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Abstract: Starting from the micro-structural definition of the stress tensor, Rothenburg and Bathurst (1989) derived a stress–force–fabric relationship for granular materials by approximating the directional distributions of the fabric, more specifically, the contact normal density distribution in this paper and the contact forces with Fourier functions and integrating over directions. This paper aims to assess the validity of the two key assumptions made during their derivation using particle-based numerical simulation in the cases of proportional loading and non-proportional loading. These two assumptions are (i) the 2nd-rank Fourier functions adopted are good enough to approximate the directional distributions of contact normal densities and contact forces and (ii) the principal directions of contact forces and contact normal density are coaxial. Numerical simulations have been carried out to conduct virtual experiments on the behaviour of isotropic specimens to monotonic loading, of isotropic specimens to stress rotation, and of anisotropic specimens to monotonic loading. The first one stands for the case of proportional loading while the latter two are non-proportional loading paths involving rotation of the frame of principal stresses and the frame of fabric, respectively. The directional distributions of contact normal density and contact forces are traced during these three typical loading processes. The simulation results indicate that the 2nd-rank Fourier functions give reasonable approximations, while the coaxial assumption is generally not valid in non-proportional loading. In the case that the principal directions of contact normal density and contact force differ, a more general expression of the stress–force–fabric relationship is required. This research can help to improve our understanding of the stress state and hence shear strength of granular materials based on the particle scale investigation. [Copyright &y& Elsevier]

Abstract: In stochastic finite element problems the solution of a system of coupled linear random algebraic equations is needed. This problem in turn requires the calculation of the inverse of a random matrix. Over the past four decades several approximate analytical methods and simulation methods have been proposed for the solution of this problem in the context of probabilistic structural mechanics. In this paper we present a new solution method for stochastic linear equations. The proposed method is based on Neumann expansion and the recently developed joint diagonalisation solution strategy. Unlike the classical Neumann expansion, here only the inversion of a diagonal matrix is needed. Numerical examples are given to illustrate the use of the expressions derived in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional (3D) cyclic analysis and constitutive material model are needed to better understand the behavior of unreinforced masonry (URM) buildings under earthquake excitations. So far, most of the existing constitutive material models applied to the field of masonry structures have focused on two-dimensional modeling and monotonic loading. In addition, most of the studies have used implicit dynamic procedures in the time domain. Based on the inherent features of implicit formulations for nonlinear problems, a number of iterations are required at each time step to achieve convergence, which leads to intensive computations and lack of convergence in some cases such as cyclic loadings. In this paper, a 3D cyclic constitutive material model implemented within an explicit analysis procedure is proposed, which can be used to model large deformation behavior of masonry walls. A rigorous constitutive material model is proposed and validated with available experimental data from previous researches, and for the attributes for which experimental data is not readily available; a number of new experimental tests has been conducted by the authors. The material model is implemented in a user-defined subroutine and compiled with ABAQUS (VUMAT). The subroutine is then tested by several numerical examples on a single element under cyclic normal and transverse deformations to examine the behavior of the material model. Moreover, several analyses are conducted and the numerical results are compared with experimental data to assess the robustness and predictive capabilities of the proposed material model and the numerical solution algorithms. [Copyright &y& Elsevier]

Abstract: The crack band approach has been used in many engineering computations as a simple technique eliminating or reducing the sensitivity of numerical results to the size of finite elements in simulations that involve strain localization due to softening. In the present paper, this traditional technique is carefully analyzed and potential sources of errors are identified. The role of various components of the modeling strategy is elucidated by simple examples dealing with a one-dimensional tensile test and a two-dimensional model of a notched beam subjected to bending. The influence of the specific choice of finite elements, integration scheme and formula for estimation of the crack band width is analyzed. Particular attention is devoted to the differences among band width estimation methods based on element area or volume, on element projection, and on the idea proposed by Oliver . The results are summarized in the form of recommendations which can contribute to reduction of errors in practical simulations. [Copyright &y& Elsevier]

Abstract: Phenomenological models are employed into composite structural systems for simulating passive devices aimed at vibration mitigation and the Bouc-Wen one subsists as a significant example. In recent years, the control systems progress has moved toward a more efficient and adaptable semi-active technology. Therefore the existent numerical procedures, which proved effective for the passive implementation, are expected to comprise such features as well. This paper deals with a method of controlling in real time the hysteresis component in simulated semi-active control systems through the Bouc-Wen model. An introductive discussion on the theoretical formulation of the original settlement allows to focus on a way for tuning the parameters which can be managed for hysteresis regulation. Proper algorithms, embedded into the analytical formulation of the model, are subsequently selected for implementing the semi-active characteristic. Finally, straightforward dynamic applications on a plane oscillator system point out the general capability of the proposed approach by seismic response simulation and mitigation of the induced structural effects. [Copyright &y& Elsevier]

Abstract: This paper deals with simulating the mechanical response of fiber-reinforced cementitious composites (FRCCs) by means of a zero-thickness interface model formulated within the framework of discrete-crack approaches. Following a similar model already available in literature for plain concrete, the formulation of the interface element is further developed and extended to capture the key mechanical phenomena controlling the FRCC behavior. An original approach is introduced for reproducing the complex influence of fibers on the cracking phenomena of the concrete/mortar matrix. Numerical analyses demonstrate the capabilities of the proposed model and show a very good agreement with experimental results on FRCC tests. [Copyright &y& Elsevier]

Abstract: The world’s largest plasma fusion experimental device of the stellarator family named Wendelstein 7-X (W7-X) [http://www.ipp.mpg.de/ippcms/eng/for/projekte/w7x/index.html] is being built at the Max-Planck-Institute for Plasma Physics (IPP) in Greifswald, Germany. The mission of the experiment is to prove the fusion reactor relevance of the stellarator principle . Main subject of this paper is the description of the numerical simulation of the highly complex and multiple nonlinear W7-X magnet system structure with the code ADINA. This code was chosen right from the start of the project and has later been used in parallel with the subsequently installed ANSYS and ABAQUS codes until now. The ADINA W7-X global structure model is the result of a long term R&D work on the superconducting coils and related support structure optimization. Despite the fact that W7-X is already in the assembly phase, there are still large structural analysis efforts going on. Their aim is to accompany the machine construction by evaluating specific assembly issues, non-conformities and design changes, but also to evaluate the operational limits of the experimental device which in many respects is an absolute prototype worldwide. [Copyright &y& Elsevier]

Abstract: Electron beam welding is a highly efficient and precise welding method that is being increasingly used in industrial manufacturing and is of growing importance in industry. Compared to other welding processes it offers the advantage of very low heat input to the weld, resulting in low distortion in components. Modeling and simulation of the laser beam welding process has proven to be highly efficient for research, design development and production engineering. In comparison with experimental studies, a modeling study can give detailed information concerning the characteristics of weld pool and their relationship with the welding process parameters (welding speed, electron beam power, workpiece thickness, etc.) and can be used to reduce the costs of experiments. A simulation of the electron beam welding process enables estimation of weld pool geometry, transient temperature, stresses, residual stresses and distortion. However this simulation is not an easy task since it involves the interaction of thermal, mechanical and metallurgical phenomena. Understanding the heat process of welding is important for the analysis of welding structure, mechanics, microstructure and controlling weld quality. In this paper the results of numerical simulation of electron beam welding of tubes were presented. The tubes were made of 30HGSA steel. The numerical calculation takes into consideration thermomechanical coupling (TMC). The simulation aims at: analysis of the thermal field, which is generated in welding process, determination of the heat-affected zone and residual stresses in the joint. The obtained results allow for determination both the material properties, and stress and strain state in the joint. Furthermore, numerical simulation allows for optimization of the process parameters (welding speed, power of the heat source) and shape of the joint before welding. The numerical simulation of electron beam welding process was carried out with the ADINA System v. 8.6. using finite element method. [Copyright &y& Elsevier]

Abstract: Structural health monitoring (SHM) has the potential to provide quantitative and reliable data on the real condition of structures, observe the evolution of their behaviour and detect degradation. This paper presents two methodologies for model-free data interpretation to identify and localize anomalous behaviour in civil engineering structures. Two statistical methods based on (i) moving principal component analysis and (ii) robust regression analysis are demonstrated to be useful for damage detection during continuous static monitoring of civil structures. The methodologies are tested on numerically simulated elements with sensors for a range of noise in measurements. A comparative study with other statistical analyses demonstrates superior performance of these methods for damage detection. Approaches for accommodating outliers and missing data, which are commonly encountered in structural health monitoring for civil structures, are also proposed. To ensure that the methodologies are scalable for complex structures with many sensors, a clustering algorithm groups sensors that have strong correlations between their measurements. Methodologies are then validated on two full-scale structures. The results show the ability of the methodology to identify abrupt permanent changes in behavior. [Copyright &y& Elsevier]

Abstract: This paper describes a perturbation-based stochastic homogenization analysis method for a thermal expansion coefficient of a fiber reinforced composite material using the equivalent inclusion method. The proposed method is formulated for evaluation of the probabilistic characteristics of the homogenized thermal expansion coefficients considering uncertainties in material properties and geometry of a component material. As a numerical example, the probabilistic characteristics of the homogenized thermal expansion coefficients of a unidirectional fiber reinforced plastic are analyzed. With comparison between the results of the proposed method and the results of the Monte-Carlo simulation, validity, accuracy and effectiveness of the proposed method are investigated. [Copyright &y& Elsevier]

A moving rail vehicle may cause propagating waves to the surroundings potentially leading to detrimental effects for the track construction, nuisances for the surroundings and interference with delicate electronic equipment. A full computational model should be able to couple a correct simulation of the rigid body motion of the different train parts with accurate prediction of the solid wave propagation in the ground. This paper integrates the dynamics of the vehicle and the elastic soil into one monolithic system. Equations of motion for the train have been merged the system representing the FEM problem for the rest of the structure. Three models of modern high-speed locomotives were run over a solid finite element model of a rail structure. [Copyright &y& Elsevier]

Abstract: Mesoscale analysis is a promising discipline for concrete mix design and damage prediction. Besides many other aspects, its success crucially depends on accurate modeling of the mesoscale geometry and efficient numerical analysis of high resolution, to both of which this article contributes. Mesoscale models of concrete include aggregates, cement stone and, optionally, interfacial transition zones. The present paper establishes transparent formulas for consistent numerical generation of aggregate sizes. Fast separation checks are applied to place ellipsoidal and in particular arbitrary shaped particles. The multigrid method enables efficient computation of very large heterogeneous mesoscale models. This is exemplified by linear finite element analysis of two-dimensional models. Corresponding results are confirmed by experiments and analytical models from literature. The influence of concrete mix parameters on effective elastic properties is studied. [Copyright &y& Elsevier]

Abstract: The present paper addresses the analysis of large-scale three dimensional magneto-mechanical problems by means of a coupled boundary element–finite element procedure. Iterative techniques are used for the solution of the associated linear systems; their intrinsic ill-conditioning is cured by means of ad-hoc multigrid solvers and fast multipole techniques as accelerators. Some numerical examples are presented in order to test the performance of the proposed approach. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to gain insight into finite element discretizations of shells using the basic shell mathematical model and, in particular, regarding the sources of “locking”. We briefly review the “basic shell mathematical model” and present a formulation of shell finite elements based on this model. These shell finite elements are equivalent to the widely-used continuum mechanics based shell finite elements. We consider a free hyperboloid shell problem, which is known to be difficult to solve accurately. Using a fine mesh of MITC9 elements based on the basic shell mathematical model, a detailed analysis is performed giving the distributions of all strain terms. A similar analysis using the MITC6 shell element shows why this element locks when the shell thickness is very small. [Copyright &y& Elsevier]