results indicate that by increasing the volume percentage of SWCNTs the resonance frequency increases, and DIR shifts to right. Moreover, it is found that the present results are in good agreement with the previous researches.Keywords: Dynamic buckling, Nanocomposite laminated plates, elastic medium, SSDT, Bolotin method}
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The dynamic stability of a composite plate with external electrorheological (ER) damper subjected to an axial periodic load is investigated. Electrorheological fluids are a class of smart materials, which exhibit reversible changes in mechanical properties when subjected to an electric field. As a result, the dynamic behavior of the structure is changed. The ER damper is used for suppressing the vibrations and improving the stability of the system. The Bingham plastic model is employed to express the behavior of the ER fluid. The finite element model of the structure is developed and constant acceleration average method is used to obtain the response of the system. Effect of different parameters such as the electric field, the orientation of the ER damper, the initial gap between the two electrodes of the ER damper and the stacking sequences of the plate on the first instability boundaries of the composite plate are investigated.Keywords: Laminated composite, Dynamic buckling, FEA, Smart structures}
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In this paper, the nonlinear dynamic buckling of double-walled boron-nitride nanotube (DWBNNT) conveying viscous fluid is investigated based on Eringen''s theory. BNNT is modeled as an Euler-Bernoulli beam and is subjected to combine mechanical, electrical and thermal loading. The effect of viscosity on fluid-BNNT interaction is considered based on Navier-Stokes relation. The van der Waals (vdW) interaction between the inner and outer nanotubes is taken into account and the surrounding elastic medium is simulated as Winkler and Pasternak foundation. Considering the charge equation for coupling of mechanical and electrical fields, Hamilton''s principle is utilized to derive the motion equations based on the von Kármán theory. Dynamic buckling load is evaluated using differential quadrature method (DQM). Results show that dynamic buckling load depends on small scale factor, viscosity, elastic medium parameters and temperature changes. Also, dynamic instability region is discussed for various conditions.Keywords: Dynamic Buckling, DWBNNT, Viscous Flow, Pasternak Medium, DQM}
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