Linear Buckling Analysis Considering No-compression Property of Metal Grid Shells Stiffened by Tension Braces

In order to analyze the buckling behavior of lattice shells stiffened by cables or slender braces without pre-tension, it is necessary to consider the no-compression property of braces. This paper proposes an innovative method of linear buckling analysis that considers the no-compression property of braces. Moreover, in order to examine the proposed method's validity, its results are compared with the results from a nonlinear buckling analysis with geometrical nonlinearity and material nonlinearity to express the no-compression property of braces. The results show that the proposed method can well-predict the buckling behaviors of lattice shells stiffened by tension braces.

Nonlinear buckling behavior of hybrid composites with different notch types

In this study, the effect of change of notch type on non-linear buckling behavior in composite plates was investigated experimentally and numerically. The composite plate is produced by applying the vacuum infusion method using carbon and aramid hybrid woven fabric and epoxy. Primarily, in the composite plates, a circular hole in the middle, a U single edge notch and semicircle double edge notches are formed. The specimens were subjected to buckling tests, being placed on their two edges, while the others were free. Afterwards, the load displacement graphs of the plates under pressure load were obtained experimentally for the behavior before and after buckling. In the numerical study, non-linear buckling analysis was performed using the finite element method. As a result, experimental and numerical buckling behaviors were obtained in accordance with each other. Since the net cross section bearing the pressure load is equal for all notch types, an effective difference between the maximum damage loads has not been achieved. So, the variation of notch type does not change the load displacement behavior characteristics of the plates after buckling. However, due to the unsymmetrical geometry in U notched plates, an uneven change in horizontal displacements along the width of the plate was achieved. The maximum stress concentration formed around the notch increased after buckling with the increase of displacement in vertical direction.

Buckling Analysis of Torpedo’s Cylindrical Shell

Torpedo is a self-propelled weapon. It can be launched above or below the water surface. Torpedo’s different internal parts are housed in cylindrical, conical and spherical shell structures. Underwater applications require the minimization of the structural weight of shell structure for increased buckling strength, speed, and operating distance. To serve this purpose lightweight material such as Al-Cu alloy is preferred for the manufacturing of torpedo’s cylindrical shell. Here in the present investigation, unstiffened cylindrical shell structural member of the torpedo is considered for the evaluation of its linear buckling strength when the torpedo is subjected to hydro-static pressure under the sea water. Linear buckling analysis which is also called Eigen buckling analysis is done on unstiffened cylindrical shell geometry by using ANSYS R14.5 software. The values obtained for linear buckling strength from empirical equations mentioned in British Standards Institution, BS 5500 (now superseded by PD 5500) ‘Unfired Fusion Welded Pressure Vessels’ are validated with those results from ANSYS R14.5 and are observed to be closer to each other. The variation of the failure stress of an unstiffened cylindrical shell due to buckling for the variation of its thickness is also observed using both the empirical and simulation using ANSYS R14.5 approaches and are compared using the corresponding plots. And also, the critical buckling pressures of an unstiffened cylindrical shell with a constant thickness for the formation of different number of lobes for the simply supported boundary conditions are calculated by using empirical relations and this variation is observed using the corresponding plot. For these analyses numerical examples are considered.

ANÁLISE DA INTEGRIDADE E DA INSTABILIDADE DINÂMICA DE UM SISTEMA MECÂNICO SUJEITO A BIFURAÇÃO DO TIPO BUTTERFLY

Slender structural systems susceptible to unstable buckling generally losestability at lower load levels than the linear buckling load of the perfect structure. This is mainly due to the geometric imperfections present in real structures. The objective of this work is to determine the integrity measures, together with the stability of the post-critical solutions of a mechanical system subject to unstable symmetrical buckling, Burtterfly-type bifurcation, using a discrete degree of freedom model. Uncertainties in the order of 10% will be considered in its deterministic parameters, to obtain lower and reliable limits for the project. The proposed uncertainty in the spring stiffness parameters does not change the type of bifurcation and the value of the critical load, only the value of the minimum post-critical of the bifurcation diagrams. The results showed the erosion of the attraction basin and the decrease of the factors of integrity, local and global, for the trivial solutions with the increase of the static load, for the investigated bifurcation.

Impact of Geometrical Imperfections on Estimation of Buckling and Limit Loads in a Silo Segment Using the Vibration Correlation Technique

The paper examines effectiveness of the vibration correlation technique which allows determining the buckling or limit loads by means of measured natural frequencies of structures. A steel silo segment with a corrugated wall, stiffened with cold-formed channel section columns was analysed. The investigations included numerical analyses of: linear buckling, dynamic eigenvalue and geometrically static non-linear problems. Both perfect and imperfect geometries were considered. Initial geometrical imperfections included first and second buckling and vibration mode shapes with three amplitudes. The vibration correlation technique proved to be useful in estimating limit or buckling loads. It was very efficient in the case of small and medium imperfection magnitudes. The significant deviations between the predicted and calculated buckling and limit loads occurred when large imperfections were considered.