Papers by Keyword: Buckling

Abstract: Trees' consistent shape and robust structure can withstand massive loads, which has influenced numerous architects and design engineers. Tree shape support structures are considered one of the most suitable alternatives to long-span roof-truss systems. Limited research has been undertaken on the structural efficiency of the columns with geometric subdivisions. This study investigates the Y-shape tree column's failure mechanism and damage index under static and lateral load. The variables considered are the external moment, subdivision element angle (θ), and joint failure volume of material (V_dj), investigating buckling and yielding behaviour. SAP2000 and ABAQUS are used in numerical modelling. The results revealed that when sliced half into branches, a symmetric column (prone to local buckling) switches the failure behaviour from buckling/ yielding to joint failure. Furthermore, V_dj has been found more in branches than stems, which increases with branch inclination (96.72% for θ =75^o). Considering both static and lateral load simultaneously resulted in a slight reduction (less than 35 %) in total V_dj but made the areas with high-stress asymmetric, making the support structure unfunctional comparatively at lesser load. The sliced column behaved like a single beam/column element for pure lateral load. To brace tree-shaped structures, this study recommends using a triangular wedge by welding the erected branches together just above the joint with the stem, increasing the overall affected joint area and making it resilient by reducing the stress intensity. Yet numerous areas need more exploration, such as integrating nonlinear behaviour and using a multilayer multi-material system utilizing high-fidelity modelling approaches.

Abstract: The effect of part geometry on premature thin wall part failure in laser powder bed fusion (LPBF) is investigated using FEM simulation. Two FEM models are used to simulate the residual stress and buckling modes. Two experimental parts with different lengths are used for model validations. A LPBF FEM model evaluates the residual stress associated with the two experimental parts. A parametric buckling model is developed to determine the eigenvalues for 100 different part geometries including different part lengths (20-60 mm), widths (0.5-2 mm), and heights (10-50 mm). The results show that thin wall parts are more susceptible to buckling mode 1 when part length is small and to a combination of mode 1 and 3 when part length increases. In both cases the threshold stress for buckling is mostly sensitive to part thickness and height.

Abstract: The present work aims at studying the buckling behavior of lattice structures realized by additive manufacturing technology. To this purpose, carbon fiber reinforced thermoplastic filaments have been used to realize anisogrid structure at different geometric parameters by means of Fused Filament Fabrication technology. Eight configurations were realized varying the rib width and the rib thickness of the structures, and keeping constant the cell height value. Anisogrid structures were tested under compressive load in order to investigate the effect of geometric parameters on strength and specific strength exhibited by the structures. It has been shown that mechanical performances of lattice structures are highly affected by the geometric parameters of the anisogrids.

Abstract: A Group of three specimens from 1312 steel were subjected to a range of elevated temperatures (700, 800, 900) Celsius to demonstrate the hazard of fire on steel columns mechanical proprieties. The results show a dangerous increase in creep strain buckling after 60 minutes from the beginning of the test and after 67 minutes failed to occur. Mechanical tests for normal and elevated temperatures were made to compare the fire hazards, the results depict reduction by 29%, 46%, 55% for young modulus of elasticity for elevated steel specimens (700, 800, 900) °C. for yield strength the value decreased by (128.4, 169.6, 189) Mpa for specimens (700, 800, 900) °C respectively. The ultimate stress reduction by (64, 78, 83) % from the normal value. whenever higher temperatures go up the lower the ultimate strain falls dawn by (50, 60, 66) % to the original ultimate strain value 0.5. the 0.2 strain % is decreased from 0.0029 to 0.0027 for 700 °C and increased to 0.011, 0.015 for (800, 900) °C respectively.

Abstract: The effect of layer thickness on hardness and buckling behavior was investigated on Ni-Co-Cu/Cu multilayered films. The Ni-Co-Cu/Cu multilayered films were grown on annealed copper substrates by electrodeposition. We fabricated the multilayered films with various layer thicknesses ranging from 10 nm to 1000 nm. First, dependence of Vickers hardness on the Cu layer thickness was investigated. When the Ni-Co-Cu layer had the constant thickness of 75 nm and the Cu layer thickness was smaller than 75 nm, the hardness increased rapidly with decreasing Cu layer thickness. Subsequently, compressive tests were conducted on the multilayered films having the component layers ranging from100 nm to 1000 nm, where the hardness values did not change rapidly with layer thickness. The copper substrates coated with the multilayered films were compressed until 20% strain. From SEM surface observations after the compressive tests, formations of band-like structures having a certain thickness were recognized. Cross-sectional observation revealed that some band-like structures were formed as a result of local buckling of the multilayered film. The vertical thickness of the bank-like structures increased linearly with increasing component layer thickness.

Abstract: The present paper investigates the nonlocal buckling of Zigzag Triple-walled carbon nanotubes (TWCNTs) under axial compression with both chirality and small scale effects. Based on the nonlocal continuum theory and the Timoshenko beam model, the governing equations are derived and the critical buckling loads under axial compression are obtained. The TWCNTs are considered as three nanotube shells coupled through the van der Waals interaction between them. The results show that the critical buckling load can be overestimated by the local beam model if the small-scale effect is overlooked for long nanotubes. In addition, a significant dependence of the critical buckling loads on the chirality of zigzag carbon nanotube is confirmed, and these are then compared with: A single-walled carbon nanotubes (SWCNTs); and Double-walled carbon nanotubes (DWCNTs). These findings are important in mechanical design considerations and reinforcement of devices that use carbon nanotubes.

Abstract: A railway bridge over several decades will be degraded due to localized corrosion. As a result, the load capacity of the bridge decreases, especially under the live load caused by trains. This paper examines the residual load capacity of a bridge deteriorated by localized corrosion by using the multibody dynamics approach. This approach allows an accurate description of the interaction between trains and bridges. At the same time, it allows the formation of corrosion marks on each structural member of the bridge in a numerical model precisely based on actual measured data. In order to describe accurately the remaining load of the bridge under the moving load of the train, a dynamic testing and finite element modeling of a steel bridge are conducted and compared. At the same time, the results are also compared with the simulation results of the bridge model before being corroded. In addition, the paper also tests the reliability of the numerical model for assessments of similar bridges without actual measurement results that are costly and time-consuming.

Abstract: The different approaches were analyzed to investigate the buckling problems of structurally-anisotropic panels made from composite materials. Aircraft composite structure design in the field of production technology is the outlook research trend. New mathematical model relations for the buckling investigation of structurally-anisotropic panels comprising composite materials are presented in this study. The primary scientific novelty of this research is the further development of the theory of thin-walled elastic ribs related to the contact problem for the skin and the rib with an improved rib model. One considers the residual thermal stresses and the preliminary tension of the reinforcing fibers with respect to panel production technology. The mathematical model relations for the pre-critical stressed state investigation of structurally-anisotropic panels made of composite materials are presented. Furthermore, the mathematical model relations for the buckling problem investigation of structurally-anisotropic panels made of composite materials are presented in view of the pre-critical stressed state. The critical force definition of the general bending form of the thin-walled system buckling and the critical force definition of the many-waved torsion buckling are of the most interest in accordance with traditional design practices. In both cases, bending is integral with the plane stress state. Thus, the buckling problem results in the boundary value problem when solving for the eighth order partial derivative equation in the rectangular field. The schematization of the panel as structurally-anisotropic has been proposed as a design model when and the critical forces of total bending form of buckling are determined. For a many-waved torsion buckling study, one should use the generalized functions set. The solution is designed by a double trigonometric series and by unitary trigonometric series. A computer program package is developed using the MATLAB operating environment. The computer program package has been utilized for multi-criteria optimization of the design of structurally-anisotropic aircraft composite panels. The influence of the structure parameters on the level of critical buckling forces for bending and for torsion modes has been analyzed. The results of testing series are presented.

Abstract: The paper deals with the design and development of a new and progressive structural types of footbridges with an external tendon used as a main load bearing member. Main goals of the paper are checking the possibilities of using such structures for many different spatial arrangements and especially identifying the problematic aspects of the design. Using the results of research conducted in previous years, the procedure for finding the optimal shape of the cable was described in detail. For specific examples the process of cable shape optimizations is shown. In the next part the influence of various boundary conditions is discussed. The structures were also checked in terms of ULS and SLS limit states. Particular attention is paid to the buckling analysis of the struts and stress distribution in the deck part. The structures were modeled using FEM software Midas Civil. The models used for basic analysis consist of beam and truss elements. For precise analysis the shell models were used. Finally the dynamic behavior analysis was performed according to SÉTRA methodology. The results and outputs of the research should be used by designers who have to deal with similar structural types and they shall hopefully help to identify the most problematic features.

Abstract: In present paper, a novel two variable shear deformation beam theories are developed and applied to investigate the combined effects of nonlocal stress and strain gradient on the bending and buckling behaviors of nanobeams by using the nonlocal strain gradient theory. The advantage of this theory relies on its two-unknown displacement field as the Euler-Bernoulli beam theory, and it is capable of accurately capturing shear deformation effects, instead of three as in the well-known first shear deformation theory and higher-order shear deformation theory. A shear correction factor is, therefore, not needed. Equations of motion are obtained via Hamilton’s principle. Analytical solutions for the bending and buckling analysis are given for simply supported beams. Efficacy of the proposed model is shown through illustrative examples for bending buckling of nanobeams. The numerical results obtained are compared with those of other higher-order shear deformation beam theory. The results obtained are found to be accurate. Verification studies show that the proposed theory is not only accurate and simple in solving the bending and buckling behaviour of nanobeams, but also comparable with the other shear deformation theories which contain more number of unknowns