CURRENT THEMES IN ENGINEERING SCIENCE 2008: Selected Presentations at the World Congress on Engineering—2008
1138(2009); http://dx.doi.org/10.1063/1.3155126View Description Hide Description
Numerical modelling can assist in understanding and predicting complex fracture processes. Smoothed Particle Hydrodynamics (SPH) is a particle‐based Lagrangian method that is particularly suited to the analysis of fracture due to its capacity to model large deformation and to track free surfaces generated. A damage model is used to predict the fracture of elastic solids. The damage parameter represents the volume‐averaged micro‐fracture of the volume of material represented by an SPH particle. Evolution of damage is predicted using the strain history of each particle. Damage inhibits the transmission of tensile stress between particles, and once it reaches unity, the interface becomes unable to transmit tensile stress, resulting in a macro‐crack. Connected macro‐cracks lead to complete fragmentation. In this paper, we explore the ability of an SPH‐based damage model to predict brittle fracture of rocks during impact. Rock shape is found to have considerable influence on the fracture process, the fragment sizes, the energy dissipation during impact, and the post‐fracture motion of the fragments.
Finite Element Analysis of Minimum Plastic Zone Radius criterion for crack initiation direction under mixed mode loading1138(2009); http://dx.doi.org/10.1063/1.3155125View Description Hide Description
The studies on crack‐tip plastic zones are of fundamental importance in describing the process of failure and in formulating various fracture criteria. The material fracture by opening mode (mode I) is not solely responsible for fracture propagation. Many industrial examples show the presence of mode II and mixed mode loading in machine/structural components. In the present study, the emphasis is placed on the analysis of the size and shape of the plastic zone at the crack tip under mixed mode loading conditions. The shape and size of crack‐tip plastic zones have been estimated by elastic finite element analysis in a Compact Tensile Shear (CTS) specimen under mixed mode loading according to von Mises yield criteria. The results obtained are used to analyze the minimum plastic zone radius (MPZR) criterion for crack‐initiation angle with reference to the loading angle and stress intensity factor.
1138(2009); http://dx.doi.org/10.1063/1.3155127View Description Hide Description
In science and engineering the concepts of size and scale play a key role in design. Many physical phenomena show a dependence on the size of objects and the scale of consideration. Of particular interest to the present study are the situations when the dependence of system response on the size appears to be complex, insofar as it is characterized by transitions in behaviour between different scales. Of particular importance is the connection between laboratory specimens and full scale objects and systems. In the context of modern technology, of increasing interest is the behaviour of nano‐scale objects as opposed to macroscopic. Scaling transitions and size effects in the fracture and strength of materials and structures have particular significance in modern science and engineering. The boundaries of scale of the mechanical phenomena studied and devices exploited are expanding, on the one hand, towards global scale phenomena, and on the other towards the nanometre scale processes. These circumstances challenge the conventional wisdom acquired over many decades, according to which laboratory experiments performed at the engineering scale (sub‐mm to a few meters) provide the source of material property data then used as input for modelling at the scale of the real object. When deviations from accepted scaling laws are found, new physical deformation mechanisms need to be proposed or identified, and new modelling approaches to be developed and validated. In this paper I review some examples of non‐trivial size dependence, and address a fundamental question of the efficient description of size effects and scale transitions. The functional description of multi‐scaling power law regimes is considered, and the functional form suitable for the task is identified. This form is then applied to a variety of experimental data manifesting size effects, including dual failure strength criteria (stress and toughness), fatigue crack growth thresholds and applications in the context of fretting fatigue, the Paris fatigue crack growth law, etc.
1138(2009); http://dx.doi.org/10.1063/1.3155128View Description Hide Description
The Finite Transfer Method is presented to solve a system of linear ordinary differential equations with boundary conditions. It is applied to determine the structural behaviour of the problem of a spatially curved beam element. The approach of this boundary value problem yields a unique system of differential equations. A Runge‐Kutta scheme is chosen to obtain Finite Transfer expressions. The use of a recurrence strategy in these equations permits one to relate both ends of the domain where boundary conditions are defined. An example of a Catenary‐shaped arch is provided for validation.
1138(2009); http://dx.doi.org/10.1063/1.3155129View Description Hide Description
The Euler‐Bernoulli uniform elastically supported beam model with various incorporated dissipation mechanisms is set into the framework of an abstract evolution differential equation. The damped linear visco‐elastic Kelvin solid model is presented as another possible application. Conditions are given to ensure oscillatory character of solutions.
1138(2009); http://dx.doi.org/10.1063/1.3155130View Description Hide Description
A new approach to the general formula of the magnetic field strength produced by a solenoid having the cross‐section of arbitrary shape is presented. The new approach is based on a theorem of vector analysis established by the author and presented below. The obtained expression is of a simpler form than the usual ones; however, the numerical computations have shown the accuracy of the results of the same order of magnitude as that of the application of the Biot‐Savart‐Laplace formula. Moreover, the derived formula contains, separately, the components of the magnetic field strength, namely, the Coulombian and non‐Coulombian ones, that is very interesting from a theoretical point of view. Consequently, in addition, the derived formula allows the direct introduction of the magnetic polarization and of the magnetic field state quantities.
1138(2009); http://dx.doi.org/10.1063/1.3155131View Description Hide Description
We present a synthetic division approach to compute partial fraction decompositions of rational functions. This method can determine the unknown partial fraction coefficients successively, without the need to use differentiation or to solve a system of linear equations. Examples of its applications in indefinite integration, Laurent series, inverse Laplace transform, linear ordinary differential equations, and linear recursive relations are provided.
1138(2009); http://dx.doi.org/10.1063/1.3155132View Description Hide Description
Mechanical properties of the fibers extracted from the areca are determined and compared with the other known natural fiber coir. Further these Areca fibers were chemically treated and the effect of this treatment on fiber strength is studied. Areca fiber composite laminates were prepared with randomly distributed fibers in Maize stalk fine fiber and Phenol Formaldehyde. Composite laminates were prepared with different proportions of phenol formaldehyde and fibers. Tensile test, moisture absorption test, and biodegradable tests on these laminates were carried out. Properties of these areca‐reinforced phenol formaldehyde composite laminates were analyzed and reported.
1138(2009); http://dx.doi.org/10.1063/1.3155133View Description Hide Description
This paper is devoted to the construction and evaluation of mass and stiffness matrices of elastodynamic four and five node infinite elements with unified shape functions (EIEUSF), recently proposed by the author. Such elements can be treated as a family of elastodynamic infinite elements appropriate for multi‐wave soil‐structure interaction problems. The common characteristic of the proposed infinite elements is the so‐called unified shape function, based on finite number of wave shape functions. The idea and the construction of the unified shape basis are described in brief. This element belongs to the decay class of infinite elements. It is shown that by appropriate mapping functions the formulation of such an element can be easily transformed to a mapped form. The results obtained using the proposed infinite elements are in a good agreement with the superposed results obtained by a series of standard computational models. The continuity along the finite/infinite element line (artificial boundary) in two‐dimensional substructure models is also discussed in brief. In this type of computational models such a line marks the artificial boundary between the near and the far field of the model.
1138(2009); http://dx.doi.org/10.1063/1.3155122View Description Hide Description
nanocomposite coatings with various amount of were prepared by electrodeposition technique. The effect of nanoparticulates in the Ni‐Fe nanocomposite coatings was investigated in relation to the ratio of to Na‐saccharine in the plating bath. X‐ray diffraction analysis showed that the Ni‐Fe nanocomposite coating has face‐centered cubic structure (FCC). However, a mixture of body‐centered cubic (BCC) and face‐centered cubic (FCC) phases was observed when the ratio of to Na‐saccharine was around 8.3. The crystallite size of the Ni‐Fe nanocomposite coating decreased when the ratio of to Na‐saccharine was increased. From the results of the elemental mapping procedure, it was found that inclusions of silicon were uniformly distributed in Ni‐Fe composite coating, indicating good dispersion of and this contributed in increasing the microhardness of coating.
1138(2009); http://dx.doi.org/10.1063/1.3155123View Description Hide Description
Monodisperse FePt nanoparticles were prepared by the co‐reduction of and precursors in water/triton X‐100/cyclohexane microemulsions. The as‐prepared samples with face‐centered cubic (fcc) structure were annealed at different temperatures and holding times in forming gas (95% Argon and 5% Hydrogen) atmosphere. X‐ray diffraction results showed that a minimum temperature of 650° C was required to initiate the formation of the ordered FePt face‐centered tetragonal (fct) ferromagnetic phase. The coercivity of the sample increased with increasing annealing temperature up to 750deg;thinsp;C. Annealing at temperatures above 750° C resulted in grain growth and a drop in coercivity. The lattice parameter of particles decreased when annealing time was increased. Annealing at 700° C for longer than 90 minutes caused phase transformation from fct to phase. FePt nanoparticles heated at 700° C for 90 minutes showed the highest coercivity of 3.04 kOe with specific area of
1138(2009); http://dx.doi.org/10.1063/1.3155124View Description Hide Description
Circular tubes have been widely used as structural members in many engineering applications. Therefore, their collapse behavior has been studied for many decades, focusing on the energy absorption characteristics and collapse mechanism. In general, there are various methods to predict the collapse behavior of tubes, such as the use of finite element codes or experiments. These tools provide results with high accuracy but are costly and require extensive running time. Therefore, an approximated model of tube attractive collapse mechanism is an alternative especially for the early step of design. For decades, many investigators have been working hard to construct a failure model of circular tube subjected to axial, bending, twisting or combined load. Although some of the results are promising, they still need more development. This paper also aims to develop a closed‐form solution to predict the response of a circular tube subjected to pure bending, focusing on the ovalisation regime. New ovalisation model was developed to include the effect of curvature into account. In order to validate the model, experiments were conducted with a number of tubes having various ratios. In addition, the available predictions from other investigators were also presented and compared. Good agreement was found between the theoretical predictions and experimental results. The present model provides more accurate results compared to some available theories.