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The variational principles and corresponding finite element formulations are developed in this work for the free vibration and buckling analysis of partial-interaction composite beams under complex engineering situations, such as axial loading conditions, non-uniform material distributions, multi-span boundaries. The composites structures consist of sub-components connected with shear connections of finite rigidities and thus suffer from the partial-interaction phenomenon, significantly affecting the structural performance. The macroscopic elements for dynamic and buckling behavior are explicitly derived by simultaneously considering the sub-elements' deformations and interlayer slips, avoiding the stress concentrations in the contact areas existing in the commercial packages. The generated frequencies and critical loads of several orders for the single- or two-span composite structures with different boundary conditions are then validated against the analytical and numerical results in the literature with well-matched agreement. The interfacial shear connections and structural parameters are also studied of their influences on the structural dynamic and buckling behavior. The present theory is finally implemented in the theoretical analysis of the steel box-girder viaduct with non-uniformly-distributed shear braces and multi-span continuous composite beams of Jiubao Bridge. The explicit expressions of the elements are provided and can be readily implemented into the commercial software with high computational efficiency. [ABSTRACT FROM AUTHOR]

This study presents the numerical analyses conducted to investigate the impact behavior of different porous concretes, which have also been cast and tested experimentally. For a realistic representation of the real porous concretes containing arbitrary shaped air pores, a mesh generation code was developed in which the aggregates in the mixtures were directly extracted through computed tomography. In the code, mineralogically different aggregates in porous concretes with gravel could also be individually defined. In the explicit finite element analyses conducted, porous concrete was considered as a four-phase material, consisting of aggregates, interfacial transition zones (ITZ), bulk cement paste and air. The pore size distribution and the fragmentation behavior of the concretes were also numerically analyzed. Among the parameters that have been investigated both numerically and experimentally, aggregate grading, which determines the porosity and pore size distribution of the material, was found to have a dominant effect on the strength as well as the fragmentation properties of porous concretes. Although the amount of ITZ is higher in mixtures containing finer aggregates, those mixtures had higher impact strengths compared to coarser aggregate ones again owing to their much finer pore structures. [ABSTRACT FROM AUTHOR]

As traffic density and axle loads increase, the macroscopic wheel-rail contact can lead to severe rail wear. This paper constructs a multi-scale analysis framework from macroscopic force characteristics to microscopic wear mechanisms based on explicit finite element methods and molecular dynamics models. The study shows that the mutual proximity and annihilation of reverse dislocations in the rail material under the action of wheel-rail forces is an important cause of grain boundary fragmentation, while the proliferation of dislocations on the Subsurface leads to work hardening of the rail. The analytical framework proposed in this paper achieves a multiscale correlation between wheel-rail macroscopic contact and material microscopic response, and the conclusions obtained reveal the microscopic wear mechanism of rail materials. [ABSTRACT FROM AUTHOR]

Abstract: The intention of this paper is to give a comparative review of material models for polymers with special focus on crashworthiness analysis. An outline of polymers classified as incompressible elastomers, compressible foams and thermoplastics is shown. Elastomers and recoverable foams are based on the same theoretical description: hyperelasticity. We present a material law that allows fast generation of input data based on uniaxial static and dynamic tensile tests at different strain rates. For thermoplastics, we give a short overview of suitable material laws and show how we can characterize approximately their behaviour by using metal plasticity. Using pedestrian protection as an example, we demonstrate some typical applications of polymer modelling in crash simulation. Furthermore, we investigate the deformation behaviour of a Hardy disk during a frontal offset impact. [Copyright &y& Elsevier]

Expressions for critical timesteps are provided for an explicit finite element method for plane elastodynamic problems in isotropic, linear elastic solids. Both 4-node and 8-node quadrilateral elements are considered. The method involves solving for the eigenvalues directly from the eigenvalue problem at the element level. The characteristic polynomial is of order 8 for 4-node elements and 16 for 8-node elements. Due to the complexity of these equations, direct solution of these polynomials had not been attempted previously. The commonly used critical time-step estimates in the literature were obtained by reducing the characteristic equation for 4-node elements to a second-order equation involving only the normal strain modes of deformation. Furthermore, the results appear to be valid only for lumped-mass 4-node elements. In this paper, the characteristic equations are solved directly for the eigenvalues using Mathematica and critical time-step estimates are provided for both lumped and consistent mass matrix formulations. For lumped-mass method, both full and reduced integration are considered. In each case, the natural modes of deformation are obtained and it is shown that when Poisson's ratio is below a certain transition value, either shear-mode or hourglass mode of deformation dominates depending on the formulation. And when Poisson's ratio is above the transition value, in all the cases, the uniform normal strain mode dominates. Consequently, depending on Poisson's ratio the critical time-step also assumes two different expressions. The approach used in this work also has a definite pedagogical merit as the same approach is used in obtaining time-step estimates for simpler problems such as rod and beam elements. [ABSTRACT FROM AUTHOR]