Impact response of thin-walled frame structures

This paper describes a finite-element method which was developed to predict the impact response of three-dimensional thin-walled frame structures.The softening effect of the load-deformation characteristics for thin-walled beams under combined axial compression, bending and torsional loads during impact is simulated by making use of a nonlinear Maxwell model.The large deformation of a structure is calculated by using updated nodal coordinates and internal forces, and the flexibility matrix for a curved beam element.Crash tests against a flat barrier were made on three-dimensional frame models. Comparisons between the calculated and experimental force-time relations and the deformed shape of the frame are discussed.     

Impact force location in frame structures

This paper describes a method to determine the location of an impact force using dynamic response measurements. The solution procedure combines frequency-domain problem solving methods using the spectral element method with a stochastic iterative search technique based on a genetic algorithm. Experimentally measured acceleration responses from two frame structures are used to verify the method.     

Instantaneous response of elastic thin-walled structures to rapid heating

A generalized modelling and analysis approach of thermally induced coupled vibrations of elastic thin-walled configurations with arbitrary open cross-sections are presented in conjunction with a unified implicit transient methodology. Limited research which takes into account the influence of rapid thermal heating effects on structures involving various forms of coupling appears in the literature. As a consequence, the dynamic response of such thin-walled structures of arbitrary open cross-section to rapid heating are described here. Effects involving triple, double, and no coupling between bending and torsional vibrations caused by sudden heating on these structures are examined. Numerical test cases are presented which describe the influence of sudden heating on elastic thin-walled structures of arbitrary open cross-sections.     

Impact strength of thin-walled composite structures under combined bending and torsion

The effect of bending and torsional stresses on the fracture characteristics of thin-walled square, rectangular and circular cylindrical structures has been investigated under static and impact loadings by use of the apparatus capable of applying bending and torsional moments in various proportions. The thin-walled structures were fabricated from glass-fiber strand, chopped strand mat and unsaturated polyester resin. Comparisons between experimentally determined strength and theoretical predictions using the failure criteria are presented. As a result of this investigation, the existence of the relation between the fracture mode and the strength was recognized and the failure criteria examined could be used successfully to predict the combined impact bending and torsional strength of thin-walled composite structures.     

Numerical investigation of structural crash response of thin-walled structures on soft soil

Accident statistics show that although the certification of aircraft structures is based on crash scenarios on hard or rigid surfaces, in reality most of the crash cases occur on soft soil or water. Therefore a structure which is designed for hard surfaces may not be safe enough for a possible crash scenario on water or soft soil. Finite element method (FEM) has been used in several numerical investigations and promising results were obtained. However, since soil is a granular medium this work aims at numerical modeling of the experimentally observed soil behavior using particle-based numerical technique. In this work numerical simulations of the crash tests on idealized cones and hemispheres were used to validate the models and compare FEM-based models with particle-based models. The results of numerical simulations were compared with quasi-static and dynamic test results conducted on coarse sand sample at the Deutsches Zentrum fur Luft- und Raumfahrt e.V (DLR). After obtaining a stable and accurate particle-based numerical model for the soft soil the crash performance of deformable metallic energy absorbers on soft soil ground was investigated and compared with test data and numerical investigations of rigid ground impacts.     

Magnetoacoustic diagnostics of thin-walled ferromagnets with plane cracks

We propose a new nondestructive method for the magnetic diagnostics of ferromagnetic thin-walled structures based on the analysis of acoustic-emission signals. The distribution of the magnetic field induced in a ferromagnetic half space by a magnetic dipole located over the surface of this half space is determined. The diagrams of dependence of the stress intensity factor on the location of a disk-shaped crack in the material are constructed.     

Load-carrying capacity of thin-walled composite structures

In the paper some basic ideas in approach to stability, post buckling behaviour and load carrying capacity of thin-walled composite structures are presented. Authors do not present equations that could only make the understanding of this issue “harder”.

Thin walled composite beam-coloumns with open and closed cross-section (channel and square cross-section) are calculated as an example. In order to analyse the stability and the structure performance after its loss, the ANSYS 5.7 package and authors' software has been used. Results obtained from both applied methods are compared. Presented examples show that the sole application of the FEM does not guarantee to obtain correct results of load carrying capacity and postbuckling path.     

Generalized mixed finite element model for pre- and post-quasistatic buckling response of thin-walled framed structures

Adopting an updated Lagrangian approach, the general framework for the fully non-linear analysis of thin-walled framed structures is developed using a simple, two-node, C⁰-model (HMB2). The governing equations are derived based on a consistent linearization of an incremental mixed variational principle of modified Hellinger/Reissner type with independent assumptions for displacement and strain fields. All coupled significant modes of deformations, i.e. stretching, bending, shear, torsion and warping, are accounted for in the generalized-beam theory employed. Emphasis is placed on devising effective solution procedures to deal with finite rotations in space, particularly with regard to their effect on the derivations of load-correction matrices corresponding to configuration-dependent externally applied forces/moments. The effectiveness and practical usefulness of present model are demonstrated through a number of test problems involving beam assemblages undergoing large displacements and rotations in space.     

Local surface nanocrystallization for buckling-resistant thin-walled structures

International Journal of Mechanics and Materials in Design - An innovative and new technology on enhancing buckling resistance is established in this work by making use of local surface...     

Non-linear analysis of thin-walled structures using plate elements

This paper presents a simple and efficient rectangular thin plate element for elastic geometric non-linear analysis of thin-walled structures. Based on the updated Lagrangian formulation and small strain hypothesis, this element can accurately predict the non-linear pre- and post-buckling load–deflection paths of a plate structure. Using symbolic manipulation, the linear and geometric stiffness matrices for the rectangular thin plate element are derived explicitly, thereby eliminating the need for numerical integration. The element contains 30 degrees of freedom (d.o.f.): 14 d.o.f. for the in-plane (membrane) action and 16 d.o.f, for the out-of-plane (bending) action. Several examples involving the large deflection behaviour of thin-walled structures are presented to demonstrate the accuracy, efficiency and versatility of the method.     

Buckling of thin-walled composite structures with intermediate stiffeners

The interactive buckling of prismatic, thin-walled composite columns with open sections, reinforced with intermediate stiffeners and with edge reinforcements, has been considered. The columns are assumed to be simply supported. The nonlinear problem has been solved with the Koiter’s asymptotic theory within the first order approximation. The asymptotic theory of the first order nonlinear approximation allows for simultaneous evaluation of the effect of imperfections and interactions of various modes of buckling on the behaviour of thin-walled structures. This evaluation can be only the lower bound estimation of the load carrying capacity. Detailed calculations have been made for several cases of columns.     

Thermoelastic sloping thin-walled shell structures deformed without bending

We have derived a nonlinear integrodifferential equation to find the unbent shape of the middle surface of a sloping shell of constant thickness, subjected to a given temperature and force field.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 2, pp. 314–316, August, 1990.     

Numerical simulation of brittle fracture of thin-walled structures1

The model of brittle material, allowing for the determination of initiation and growth of cracks in thin-walled structures up to their destruction, is offered. Solutions of some problems are submitted: destruction of a plate at a homogeneous stress state; destruction of a beam at a pure bending; dynamic deformation and destruction of a plate with the concentrated mass having various initial speeds. Destruction of part of the material of the plate is shown to result in dynamic loss of stability of the solution.     

Determination of the strained state of thin-walled cellular structures

By using Fourier series, we find the components of the vector of displacements of the middle surface of cellular cylindrical shells and compare the results with the corresponding averaged components. This enables us to justify the possibility of application of the averaged method to the analyses of the strained states of cellular pipelines on the engineering level. Two boundaryvalue problems of finding deflections in structures of this sort are solved.     

Impact damage response of natural stitched single lap-joint in composite structures

In this paper the damage behaviour of natural stitched composite single lap-joints are investigated under low velocity impact loading conditions. For this study, the laminated hybrid composite beams were pinned using Flax yarns before curing process. The Charpy impact test was chosen to study the energy absorbing capability of single lap composite joints. Composite beams were fabricated from combination of glass/epoxy and carbon/epoxy composites. It was shown that composite beams which are stitched through the thickness are able to absorb more energy in comparison with adhesive bonded composite joints in the hybrid composite beams. The Charpy impact test of stitched composite single lap joint was also simulated by finite element analysis using software LS-DYNA and the results verified with relevant experimental data.     

Application of manufacturing constraints to structural optimization of thin-walled structures

Topology optimization can be a very useful tool for creating conceptual designs for vehicles. Structures suggested by topology optimization often turn out to be difficult to implement in manufacturing processes. Presently, rail vehicle structures are made by welding sheet metal parts. This leads to many complications and increased weight of the vehicle. This article presents a new design concept for modern rail vehicle structures made of standardized, thin-walled, closed, steel profiles that fulfil the stress and manufacturing requirements. For this purpose, standard software for topology optimization was used with a new way of preprocessing the design space. The design methodology is illustrated by an example of the topology optimization of a freight railcar. It is shown that the methodology turns out to be a useful tool for obtaining optimal structure design that fulfils the assumed manufacturing constraints.     

大跨连续刚构桥双肢薄壁墩抗震性能研究

为获得双肢薄壁墩在地震作用下的破坏形态与力学性能,采用低周反复荷载试验探讨了不同轴压比、主筋率及体积配箍率对该类型桥墩抗震性能的影响,得到了各试验墩的破坏特性、滞回曲线、位移延性与耗能性能。试验结果表明:各试验墩的破坏形态基本相似,大体可分为三个阶段:弹性阶段、弹塑性阶段、弯曲破坏阶段。试验墩在墩底及系梁处破坏严重,其中墩底与墩顶出现显著的弯曲破坏,系梁处出现“X形”裂缝。主筋率较高的双肢薄壁墩滞回曲线较为饱满,耗能性能良好,适当提高轴压比可显著提高该桥墩的延性性能。各试验墩的变形能力较好,位移延性在2.63~3.68,变化幅度较大,主筋率对延性影响显著。     

Dynamic stability of cracked multi-bay frame structures

The effects of crack depth and crack location on the in-plane static and dynamic stability of cracked multi-bay frame structures subjected to periodic loading have been investigated numerically by using the finite element method. For the rectangular cross-section beam, a crack element is developed by using the principles of fracture mechanics. In addition, the effect of the number of spans and static and dynamic load parameters on static and dynamic stability analysis are also investigated. For buckling and dynamic stability analyses, the results obtained by using the present model are presented in three-dimensional graphical forms and tables.     

Local buckling of thin-walled structures by the boundary element method

In this work a multi-region boundary element formulation for linear local buckling analysis of assembled plate and shallow shell structures is presented. The assembly is divided into sub-regions. In each sub-region, the formulation is formed by coupling boundary element formulations of shear deformable plate bending and two-dimensional plane stress elasticity. Domain integrals appearing in the formulation (due to the curvature and due to the domain load) are transformed into equivalent boundary integrals. Membrane stresses at discrete domain points of each sub-region (plate or shallow shell) in the assembly are obtained from the prebuckling state, resulting in a set of linear buckling equations in terms of the buckling deflection and the buckling load factor. Buckling equation is presented as a standard eigenvalue problem. Results are compared with FEM solutions and it is shown that good accuracy can be achieved with the present multi-region BEM formulation.