Papers by Keyword: Buckling

Abstract: A thorough analysis of slender columns under axial force and bending moment requires second order effects assessment. Concrete’s creep is one of the factors that increase lateral displacements of the bar in the long run. This phenomenon propitiates the instability and reduces its bearing capacity. This paper shows a procedure for assessing rheological effects based on Eurocode 2 method. This procedure will be added to structural analysis software which takes into consideration geometrical and mechanical non-linearity. As an example interaction diagrams for concrete-encased composite columns with different slenderness values are obtained. These diagrams will demonstrate that rheological effects have a greater influence as axial force eccentricity and slenderness values increase.

Abstract: Buckling restrained braces (brb), as a new kind of component for shock absorption, improved the ordinary support shortcoming of easy bearing flexure,when the earthquake take place, it has very good consumeing energy ability and ductility. In recent years, it has been used widely in the USA、Japan and Taiwan ,This article introduces classification of brb briefly as well as the influence of mechanics property and arranging position and so on to resist earthquake.

Abstract: Acceptable variations in the length of the valve stem, in a conventionally manufactured valve, give room to the possibility of the stem to buckle and get jammed in the guide. Salvaging such a situation is expensive and time consuming. The present paper addresses this problem by increasing the compliance of the valve stem by introducing holes in it. The desired elastic deformation along the length, however, causes transverse deformation, which needs to be minimized. The use of multiple holes helps achieve this. Taguchi Method based Design of Experiments using L25 orthogonal array has been used for performing the parametric design to arrive at the best settings of the 5 parameters. The optimal settings eliminate the buckling and thus make the operation of the valve stem robust against manufacturing variabilities.

Abstract: Using the geometric non-linear theory (The Total Lagrange Description) in dynamics we can establish the problem of the natural vibration of the structure including the effects of the structural and geometrical imperfections. The incremental stiffness matrix can take into account the residual stresses (structural imperfections) and the geometrical initial displacements (geometrical imperfections) as well. The behaviour of columns, frames and thin-walled structures is sensitive to imperfections. This theory and results can be used as a base for the non-destructive method for the evaluation of the level of the load and the imperfections.

Abstract: The paper carried out the buckling optimization on composite beam with hat stiffener by taking ply angle as optimal variables and the critical buckling load (CBL) as the optimal objective. Firstly, the paper established the mathematical optimization model, and then carried out sensitivity analysis of ply angle through Optimal Latin Hypercube Design, finally optimized the design of the layer using Genetic Algorithm. The results show that the CBL of stiffened beam with the optimized ply angle is increased by 64% than that with initial ply angle; CBL can be increased by changing the ply angle, the sheet should adopt the 0° or 90° layer, while the surface and center of stiffener should adopt ±45° layer and the rest should be 0° or 90°.

Abstract: The use of sandwich structures in various engineering fields is growing rapidly because of advantageous features such as low weight and high strength-to-weight ratio.The existing theories are all based on soft core assumption. In this case, the in-plane stress and the stiffness of the core are not included. It has been shown that Ressiner theory is inadequate for the analysis of hard-core sandwich plates. Different revision factors were put forward in this paper to revise the bending, buckling and free vibration results of soft-core Reissner theory for hard-core sandwich plates. The results show that the revised results go well with the hard core theory, so that its validity is confirmed.

Abstract: A finite element model with detailed anatomical structure of human cervical spine was established in this paper based on the CT scan data of the cervical vertebrae obtained from a 50th percentile Chinese male. The model was validated by the data from the head-neck drop test conducted by Nightingale et al in 1996. In the drop test simulation, the contact force between the head and impact surface, as well as head acceleration were chosen to gauge the accuracy of the model predictions against test results. The results show that the head - neck finite element model without muscle tissue has a consistent mechanics and dynamics with the body drop test. The model can be applied to the exploration of a more detailed neck injury model with muscle tissue and can also be directly applied to the study of injury mechanism of the cervical spine in the car crash accidents.

Abstract: During the manufacturing of fabric-reinforced composite parts using a matched-die compression molding process or liquid composite molding, the fabric may experience local in-plane compressive loads that cause out-of-plane deformations. The waves that result from this outofplane motion can lead to the formation of resin rich pockets (during the infusion stage of a dry fabric) or they may be forced down into a fold by the tooling. Defects such as resin-rich pockets and folds compromise the structural integrity of the formed composite part. Therefore, it is valuable to have a simulation tool that can accurately capture the fabric bending properties and predict the locations where waves or folds are likely to occur as a result of the manufacturing process. The tool can then be used to investigate changes in the forming parameters such that the development of such defects can be mitigated. A hybrid finite element model used with a discrete mesoscopic approach captures the behavior of continuous fiber-reinforced fabrics where the fabric yarn is represented by beam elements and the shear behavior is implemented in shell elements. User-defined material subroutines describe the mechanical behavior of the beams and shells for their respective contributions to the overall fabric behavior. Simulations are used to demonstrate the ability of the modeling approach to predict the amplitude and curvature of out-of-plane waves. The simulation results are compared with experimental data to show the accuracy of the modeling. Additional models are presented to demonstrate the capability of the simulation tool to capture fabric folding.

Abstract: Rolling of thin sheets generally induces flatness defects due to thermo-elastic deformation of rolls. This leads to heterogeneous plastic deformations throughout the strip width and then to out of plane displacements to relax residual stresses. In this work we present a new numerical technique to model the buckling phenomena under residual stresses induced by rolling process. This technique consists in coupling two finite element models: the first one consists in a three dimensional model based on 8-node tri-linear hexahedron which is used to model the three dimensional behaviour of the sheet in the roll bite; we introduce in this model, residual stresses from a full simulation of rolling (a plane-strain elastoplastic finite element model) or from an analytical profile. The second model is based on a shell formulation well adapted to large displacements and rotations; it will be used to compute buckling of the strip out of the roll bite. We propose to couple these two models by using Arlequin method. The originality of the proposed algorithm is that in the context of Arlequin method, the coupling area varies during the rolling process. Furthermore we use the asymptotic numerical method (ANM) to perform the buckling computations taking into account geometrical nonlinearities in the shell model. This technique allows one to solve nonlinear problems using high order algorithms well adapted to problems in the presence of instabilities. The proposed algorithm is applied to some rolling cases where “edges-waves” and “center-waves” defects of the sheet are observed.

Abstract: The main objective of the present work is to investigate the effect of the residual stresses originated by the friction stir welding (FSW) process in the compressive strength of aluminium alloy plates. The finite element method (FEM) is used to simulate the welding process and calculate the distribution of the residual stresses. The model is validated using a residual stress map obtained by means of the contour method from a friction stir welded AA2024-24 plate. The results from the welding simulation were then used to numerically assess the influence of the residual stresses on the collapse load of the plate.