Mario Fafard

A general multi‐axle vehicle model to study the bridge‐vehicle interaction

Develops a general five‐axle vehicle model to study the dynamic interactions between the moving mass and the bridge structural components. Two‐axle, three‐axle, or four‐axle sprung loads, and the limiting load conditions such as a moving constant force, a moving alternating force, a moving unsprung mass, and combinations thereof, can be treated as special cases of the more general case presented. Further, its integration with the versatile finite element modelling has enhanced the practical applicability of such a theoretical development. The physical characteristics of the bridge and the vehicle, such as the bridge geometry, mechanical properties, profile of the road surface, the vehicle parameters including the distance between axles, leaf springs suspension and the total weight, are considered explicitly in the present model. The dynamic equations of equilibrium in time are integrated using the Newmark integration scheme. Verifies the accuracy of the algorithm by comparing the numerical results obtained from the present formulation with the experimental results.

Geometrical interpretation of the arc-length method

The arc-length method is a powerful solution technique becoming increasingly popular among researchers and engineers. This method is presented here as a particular case of a more general formulation which includes all other solution strategies. The arc-length method is derived in its continuous and discrete formulations. Two versions of the arc-length method (Crisfield and Ramm) are presented and compared using a geometrical interpretation. Advantages and disadvantages of each method are pointed out. A new method, called the modified Crisfield-Ramm method, is proposed. This improved arc-length method combines the advantages of the two parent methods.

A new discrete Kirchhoff plate/shell element with updated procedures

Abstract We present a new six-node triangular plate/shell clement (called DLTP) for geometrical and material nonlinear analysis. The formulation is based on small elasto-plastic strains and updated Lagrangian formulation (ULF). Two updated procedures are compared in the elastic and plastic range. The DLTP element is obtained by superposition of a discrete Kirchhoff model (DKTP) for bending and a linear strain triangular element for membrane (LST). Several numerical examples are presented employing special solution strategies for tracing the pre- and post-buckling curves.

Carbon to cast iron electrical contact resistance constitutive model for finite element analysis

Abstract The electrical contact resistance at the interface between two materials is often an unknown when modelling certain processes, such as the anodes and cathodes in Hall–Heroult cells or the spot welding of sheet metal. In this paper, a 2D axisymmetric weakly coupled thermo-electro-mechanical finite element methodology built in the commercial code ANSYS is presented. It allows the generation of Joule heat directly at the interface, the precise representation of the contact areas as well as the testing of different contact resistance models. Using existing experimental results of industrial carbon and steel cylinders in contact at different temperatures, a novel phenomenological constitutive law for electrical contact resistance was developed. This experiment was repeated at room temperature with Alcoa-Lauralco carbon and cast iron cylinders, and the 2D finite element model was used to validate and calibrate the constitutive law. An excellent agreement was found between the model predictions and the new experimental data.

Aluminum reduction cell anode stub hole design using weakly coupled thermo-electro-mechanical finite element models

Abstract Electrical power accounts for the largest part of the primary aluminum production cost, hence smelters strive to improve their overall efficiency. Current Hall–Heroult reduction cell technology generally uses cast iron to connect steel conductors to carbon electrodes. In this paper, the reduction of anodic connector electrical losses was investigated through a combination of simple experiments and weakly coupled thermo-electro-mechanical finite element models. A novel phenomenological constitutive model was used to predict the electrical contact resistance at the cast iron to carbon interface. Parametric design studies were carried, and substantial savings are expected from the optimization of the anodic connector geometry.

A global rheological model of wood cantilever as applied to wood drying

In the process of wood drying inevitable stresses are induced. This often leads to checking and undesired deformations that may greatly affect the quality of the dried product. The purpose of this study was to propose a new rheological model representation capable to predict the evolution of stresses and deformations in wood cantilever as applied to wood drying. The rheological model considers wood shrinkage, instantaneous stress–strain relationships, time induced creep, and mechano-sorptive creep. The constitutive law is based on an elasto–viscoplastic model that takes into account the moisture content gradient in wood, the effect of external load, and a threshold viscoplastic (permanent) strain which is dependent on stress level and time. The model was implemented into a numerical program that computes stresses and strains of wood cantilever under constant load for various moisture content conditions. The results indicate that linear and nonlinear creep behavior of wood cantilever under various load levels can be simulated using only one Kelvin element model in combination with a threshold-type viscoplastic element. The proposed rheological model was first developed for the identification of model parameters from cantilever creep tests, but it can be easily used to simulate drying stresses of a piece of wood subjected to no external load. It can therefore predict the stress reversal phenomenon, residual stresses and maximum stress through thickness during a typical drying process.

Buckling of thin-walled members by finite elements

Abstract We present a general two-dimensional thin plate/shell theory for the study of the elastic stability of sections formed by an assemblage of flat elements. These types of sections are generally analyzed by a one-dimensional model, but when, for instance, the width of the flanges is large or when there are openings in the section, the one-dimensional model cannot correctly predict the buckling load. We have developed a new finite element called DKM for the plate/shell model. We compare the result obtained with the present model with those of known analytical theories. The new model proves to be efficient and reliable. We also demonstrate that for wide plates, the analytical solution based on the one-dimensional model gives results slightly different from those of the proposed model.

Nonlinear analysis of composite bridges by the finite element method

Abstract The study of the nonlinear behaviour of composite bridges is quite complex. The difficulties can be attributed to the use of various materials and structural components and to their behaviour under different loading conditions. A sophisticated numerical tool is therefore required to improve our understanding of the structural behaviour of bridges. The finite element method is a powerful one which can be adopted to fulfill this task. In this paper, a plate/shell element (called DLTP), a shear connector element and a contact element for the nonlinear analysis of composite bridges are presented. The finite element procedure is based on small elasto-plastic strains and updated Lagrangian formulation to account for the large displacements and rotations of the structures. Various material models are developed to simulate the behaviour of steel, concrete and interface media (shear connectors, contact and friction) as well as phenomena encountered in the analysis of composite bridges. Numerical examples are presented for the validation of the proposed analytical procedure.

Transient response of isotropic, orthotropic and anisotropic composite-sandwich shells with the superparametric element

The first-order Reissner-Mindlin shear deformation theory (FOST) is employed to investigate the transient response of isotropic, layered orthotropic and anisotropic composite and sandwich shells. The eight-noded Serendipity and nine-noded Lagrangian quadrilateral superparametric shell elements are used. Numerical convergence and stability of the elements are established using an explicit central difference technique with a special mass matrix diagonalization scheme. The effects of transverse shear modulii of stiff layers, length/thickness and radius/length ratios, time step, finite element mesh, orientation of fibers and degree of orthotropy on the transient response of shells are studied. The variety of results presented here, based on realistic material properties of more commonly used advanced laminated composite shells, should serve as references for future investigations.

Challenges in Stub Hole Optimisation of Cast Iron Rodded Anodes

Reduction of cell voltage through redesign of the stub holes of cast iron rodded anodes is an attractive idea. In practice, stub hole optimisation is not an easy task and in situ trials may yield what seem to be counter-intuitive results.